Sensory system structure and functions. Processing, interaction and meaning of sensory information. Physiological mechanism of sound perception

As part of the sensory system, 3 departments are distinguished. 1) peripheral, consisting of receptors that perceive certain signals, and special formations that contribute to the work of receptors (this part is the sense organs eyes, ear, etc.); 2) conductor, including pathways and subcortical nerve centers; 3) cortical areas of the cerebral cortex to which this information is addressed.

The neural pathway connecting the receptor with cortical cells usually consists of four neurons: the first, sensory neuron is located outside the CNS in the spinal nodes or nodes of the cranial nerves (cochlear node, vestibular node, etc.); the second neuron is located in the spinal, medulla oblongata, or midbrain; the third neuron in the relay (switching) nuclei of the thalamus (interbrain); the fourth neuron is a cortical cell of the projection zone of the cerebral cortex.

The main functions of sensor systems:

• collection and processing of information about the external and internal environment of the body;
• the implementation of feedback that informs the nerve centers about the results of activities;
• maintaining a normal level (tonus) of the functional state of the brain.

I. P. Pavlov considered the decomposition of the complexities of the external and internal world into separate elements and their analysis as the main function of sensory systems (analyzers). In addition to the primary collection of information, an important function of sensory systems is also the implementation of feedback on the results of the body's activities. To clarify and improve various human actions, primarily motor ones, the central nervous system must receive information about the strength and duration of muscle contractions performed, about the speed and accuracy of body movements or working equipment, about changes in the rate of movements, about the degree of achievement of the goal, etc. Without this information, it is impossible to form and improve motor skills, including sports ones, and it is difficult to improve the technique of exercises performed.

Finally, sensory systems contribute to the regulation of the functional state of the organism. The impulse coming from various receptors to the cerebral cortex, both along specific and non-specific pathways, is an essential condition for maintaining a normal level of its functional state. Artificial switching off of the sense organs in special experiments on animals led to a sharp decrease in the tone of the cortex and falling asleep. Such an animal woke up only during feeding and with the urge to urinate or empty the intestines.

Classification and mechanisms of excitation of receptors

Receptors are called special formations that transform (convert) the energy of external irritation into the specific energy of a nerve impulse.

All receptors, according to the nature of the perceived environment, are divided into exoreceptors that receive stimuli from the external environment (receptors of the organs of hearing, vision, smell, taste, touch), interoreceptors that respond to stimuli from internal organs, and proprioceptors that perceive stimuli from the motor apparatus (muscles, tendons, articular capsules).

According to the type of perceived irritation, chemoreceptors are distinguished (receptors of the taste and olfactory sensory systems, chemoreceptors of blood vessels and internal organs); mechanoreceptors (proprioreceptors of the motor sensory system, baroreceptors of blood vessels, receptors of the auditory, vestibular, tactile and pain sensory systems); photoreceptors (receptors of the visual sensory system) and thermoreceptors (receptors of the temperature sensory system of the skin and internal organs).

By the nature of the connection with the stimulus, distant receptors are distinguished, which react to signals from distant sources and cause warning reactions of the body (visual and auditory) and contact, receiving direct influences (tactile, etc.).

According to structural features, primary and secondary receptors are distinguished. Primary receptors are the endings of sensitive bipolar cells whose body is outside the central nervous system, one process approaches the surface that perceives irritation, and the other goes to the central nervous system (for example, proprioreceptors, thermoreceptors, olfactory cells), Secondary receptors are represented by specialized receptor cells that are located between the sensitive neuron and the point of application of the stimulus (for example, the photoreceptors of the eye). In the primary receptors, the energy of the external stimulus is directly converted into a nerve impulse in the same cell. In the peripheral ending of sensitive cells, under the action of a stimulus, an increase in membrane permeability and its depolarization occurs, local excitation occurs - a receptor potential, which, having reached a threshold value, causes the appearance of an action potential propagating along the nerve fiber to the nerve centers.

In secondary receptors, the stimulus causes the appearance of a receptor potential in the receptor cell. Its excitation leads to the release of the mediator in the presynaptic part of the contact of the receptor cell with the fiber of the sensitive neuron. Local excitation of this fiber is reflected by the appearance of an excitatory postsynaptic potential or the so-called generator potential. When the threshold of excitability is reached in the fiber of the sensitive neuron, an action potential arises that carries information to the CNS. Thus, in secondary receptors, one cell converts the energy of an external stimulus into a receptor potential, and the other into a generator potential and an action potential.

Receptor Properties

The main property of receptors is their selective sensitivity to adequate stimuli. Most receptors are tuned to perceive one type (modality) of stimulus - light, sound, etc. The sensitivity of receptors to such stimuli specific to them is extremely high. The excitability of the receptor is measured by the minimum value of the energy of an adequate stimulus, which is necessary for the occurrence of excitation, i.e. arousal threshold.

Another property of receptors is the very low value of thresholds for adequate stimuli. For example, in the visual sensory system, excitation of photoreceptors can occur under the action of light energy, which is necessary to heat 1 ml of water per 1 gram. C for 60,000 years. Excitation of receptors can also occur under the action of inadequate stimuli (for example, the sensation of light in the visual system during mechanical and electrical stimulation). However, in this case, the excitation thresholds are much higher.

There are absolute and difference (differential) thresholds.

Absolute thresholds are measured by the minimum perceived magnitude of the stimulus. Differential thresholds represent the minimum difference between two stimulus intensities that is still perceived by the body (differences in color shades, light brightness, degree of muscle tension, articular angles, etc.).

The fundamental property of all living things is adaptation, that is, adaptability to environmental conditions. Adaptation processes cover not only receptors, but also all parts of sensory systems. Adaptation of peripheral elements is manifested in the fact that the excitation thresholds of receptors are not a constant value. By raising the thresholds of excitation, that is, by reducing the sensitivity of the receptors, adaptation to prolonged monotonous stimuli occurs. For example, a person does not feel constant pressure on the skin of his clothes, does not notice the continuous ticking of the clock.

But the speed of adaptation to prolonged stimuli receptors are divided into rapidly adapting (phasic) and slowly adapting (tonic). Phase receptors react only at the beginning or at the end of the action of the stimulus with one or two impulses (for example, skin receptors Pacinian pressure-bodies), atonic ones continue to send unrelenting information to the CNS for a long time of the stimulus (for example, the so-called secondary endings in the muscle spindles, which inform the CNS about static stresses).

Adaptation can be accompanied by both a decrease and an increase in the excitability of receptors. So, when moving from a bright room to a dark one, there is a gradual increase in the excitability of the photoreceptors of the eye, and a person begins to distinguish dimly lit objects - this is the so-called dark adaptation. However, such a high excitability of the receptors turns out to be excessive when moving into a brightly lit room (“the light hurts the eyes”). Under these conditions, the excitability of photoreceptors rapidly decreases - light adaptation occurs.

The nervous system finely regulates the sensitivity of receptors depending on the needs of the moment through efferent regulation of receptors. In particular, during the transition from a state of rest to muscular work, the sensitivity of the receptors of the motor apparatus increases markedly, which facilitates the perception of information about the state of the musculoskeletal system (gamma regulation). The mechanisms of adaptation to different stimulus intensities can affect not only the receptors themselves, but also other formations in the sense organs. For example, when adapting to different sound intensities, there is a change in the mobility of the auditory ossicles (hammer, anvil and stirrup) in the human middle ear.

Information encoding

The amplitude and duration of individual nerve impulses (action potentials) coming from the receptors to the centers remain constant under different stimuli. However, the receptors transmit adequate information to the nerve centers not only about the nature, but also about the strength of the acting stimulus. Information about changes in the intensity of the stimulus is encoded (transformed into the form of a nerve impulse code) in two ways:

1) a change in the frequency of impulses going along each of the nerve fibers from receptors to nerve centers, and 2) a change in the number and distribution of impulses - their number in a pack, intervals between packs, the duration of individual bursts of impulses, the number of simultaneously excited receptors and corresponding nerve fibers ( a diverse spatio-temporal picture of this impulsation, rich in information, is called a pattern).

The greater the intensity of the stimulus, the greater the frequency of afferent nerve impulses and their number. This is due to the fact that the growth stimulus strength leads to an increase in the depolarization of the receptor membrane, which, in turn, causes an increase in the amplitude of the generator potential and an increase in the frequency of impulses arising in the nerve fiber. Between the logarithm of the strength of irritation and the number of nerve impulses there is a directly proportional relationship.

There is another possibility of encoding sensory information. The selective sensitivity of receptors to adequate stimuli already makes it possible to separate different types of energy acting on the body. However, even within the same sensory system, there may be different sensitivity of individual receptors to stimuli of the same modality with different characteristics (distinguishing taste characteristics by different taste buds of the tongue, color discrimination by different photoreceptors of the eye, etc.).

visual sensory system

The visual sensory system serves to perceive and analyze light stimuli. Through it, a person receives up to 80-90% of all information about the external environment. The human eye perceives light rays only in the visible part of the spectrum in the range from 400 to 800 nm.

General organization plan

The visual sensory system consists of the following departments:

1. the peripheral section is a complex auxiliary organ - the eyes, in which there are photoreceptors and bodies of 1 (bipolar) and 2 (ganglion) neurons;
2. the conductive department is the optic nerve (the second pair of cranial nerves), which is the fibers of the 2nd neurons and partially intersects in the chiasm, transmits information to the third neurons, some of which are located in the anterior colliculus of the midbrain, the other part in the nuclei of the diencephalon, so called external cranked bodies;
3. cortical section 4th neurons are located in the 17th field of the occipital region of the cerebral cortex. This formation is the primary (projection) field or core of the analyzer, the function of which is the emergence of sensations. Next to it is a secondary field or periphery of the analyzer (fields 18 and 19), whose function is to recognize and comprehend visual sensations, which underlies the process of perception. Further processing and interconnection of visual information with information from other sensory systems occurs in the associative posterior tertiary cortical fields - the lower parietal areas.

Light-conducting media of the eye and refraction of light (refraction)

The eyeball is a spherical chamber with a diameter of about 2.5 cm, containing light-conducting media - the cornea, the moisture of the anterior chamber, the lens and the gelatinous fluid - the vitreous body, the purpose of which is to refract light rays and focus them in the area of ​​the receptors on the retina. The walls of the chamber are 3 shells. The outer opaque shell sclera passes in front of the transparent cornea. The middle choroid in the anterior part of the eye forms the ciliary body and the iris, which determines the color of the eyes. In the middle of the iris (iris) there is a hole the pupil that regulates the amount of light rays transmitted. Pupil diameter is regulated by the pupillary reflex, the center of which is located in the midbrain. The inner retina (retina) or retina contains the photoreceptors of the eye rods and cones and serves to convert light energy into nervous excitation. The refractive media of the eye, by refracting light rays, provide a clear image on the retina. The main refractive media of the human eye are the cornea and the lens. Rays coming from infinity through the center of the cornea and lens (i.e. through the main optical axis of the eye) perpendicular to their surface do not experience refraction. All other rays are refracted and converge inside the chamber of the eye at one point focus. The adaptation of the eye to a clear vision of objects at different distances (its focusing) is called accommodation. This process in humans is carried out by changing the curvature of the lens. The near point of clear vision shifts with age (from 7 cm at 7-10 years old to 75 cm at 60 years old or more), as the elasticity of the lens decreases and accommodation worsens. There is senile farsightedness.

Normally, the length of the eye corresponds to the refractive power of the eye. However, 35% of people have violations of this correspondence. In the case of myopia, the length of the eye is greater than normal and the focusing of the rays occurs in front of the retina, and the image on the retina becomes blurry. In a far-sighted eye, on the contrary, the length to the eye is less than normal and the focus is located behind the retina. As a result, the image on the retina is also blurry.

photoreception

The photoreceptors of the eye (rods and cones) are highly specialized cells that convert light stimuli into nervous excitation. Photoreception begins in the outer segments of these cells, where visual pigment molecules are located on special disks, like on shelves (in rods - rhodopsin, in cones - varieties of its analogue). Under the action of light, a series of very rapid transformations and discoloration of the visual pigment occurs. In response to a stimulus, these receptors, unlike all other receptors, form a receptor potential in the form of inhibitory changes on the cell membrane. In other words, hyperpolarization of the membranes of receptor cells occurs in the light, and in the dark, their depolarization, i.e., the stimulus for them is darkness, not light. At the same time, reverse changes occur in neighboring cells, which makes it possible to separate light and dark points of space. Photochemical reactions in the outer segments of the photoreceptors cause changes in the membranes of the rest of the receptor cell, which are transmitted to bipolar cells (first neurons), and then to ganglion cells (second neurons), from which nerve impulses are sent to the brain. Some ganglion cells are excited in the light, some in the dark.

Rods, scattered mainly along the periphery of the retina (there are 130 million of them), and cones, located mainly in the central part of the retina (there are 7 million of them), differ in their functions (Fig. 1-A). The rods are more sensitive than the cones and are organs of twilight vision. They perceive a black and white (colorless) image. Cones are organs of daytime vision. They provide color vision. There are 3 types of cones in humans: predominantly red, green, and blue-violet. Their different color sensitivity is determined by differences in visual pigment. Combinations of excitation of these receivers of different colors give sensations of the whole gamut of color shades, and uniform excitation of all three types of cones sensation of white color. When cone function is impaired, color blindness (color blindness) occurs, a person ceases to distinguish colors, in particular, red and green color. This disease occurs in 8% of men and 0.5% of women.

Functional characteristics of vision

Visual acuity and field of vision are important characteristics of the organ of vision.

Visual acuity is the ability to distinguish individual objects. It is measured by the minimum angle at which two points are perceived as separate, approximately 0.5 arcminutes. In the center of the retina, the cones are smaller and much denser, so the ability for spatial discrimination is 4-5 times higher here than at the periphery of the retina. Therefore, central vision has a higher visual acuity than peripheral vision. For a detailed examination of objects, a person by turning his head and eyes moves their image to the center of the retina.

Rice. 1. Receptors of sensory systems
A: photoreceptors. Cones (1) and rods (2).
B: auditory receptors. 1 vestibular ladder, 2 tympanic
staircase, 3 membranous canal of the cochlea, 4 vestibular membrane.
5 main membrane, 6-integumentary membrane, 7 hair cells,
8 afferent nerve fibers, 9 spiral nerve cells
ganglion (first neurons). C and D: vestibular receptors.
B otolith apparatus. 1 otolithic membrane, 2 otoliths (crystals of calcium carbonate), 3 hair receptor cells,
4 fibers of the vestibular nerve. G semicircular canals. 1 fiber of the vestibular nerve, 2 ampulla,
3 cupula with hair receptor cells,
4 semicircular canal. The arrows show the direction of cupula oscillations during inertial displacements of the endolymph.
D: proprioceptors. Muscle spindle. 1 afferent nervous
fiber, 2 extrafusal muscle fibers (cut),
3 intrafusiform (intrafusal) muscle fibers,
4 spindle sheath, 5 core, 6 nuclear bag,
7- sensitive nerve endings,
8 efferent nerve gamma fibers, 9 tendon.
Tendon organ. 1 afferent nerve fiber,
2 muscle fibers, 3- tendon, 4- capsule,
5 sensitive nerve endings.

Visual acuity depends not only on the density of the receptors, but also on the clarity of the image on the retina, that is, on the refractive properties of the eye, on the degree of accommodation, and on the size of the pupil. In the aquatic environment, the refractive power of the cornea decreases, since its refractive index is close to that of water. As a result, visual acuity decreases by 200 times under water.

The field of view is the part of space visible when the eye is stationary. For black and white signals, the field of view is usually limited by the structure of the bones of the skull and the position in the eye sockets of the eyeballs. For colored stimuli, the field of view is smaller, since the cones that perceive them are located in the central part of the retina. The smallest field of view is noted for green. With fatigue, the field of view decreases.

A person has binocular vision, i.e. vision with two eyes. Such vision has an advantage over monoocular vision (one eye) in the perception of the depth of space, especially at close distances (less than 100 m). The clarity of such perception (eye) is ensured by good coordination of the movement of both eyes, which must be accurately aimed at the object in question. In this case, its image falls on identical points of the retina (equally distant from the center of the retina) and the person sees one image. A clear rotation of the eyeballs depends on the work of the external muscles of the eye of its oculomotor apparatus (four straight and two oblique muscles), in other words, on the muscular balance of the eye. However, only 40% of people have ideal eye muscle balance or orthophoria. Its violation is possible as a result of fatigue, the action of alcohol, etc., as well as as a result of muscle imbalance, which leads to blurred and bifurcated images (heterophoria). With small imbalances in the balance of muscle efforts, a slight latent (or physiological) strabismus is observed, which in an alert state a person compensates with volitional regulation, and with significant obvious strabismus.

The oculomotor apparatus is important in the perception of the speed of movement, which a person evaluates either by the speed of movement of an image along the retina of a stationary eye, or by the speed of movement of the external muscles of the eye during servo eye movements.

The image that a person sees with two eyes is primarily determined by his leading eye. The dominant eye has a higher visual acuity, instantaneous and especially bright color perception, a wider field of view, a better sense of depth of space. When aiming, only what is included in the field of view of this eye is perceived. In general, the perception of the object is largely provided by the leading eye, and the perception of the surrounding background is provided by the non-leading eye.

auditory sensory system

The auditory sensory system serves to perceive and analyze the sound vibrations of the external environment. It acquires a particularly important meaning for a person and its connection with the development of verbal communication between people. The activity of the auditory sensory system is also important for assessing time intervals - the pace and rhythm of movements.

General organization plan

The auditory sensory system consists of the following sections:

1. the peripheral section, which is a complex specialized organ consisting of the outer, middle and inner ear;
2. conductive department the first neuron of the conductive department, located in the spiral node of the cochlea, receives excitation from the receptors of the inner ear, from here information flows along its fibers, i.e. along the auditory nerve (part of 8 pairs of cranial nerves) to the second neuron in the medulla oblongata brain and after decussation, part of the fibers goes to the third neuron in the posterior colliculus of the midbrain, and part to the nuclei of the diencephalon - the internal geniculate body;
3. the cortical section is represented by the fourth neuron, which is located in the primary (projection) auditory field and temporal region of the cerebral cortex and provides the appearance of sensation, and more complex processing sound information occurs in a nearby secondary auditory field, which is responsible for the formation of perception and recognition of information. The received information enters the tertiary field of the lower parietal zone, where it is integrated with other forms of information.

Functions of the outer, middle and inner ear

The outer ear is a sound pickup apparatus.

Sound vibrations are picked up by the auricles (in animals they can turn towards the sound source) and transmitted through the external auditory canal to the tympanic membrane, which separates the outer ear from the middle ear. Picking up sound and the whole process of hearing with two ears so-called binaural hearing is important for determining the direction of the sound. Sound vibrations coming from the side reach the nearest ear a few ten-thousandths of a second (0.0006 s) earlier than the other. This negligible difference in the time the sound arrives at both ears is enough to determine its direction.

The middle ear is a sound-conducting apparatus. It is an air cavity, which through the auditory (Eustachian) tube is connected to the nasopharyngeal cavity. Vibrations from the tympanic membrane through the middle ear are transmitted by 3 auditory ossicles connected to each other hammer, anvil and stirrup, and the latter through the membrane of the oval window transmits these vibrations of the fluid in the inner ear, perilymph. Thanks to the auditory ossicles, the amplitude of the oscillations decreases, and their strength increases, which makes it possible to set in motion a column of fluid in the inner ear. With strong sounds, special muscles reduce the mobility of the eardrum and auditory ossicles, adapting the hearing aid to such changes in the stimulus and protecting the inner ear from destruction. Due to the connection through the auditory tube of the air cavity of the middle ear with the cavity of the nasopharynx, it becomes possible to equalize the pressure on both sides of the tympanic membrane, which prevents its rupture during significant changes in pressure in the external environment when diving under water, climbing to a height, shooting, etc. This is the barofunction of the ear .

The inner ear is a sound-receiving apparatus. It is located in the pyramid of the temporal bone and contains the cochlea, which in humans forms 2.5 spiral coils. The cochlear canal is divided by two partitions by the main membrane and the vestibular membrane into 3 narrow passages: the upper one (scala vestibularis), the middle one (the membranous canal) and the lower one (the scala tympani). At the top of the cochlea there is a hole connecting the upper and lower channels into a single one, going from the oval window to the top of the cochlea and further to the round window. Its cavity is filled with a liquid - perilymph, and the cavity of the middle membranous canal is filled with a liquid of a different composition - endolymph. In the middle canal there is a sound-receiving apparatus - the organ of Corti, in which there are mechanoreceptors of sound vibrations - hair cells.

Physiological mechanism of sound perception

The perception of sound is based on two processes occurring in the cochlea: 1) the separation of sounds of different frequencies at the place of their greatest impact on the main membrane of the cochlea and 2) the transformation of mechanical vibrations into nervous excitation by receptor cells. Sound vibrations entering the inner ear through the oval window are transmitted to the perilymph, and the vibrations of this fluid lead to displacements of the main membrane. The height of the column of the oscillating liquid and, accordingly, the place of the greatest displacement of the main membrane depends on the height of the sound: high-frequency sounds have the greatest effect at the beginning of the main membrane, and low frequencies reach the top of the cochlea. Thus, with sounds of different frequencies, different hair cells and different nerve fibers are excited, i.e., a spatial code is implemented. An increase in sound intensity leads to an increase in the number of excited hair cells and nerve fibers, which makes it possible to distinguish the intensity of sound vibrations.

The hairs of receptor cells are immersed in the integumentary membrane. When the main membrane vibrates, the hair cells located on it begin to shift and their hairs are mechanically irritated by the integumentary membrane. As a result, an excitation process occurs in the hair receptors, which is directed along the afferent fibers to the neurons of the cochlear spiral ganglion and further to the CNS (Fig. 1-B).

Distinguish between bone and air conduction of sound. Under normal conditions, air conduction predominates in humans - the conduction of sound vibrations through the outer and middle ear to the receptors of the inner ear. In the case of bone conduction, sound vibrations are transmitted through the bones of the skull directly to the cochlea (for example, when diving, scuba diving).

A person usually perceives sounds with a frequency of 15 to 20,000 Hz (in the range of 10-11 octaves). In children, the upper limit reaches 22,000 Hz, with age it decreases. The highest sensitivity was found in the frequency range from 1000 to 3000 Hz. This area corresponds to the most frequently occurring frequencies in human speech and music.

vestibular sensory system

The vestibular sensory system serves to analyze the position and movement of the body in space. This is one of the oldest sensory systems, developed under the influence of gravity on earth. The impulses of the vestibular apparatus are used in the body to maintain the balance of the body, to regulate and maintain posture, for the spatial organization of human movements.

General organization plan

The vestibular sensory system consists of the following departments:

1. the peripheral section includes two formations containing mechanoreceptors of the vestibular system - the vestibule (pouch and uterus) and semicircular canals;
2. the conductive section starts from the receptors with fibers of the bipolar cell (the first neuron) of the vestibular ganglion located in the temporal bone, other processes of these neurons form the vestibular nerve and, together with the auditory nerve, as part of the 8th pair of cranial nerves, enter the medulla oblongata; in the vestibular nuclei of the medulla oblongata are the second neurons, the impulses from which go to the third neurons in the thalamus (interbrain);
3. the cortical region is represented by the fourth neurons, some of which are represented in the projection (primary) field of the vestibular system in the temporal region of the cortex, and the other part is located in close proximity to the pyramidal neurons of the motor cortex and in the postcentral gyrus. The exact localization of the cortical part of the vestibular sensory system in humans has not yet been established.

The functioning of the vestibular apparatus

The peripheral part of the vestibular sensory system is located in the inner ear. Channels and cavities in the temporal bone form a bony labyrinth of the vestibular apparatus, which is partially filled with a membranous labyrinth. Between the bony and membranous labyrinths there is a fluid - perilymph, and inside the membranous labyrinth - endolymph.

The vestibule apparatus is designed to analyze the effect of gravity upon changes in the position of the body in space and accelerations of rectilinear motion. The membranous labyrinth of the vestibule is divided into 2 cavities - the sac and the uterus, containing otolith devices. The mechanoreceptors of otolithic devices are hair cells. They are glued together with a gelatinous mass that forms an otolithic membrane over the hairs, in which there are crystals of calcium carbonate - otoliths (Fig. 1-B). In the uterus, the otolithic membrane is located in the horizontal plane, and in the sac it is bent and is located in the frontal and sagittal planes. With a change in the position of the head and body, as well as with vertical or horizontal accelerations, the otolithic membranes move freely under the action of gravity in all three planes, pulling, compressing, or bending the mechanoreceptor hairs. The greater the deformation of the hairs, the higher the frequency of afferent impulses in the fibers of the vestibular nerve.

The apparatus of the semicircular canals is used to analyze the effect of centrifugal force during rotational movements. Its adequate irritant is angular acceleration. Three arcs of the semicircular canals are located in three mutually perpendicular planes: anterior in the frontal plane, lateral in the horizontal, posterior in the sagittal plane. At one end of each channel there is an extension ampoule. The hairs of sensitive cells located in it are glued together into a scallop - an ampullar cupula. It is a pendulum that can deviate as a result of the difference in endolymph pressure on opposite surfaces of the cupula (Fig. 1-D). During rotational movements, as a result of inertia, the endolymph lags behind the movement of the bone part and exerts pressure on one of the surfaces of the cupula. Deviation of the cupula bends the hairs of the receptor cells and causes the appearance of nerve impulses in the vestibular nerve. The greatest changes in the position of the cupula occur in that semicircular canal, the position of which corresponds to the plane of rotation.

At present, it has been shown that rotations or tilts in one direction increase afferent impulses, and in the other direction, they decrease it. This makes it possible to distinguish between the direction of rectilinear or rotary motion.

Influence of irritations of the vestibular system on other functions of the body

The vestibular sensory system is associated with many centers of the spinal cord and brain and causes a number of vestibulo-somatic and vestibulo-vegetative reflexes.

Vestibular irritations cause adjusting reflexes of changes in muscle tone, lifting reflexes, as well as special eye movements aimed at preserving the image on the retina. nystagmus (movement of the eyeballs with a speed of rotation, but in the opposite direction, then a quick return to the starting position and a new opposite rotation).

In addition to the main analyzer function, which is important for controlling the posture and movements of a person, the vestibular sensory system has a variety of side effects on many body functions that arise as a result of irradiation of excitation to other nerve centers with low stability of the vestibular apparatus. Its irritation leads to a decrease in the excitability of the visual and skin sensory systems, a deterioration in the accuracy of movements. Vestibular irritations lead to impaired coordination of movements and gait, changes in heart rate and blood pressure, an increase in the time of a motor reaction and a decrease in the frequency of movements, a deterioration in the sense of time, a change mental functions attention, operational thinking, short-term memory, emotional manifestations, In severe cases, there are dizziness, nausea, vomiting. An increase in the stability of the vestibular system is achieved to a greater extent by active rotations of a person than by passive ones.

Under conditions of weightlessness (when a person's vestibular influences are turned off), there is a loss of understanding of the direction of the gravitational vertical and the spatial position of the body. Loss of walking and running skills. Condition worsens nervous system, there is increased irritability, mood instability.

motor sensory system

The motor sensory system is used to analyze the state of the motor apparatus its movement and position. Information about the degree of contraction of skeletal muscles, tension of tendons, changes in articular angles is necessary for the regulation of motor acts and postures.

General organization plan

The motor sensory system consists of the following 3 departments:

1. peripheral section, represented by proprioceptors located in muscles, tendons and articular bags;
2. conductor and department, which begins with bipolar cells (the first neurons), whose bodies are located outside the central nervous system in the spinal nodes. One of their processes is associated with receptors, the other enters the spinal cord and transmits proprioceptive impulses to the second neurons in the medulla oblongata (part of the pathways from the proprioreceptors go to the cerebellar cortex), and then to the third neurons - the relay nuclei of the thalamus (to the diencephalon);
3. the cortical section is located in the anterior central gyrus of the cerebral cortex.

Functions of proprioreceptors

Proprioreceptors include muscle spindles, tendon organs (or Golgi organs), and articular receptors (receptors for the articular capsule and articular ligaments). All these receptors are mechanoreceptors, the specific stimulus of which is their stretching.

Muscle spindles are attached to muscle fibers in parallel - one end to the tendon, and the other to the fiber. Each spindle is covered with a capsule formed by several layers of cells, which expands in the central part and forms a nuclear bag. The spindle contains several (from 2 to 14) thin intrafusiform or so-called intrafusal muscle fibers. These fibers are 2-3 times thinner than normal skeletal muscle fibers (extrafusal).

Intrafusal fibers are divided into two types: 1) long, thick, with nuclei in the nuclear bag, which are associated with the thickest and fastest conducting afferent nerve fibers they inform about the dynamic component of movement (the rate of change in muscle length) and 2) short, thin, with nuclei extended into a chain, informing about the static component (the length of the muscle being held at the moment). The endings of the afferent nerve fibers are wound around the intrafusal fibers of the receptor. When the skeletal muscle is stretched, the muscle receptors are also stretched, which deforms the endings of the nerve fibers and causes the appearance of nerve impulses in them. The frequency of proprioceptive impulses increases with an increase in muscle stretch, as well as with an increase in the speed of its stretch. Thus, the nerve centers are informed about the speed of muscle stretching and its length. Due to low adaptation, impulses from muscle spindles continue throughout the entire period of maintaining the stretched state, which ensures that the centers are constantly aware of the length of the muscle. The more subtle and coordinated movements the muscles carry out, the more muscle spindles they have: in a person, in the deep muscles of the neck that connect the spine with the head, their average number is 63, and in the muscles of the thigh and pelvis there are less than 5 spindles per 1 g of muscle mass ( Fig. 1-D).

The CNS can finely regulate the sensitivity of proprioreceptors. Discharges of small gamma motor neurons of the spinal cord cause contraction of intrafusal muscle fibers on both sides of the nuclear spindle bag. As a result, the middle irreducible part of the muscle spindle is stretched, and the deformation of the outgoing nerve fiber causes an increase in its excitability. Moreover, with the same length of the skeletal muscle, a greater number of afferent impulses will enter the nerve centers. This allows, firstly, to single out proprioceptive impulses against the background of other afferent information and, secondly, to increase the accuracy of the analysis of the state of the muscles. An increase in the sensitivity of the spindles occurs during movement and even in the prelaunch state. This is explained by the fact that, due to the low excitability of gamma motor neurons, their activity at rest is weakly expressed, and during voluntary movements and vestibular reactions, it is activated. The sensitivity of proprioreceptors also increases with moderate stimulation of sympathetic fibers and the release of small doses of adrenaline.

The tendon organs are located at the point of transition of muscle fibers into tendons. Tendon receptors (the endings of nerve fibers) braid thin tendon fibers surrounded by a capsule. As a result of the successive attachment of the tendon organs to the muscle fibers (and in some cases to the muscle spindles), the tendon mechanoreceptors are stretched when the muscles are tense. Thus, unlike muscle spindles, tendon receptors inform the nerve centers about the degree of tension in the mouse, and the rate of its development.

Articular receptors inform about the position of individual parts of the body in space and relative to each other. These receptors are free nerve endings or endings enclosed in a special capsule. Some articular receptors send information about the magnitude of the articular angle, i.e., about the position of the joint. Their impulsation continues throughout the entire period of conservation of this angle. It is the greater the frequency, the greater the angle shift. Other articular receptors are excited only at the moment of movement in the joint, that is, they send information about the speed of movement. The frequency of their impulses increases with an increase in the rate of change in the articular angle.

The signals coming from the receptors of muscle spindles, tendon organs, articular bags and tactile skin receptors are called kinesthetic, that is, informing about the movement of the body. Their participation in voluntary regulation of movements is different. Signals from articular receptors cause a noticeable reaction in the cerebral cortex and are well understood. Thanks to them, a person perceives differences in joint movements better than differences in the degree of muscle tension in static positions or weight maintenance. Signals from other proprioceptors, coming mainly to the cerebellum, provide unconscious regulation, subconscious control of movements and postures.

Sensory systems of the skin, internal organs, taste and smell

in skin and internal organs There are a variety of receptors that respond to physical and chemical stimuli.

Skin reception

Tactile, temperature and pain reception is represented in the skin. On 1 cm2 of skin, on average, there are 12-13 cold points, 1-2 thermal points, 25 tactile points and about 100 pain points.

The tactile sensor system is designed for pressure and touch analysis. Its receptors are free nerve endings and complex formations (Meissner bodies, Pacchini bodies), in which the nerve endings are enclosed in a special capsule. They are located in the upper and lower layers of the skin, in the skin vessels, at the base of the hair. Especially there are a lot of them on the fingers and toes, palms, soles, lips. These are mechanoreceptors that respond to stretching, pressure and vibration. The most sensitive receptor is the Paccini body. which causes a sensation of touch when the capsule is displaced by only 0.0001 mm. The larger the body of Paccini, the thicker and faster the afferent nerves depart from it. They conduct short bursts (duration 0.005 s), informing about the beginning and end of the action of a mechanical stimulus. The path of tactile information is as follows: receptor - 1st neuron in the spinal nodes - 2nd neuron in the spinal cord or medulla oblongata 3rd neuron in the diencephalon (thalamus) 4th neuron in the posterior central gyrus of the cerebral cortex (primary somatosensory zone).

Temperature reception is carried out by cold receptors (Krause flasks) and thermal (Ruffini bodies, Golgi-Mazzoni). At a skin temperature of 31-37°C, these receptors are almost inactive. Below this limit, cold receptors are activated in proportion to the temperature drop, then their activity drops and completely stops at +12°C. At temperatures above 37°C, thermal receptors are activated, reaching their maximum activity at +43°C, then abruptly stop responding.

Pain reception, according to most experts, does not have special perceiving formations. Painful stimuli are perceived by free nerve endings, and also occur with strong thermal and mechanical stimuli in the corresponding thermo- and mechanoreceptors.

Temperature and pain stimuli are transmitted to the spinal cord, from there to the diencephalon and to the somatosensory area of ​​the cortex.

Visceroceptive (interoreceptive) sensory system

In the internal organs there are many receptors that perceive pressure - vascular baroreceptors, intestinal tract and others, changes in the chemistry of the internal environment - chemoreceptors, its temperature - thermoreceptors, osmotic pressure, pain stimuli. With their help, the constancy of various constants of the internal environment (maintenance of homeostasis) is regulated by an unconditional reflex way, the central nervous system is informed about changes in the internal organs. Information from interoreceptors through the vagus, celiac and pelvic nerves enters the diencephalon and then to the frontal and other areas of the cerebral cortex. The activity of this system is practically not realized, it is poorly localized, however, with strong irritations, it is well felt. It is involved in the formation of complex sensations thirst, hunger, etc.

Olfactory and gustatory sensory systems

The olfactory and gustatory sensory systems are among the most ancient systems. They are designed to perceive and analyze chemical stimuli coming from the external environment. Olfactory chemoreceptors are located in the olfactory epithelium of the upper nasal passages. These are hairy bipolar cells that transmit information through the ethmoid bone of the skull to the cells of the olfactory bulb of the brain and further through the olfactory tract to the olfactory cortical zones (the hook of the sea horse, the gyrus of the hippocampus, and others). Different receptors respond selectively to different molecules of odorous substances, being excited only by those molecules that are a mirror copy of the surface of the receptor. They perceive ethereal, camphor, mint, musky, and other odors, and their sensitivity to certain substances is unusually high.

Taste chemoreceptors are taste buds located in the epithelium of the tongue, posterior pharynx, and soft palate. In children, their number is greater, and with age decreases. Microvilli of receptor cells protrude from the bulb to the surface of the tongue and react to substances dissolved in water. Their signals come through the fibers of the facial and glossopharyngeal nerves (medulla oblongata) to the thalamus and further to the somatosensory cortex. Receptors in different parts of the tongue perceive four basic tastes: bitter (back of the tongue), sour (edges of the tongue), sweet (front of the tongue), and salty (front and edges of the tongue). Between taste and chemical structure substances there is no strict correspondence, since taste sensations can change with illness, pregnancy, conditioned reflex effects, changes in appetite. Smell, tactile, pain and temperature sensitivity are involved in the formation of taste sensations. The information of the gustatory sensory system is used to organize eating behavior associated with the acquisition, choice, preference or rejection of food, the formation of a feeling of hunger, satiety.

Processing, interaction and meaning of sensory information

Sensory information is transmitted from receptors to the higher parts of the brain along two main pathways of the nervous system - specific and non-specific. Specific pathways make up one of the three main functional blocks of the brain - a block for receiving, processing and storing information. These are the classic afferent pathways of the visual, auditory, motor, and other sensory systems. A nonspecific brain system also participates in the processing of this information, which does not have direct connections with peripheral receptors, but receives impulses via collaterals from all ascending specific systems and ensures their extensive interaction.

Processing of sensory information in conductor departments

The analysis of the received irritations occurs in all departments of the sensory systems. The simplest form of analysis is carried out as a result of the selection by specialized receptors of stimuli of various modalities (light, sound, etc.) from all the impacts falling on the body. In this case, in one sensory system, a more detailed selection of signal characteristics is already possible (color discrimination by cone photoreceptors, etc.).

An important feature in the work of the conductor department of sensory systems is the further processing of afferent information, which consists, on the one hand, in the ongoing analysis of the properties of the stimulus, and on the other hand, in the processes of their synthesis, in the generalization of the information received. As afferent impulses are transmitted to higher levels of sensory systems, the number of nerve cells, which respond to afferent signals more complex than simple conductors. For example, at the level of the midbrain in the subcortical visual centers there are neurons that respond to varying degrees of illumination and detect movement, in the subcortical auditory centers there are neurons that extract information about the pitch and localization of sound, the activity of these neurons underlies the orienting reflex to unexpected stimuli .

Due to the many branchings of afferent pathways at the level of the spinal cord and subcortical centers, multiple interactions of afferent impulses within one sensory system, as well as interactions between different sensory systems, are ensured (in particular, extremely extensive interactions of the vestibular sensory system with many ascending and descending pathways can be noted). Particularly wide opportunities for the interaction of various signals are created in the non-specific system of the brain, where impulses of various origins (from 30,000 neurons) and from different receptors of the body can converge (converge) to the same neuron. As a result, the nonspecific system plays an important role in the processes of integration of functions in the body.

Upon entering the higher levels of the nervous system, the sphere of signaling coming from one receptor expands. For example, in the visual system, the signals of one receptor are connected (through a system of additional retinal nerve cells - horizontal, etc.) with dozens of ganglion cells and can, in principle, transmit information to any cortical neurons of the visual cortex. On the other hand, as signals are passed, information is compressed. For example, one retinal ganglion cell combines information from hundreds of bipolar cells and tens of thousands of receptors, i.e., such information enters the optic nerves after significant processing, in an abbreviated form.

An essential feature of the activity of the conductor department of sensory systems is the transmission without distortion of specific information from receptors to the cerebral cortex. A large number of parallel channels (900,000 fibers in the optic nerve, 30,000 fibers in the auditory nerve) helps to preserve the specifics of the transmitted message, and the processes of lateral (lateral) inhibition isolate these messages from neighboring cells and pathways.

One of the most important aspects of processing afferent information is the selection of the most significant signals, carried out by ascending and descending influences at various levels of sensory systems. This selection also involves a non-specific part of the nervous system (limbic system, reticular formation). By activating or inhibiting many central neurons, it contributes to the selection of the most significant information for the body. In contrast to the extensive influences of the midbrain part of the reticular formation, impulses from the nonspecific nuclei of the thalamus affect only limited areas of the cerebral cortex. Such a selective increase in the activity of a small area of ​​the cortex is important in organizing the act of attention, highlighting the most important messages at the moment against the general afferent background.

Information processing at the cortical level

In the cerebral cortex, the complexity of information processing increases from primary fields to its secondary and tertiary fields. So, simple cells of the primary fields of the visual cortex are detectors of black and white boundaries of straight lines perceived by small areas of the retina, while complex and supercomplex neurons of the secondary visual fields detect the length of lines, their angles of inclination, various contours of figures, the direction of movement of objects, there are cells that identify familiar faces of people, etc.

The primary fields of the cortex carry out the analysis of stimuli of a certain modality coming from specific receptors associated with them. These are the so-called nuclear zones of analyzers. according to I. P. Pavlov (visual, auditory, etc.). Their activity underlies the emergence of sensations. The secondary fields lying around them (the periphery of the analyzers) receive the results of information processing from the primary fields and transform them into more complex forms. In the secondary fields, the received information is comprehended, it is recognized, the processes of perception of irritations of this modality are provided. From the secondary fields of individual sensory systems, information enters the posterior tertiary fields - the associative lower parietal zones, where the integration of signals of various modalities takes place, allowing you to create a complete image of the outside world with all its smells, sounds, colors, etc. Here, based on afferent messages from different parts of the right and left halves of the body, complex representations of a person are formed, about the scheme of space and the scheme of the body, which provide spatial orientation of movements and precise addressing of motor commands to various skeletal muscles. These zones are also of particular importance in storing the information received. Based on the analysis and synthesis of information processed in the posterior tertiary field of the cortex, all the anterior tertiary fields (anterior frontal region), goals, objectives and programs of human behavior are formed.

An important feature of the cortical organization of sensory systems is the screen or somatotopic (lat. somaticus bodily, topicus local) representation of functions. The sensitive cortical centers of the primary fields of the cortex form, as it were, a screen reflecting the location of the receptors on the periphery, i.e., there are point-to-point projections here. So, in the posterior central gyrus (general sensitive field) neurons of tactile, temperature and skin sensitivity presented in the same order as the receptors on the surface of the body, resembling a copy of a man (homunculus); in the visual cortex like a screen of retinal receptors; in the auditory cortex, in a certain order, neurons that respond to a certain pitch of sounds. The same principle of spatial representation of information is observed in the switching nuclei of the diencephalon, in the cerebellar cortex, which greatly facilitates the interaction of various parts of the central nervous system.

The area of ​​cortical sensory representation in its size reflects functional significance one or another piece of afferent information. Thus, due to the special significance of the analysis of information from the kinesthetic receptors of the fingers and from the speech-producing apparatus in humans, the territory of their cortical representation significantly exceeds the sensory representation of other parts of the body. Similarly, per unit area of ​​the fovea in the retina there is almost 500 times more area of ​​the visual cortex than the same unit area of ​​the periphery of the retina.

The higher departments of the central nervous system provide an active search for sensory information. This is clearly manifested in the activity of the visual sensory system. Special studies of eye movements have shown that the gaze captures not all points in space, but only the most informative features that are especially important for solving any problem at a given moment. The search function of the eyes is part of the active behavior of a person in the external environment, his conscious activity. It is controlled by the higher analyzing and integrating areas of the cortex - the frontal lobes, under the control of which there is an active perception of the external world.

The cerebral cortex provides the widest interaction of various sensory systems and their participation in the organization of human motor actions, including in the process of his sports activity.

The value of the activity of sensory systems in sports

The effectiveness of performing sports exercises largely depends on the processes of perception and processing of sensory information. These processes determine both the most rational organization of motor acts and the perfection of the athlete's tactical thinking. A clear perception of space and spatial orientation of movements are provided by the functioning of visual, auditory, vestibular, kinesthetic reception. Estimation of time intervals and control of time parameters of movements are based on proprioceptive and auditory sensations. Vestibular irritations during turns, rotations, tilts, etc. noticeably affect the coordination of movements and the manifestation of physical qualities, especially with low stability of the vestibular apparatus. Experimental switching off of individual sensory afferentations in athletes (performing movements in a special collar that excludes the activation of cervical proprioceptors; when using glasses that cover the central or peripheral field of vision) led to a sharp decrease in marks for the exercise or to the complete impossibility of its execution. In contrast to this, the communication to the athlete of additional information (especially urgent in the process of movement) helped to quickly improve technical actions. Based on the interaction of sensory systems, athletes develop complex representations that accompany their activities in their chosen sport - the “feeling” of ice, snow, water, etc. At the same time, in each sport there are the most important leading sensory systems, on the activity of which the success of an athlete's performance depends to the greatest extent.

Types of sensory systems

In [Mf20] highly developed animals, according to the presence of specialized receptors, they distinguish visual, auditory, vestibular, olfactory, gustatory, tactile and proprioceptive sensory systems, each of which includes specialized structures of the main departments of the central nervous system.

Representatives of various classes, orders of animals have one or two main sensory systems , with the help of which they receive basic information from the external environment [B21] .

However, as evolutionary development, the main role is assigned to the visual and auditory systems. These analyzers are called advanced sensory systems .

Their main role is reflected in their design. The visual and auditory systems have:

1. the most differentiated structure of the receptor apparatus,

2. a large number of brain structures receive impulses from visual and auditory input,

3. the largest number of cortical fields is occupied by the processing of acoustic and optical information,

4. In the structure of these systems, the management of the functioning of their individual structures with the help of feedbacks is developed.

5. The results of the functioning of these sensory systems are realized to the maximum extent.

Development second signal system in humans, it became possible due to the powerful development of neocortical formations of the frontal and parietotemporal lobes, which receive already processed visual, auditory and proprioceptive information.

The control of human behavior in the environment with the help of the second signal system determines the maximum development of progressive sensory systems.

With the development of progressive sensory systems, there is a suppression of the activity of more ancient sensory systems: olfactory, gustatory and vestibular.

General scheme of the structure of sensory systems

I.P. Pavlov distinguished 3 analyzer departments :

1. peripheral (set of receptors) ,

2. conductive (paths of excitation),

3. central (cortical neurons that analyze the stimulus)

The analyzer begins with receptors and ends with neurons that are connected by neurons in the motor areas of the cerebral cortex.

Do not confuse analyzers with reflex arcs. Analyzers do not have an effector part.

The main general principles for constructing sensory systems in higher vertebrates and humans are:

1. layering

2. multichannel

3. differentiation elements of the sensory system

3.1. horizontally

3.2. vertically

4. availability sensory funnels

4.1. tapering

4.2. expanding

Layering sensory system - the presence of several layers of nerve cells between the receptors and neurons of the motor areas of the cerebral cortex.

physiological meaning layering: this property allows the body to quickly respond to simple signals analyzed already at the first levels of the sensory system.

Conditions are also being created for the selective regulation of the properties of the neural layers by ascending influences from other parts of the brain.

Multichannel sensory system - the presence in each layer of many (from tens of thousands to millions) of nerve cells associated with many cells of the next layer, the presence of many parallel channels processing and transmission of information.

physiological meaning multichannel - providing the sensor system with reliability, accuracy and detail of signal analysis.

sensory funnels. A different number of elements in adjacent layers forms "sensor funnels". So, in the human retina there are 130 million photoreceptors, and in the ganglion cell layer of the retina there are 100 times fewer neurons - " tapering funnel ».

At the next levels of the visual system, « expanding funnel»: the number of neurons in the primary projection area of ​​the visual cortex is thousands of times greater than that of retinal ganglion cells.

In the auditory and in a number of other sensory systems, there is an "expanding funnel" from the receptors to the cerebral cortex.

physiological meaning The "shrinking funnel" is to reduce the redundancy of information, and the "expanding" one is to provide a fractional and complex analysis of various signal features;

Differentiationsensory system vertically - morphological and functional difference between different layers of the sensory system [B22] .

According to Pokrovsky, the vertical differentiation of the sensory system consists in the formation of departments, each of which consists of several neural layers. Thus, a department is a larger morphofunctional formation than a layer of neurons. Each department (for example, olfactory bulbs, cochlear nuclei of the auditory system or geniculate bodies) performs a specific function.

Differentiationsensory system horizontally - the difference in the morphological and physiological properties of receptors, neurons and connections between them within each of the layers.

So, in the visual analyzer there are two parallel neural channels running from photoreceptors to the cerebral cortex and processing information coming from the center and from the periphery of the retina in different ways.

The main functions (operations) of the sensor system:

1. detection;

2. distinction;

3. transfer and transformation;

4. coding;

5. feature detection;

6. pattern recognition.

Detection and primary discrimination of signals is provided by receptors, and detection and recognition of signals - by neurons of the cerebral cortex. Transmission, transformation and encoding of signals is carried out by neurons of all layers of sensory systems.

Sensor system (analyzer)- they call the part of the nervous system, consisting of perceiving elements - sensory receptors, nerve pathways that transmit information from receptors to the brain and parts of the brain that process and analyze this information

The sensory system includes 3 parts

1. Receptors - sense organs

2. Conductor section that connects receptors with the brain

3. Department of the cerebral cortex, which perceives and processes information.

Receptors- a peripheral link designed to perceive stimuli of the external or internal environment.

Sensor systems have a common structural plan and for sensory systems is characterized

Layering- the presence of several layers of nerve cells, the first of which is associated with receptors, and the last with neurons in the motor areas of the cerebral cortex. Neurons are specialized for processing different types of sensory information.

Multichannel- the presence of many parallel channels for processing and transmitting information, which provides a detailed signal analysis and greater reliability.

Different number of elements in adjacent layers, which forms the so-called "sensor funnels" (contracting or expanding) They can ensure the elimination of information redundancy or, conversely, a fractional and complex analysis of signal features

Differentiation of the sensory system vertically and horizontally. Vertical differentiation means the formation of parts of the sensory system, consisting of several neuronal layers (olfactory bulbs, cochlear nuclei, geniculate bodies).

Horizontal differentiation represents the presence of different properties of receptors and neurons within the same layer. For example, rods and cones in the retina of the eye process information differently.

The main task of the sensory system is the perception and analysis of the properties of stimuli, on the basis of which sensations, perceptions, and representations arise. This constitutes the forms of sensual, subjective reflection of the external world.

Functions of sensory systems

1. Signal detection. Each sensory system in the process of evolution has adapted to the perception of adequate stimuli inherent in this system. The sensory system, for example the eye, can receive different - adequate and inadequate irritations (light or a blow to the eye). Sensory systems perceive force - the eye perceives 1 light photon (10 V -18 W). Impact on the eye (10 V -4 W). Electric current(10V-11W)
2. Distinguishing signals.
3. Signal transmission or conversion. Any sensory system works like a transducer. It converts one form of energy of the acting stimulus into the energy of nervous irritation. The sensory system must not distort the stimulus signal.

• May be spatial
• Temporal transformations
• limitation of information redundancy (inclusion of inhibitory elements that inhibit neighboring receptors)
• Identification of essential features of a signal

1. Information encoding - in the form of nerve impulses
2. Signal detection, etc. e. highlighting signs of a stimulus that has behavioral significance
3. Provide image recognition
4. Adapt to stimuli
5. Interaction of sensory systems, which form the scheme of the surrounding world and at the same time allow us to correlate ourselves with this scheme, for our adaptation. All living organisms cannot exist without the perception of information from the environment. The more accurately the organism receives such information, the higher will be its chances in the struggle for existence.

Sensory systems are capable of responding to inappropriate stimuli. If you try the battery terminals, it causes a taste sensation - sour, this is the action of an electric current. Such a reaction of the sensory system to adequate and inadequate stimuli raised the question for physiology - how much we can trust our senses.

Johann Müller formulated in 1840 the law of the specific energy of the sense organs.

The quality of sensations does not depend on the nature of the stimulus, but is determined entirely by the specific energy inherent in the sensitive system, which is released under the action of the stimulus.

With this approach, we can only know what is inherent in ourselves, and not what is in the world around us. Subsequent studies have shown that excitations in any sensory system arise on the basis of one energy source - ATP.

Müller's student Helmholtz created symbol theory, according to which he considered sensations as symbols and objects of the surrounding world. The theory of symbols denied the possibility of knowing the surrounding world.

These 2 directions were called physiological idealism. What is sensation? Feeling is a subjective image of the objective world. Feelings are images of the external world. They exist in us and are generated by the action of things on our sense organs. For each of us, this image will be subjective, i.e. it depends on the degree of our development, experience, and each person perceives the surrounding objects and phenomena in his own way. They will be objective, i.e. that means they exist independently of our consciousness. Since there is a subjectivity of perception, how to decide who perceives most correctly? Where will the truth be? The criterion of truth is practical activity. There is gradual knowledge. At each stage, new information is obtained. The child tastes toys, disassembles them into details. It is on the basis of this profound experience that we acquire deeper knowledge about the world.

Classification of receptors.

1. Primary and secondary. primary receptors represent the receptor ending, which is formed by the very first sensitive neuron (Pacini's corpuscle, Meissner's corpuscle, Merkel's disc, Ruffini's corpuscle). This neuron lies in the spinal ganglion. Secondary receptors perceive information. Due to specialized nerve cells, which then transmit excitation to the nerve fiber. Sensitive cells of the organs of taste, hearing, balance.
2. Remote and contact. Some receptors perceive excitation with direct contact - contact, while others can perceive irritation at some distance - distant
3. Exteroreceptors, interoreceptors. Exteroreceptors- perceive irritation from the external environment - vision, taste, etc., and they provide for adaptation to the environment. Interoreceptors- receptors of internal organs. They reflect the state of the internal organs and the internal environment of the body.
4. Somatic - superficial and deep. Superficial - skin, mucous membranes. Deep - receptors of muscles, tendons, joints
5. Visceral
6. CNS receptors
7. Special sense receptors - visual, auditory, vestibular, olfactory, gustatory

By the nature of perception of information

1. Mechanoreceptors (skin, muscles, tendons, joints, internal organs)
2. Thermoreceptors (skin, hypothalamus)
3. Chemoreceptors (aortic arch, carotid sinus, medulla oblongata, tongue, nose, hypothalamus)
4. Photoreceptor (eye)
5. Pain (nociceptive) receptors (skin, internal organs, mucous membranes)

Mechanisms of excitation of receptors

In the case of primary receptors, the action of the stimulus is perceived by the ending of the sensitive neuron. An active stimulus can cause hyperpolarization or depolarization of the surface membrane of receptors, mainly due to changes in sodium permeability. An increase in the permeability to sodium ions leads to membrane depolarization and a receptor potential appears on the receptor membrane. It exists as long as the stimulus acts.

Receptor potential does not obey the law "All or nothing", its amplitude depends on the strength of the stimulus. It has no refractory period. This allows the receptor potentials to be summed up under the action of subsequent stimuli. It spreads meleno, with extinction. When the receptor potential reaches a critical threshold, it triggers an action potential at the nearest node of Ranvier. In the interception of Ranvier, an action potential arises, which obeys the law "All or Nothing". This potential will be propagating.

In the secondary receptor, the action of the stimulus is perceived by the receptor cell. In this cell, a receptor potential arises, which will result in the release of a mediator from the cell into the synapse, which acts on the postsynaptic membrane of the sensitive fiber and the interaction of the mediator with receptors leads to the formation of another, local potential, which is called generator. It is identical in its properties to the receptor. Its amplitude is determined by the amount of mediator released. Mediators - acetylcholine, glutamate.

Action potentials occur periodically, tk. they are characterized by a period of refractoriness, when the membrane loses the property of excitability. Action potentials arise discretely and the receptor in the sensory system works as an analog-to-discrete converter. In the receptors, an adaptation is observed - adaptation to the action of stimuli. Some are fast adapting and some are slow adapting. With adaptation, the amplitude of the receptor potential and the number of nerve impulses that go along the sensitive fiber decrease. Receptors encode information. It is possible by the frequency of potentials, by the grouping of impulses into separate volleys and by the intervals between volleys. Coding is possible according to the number of activated receptors in the receptive field.

Threshold of irritation and threshold of entertainment.

Irritation threshold- the minimum strength of the stimulus that causes a sensation.

Threshold entertainment- the minimum force of change in the stimulus, at which a new sensation arises.

Hair cells are excited when the hairs are displaced by 10 to -11 meters - 0.1 amstrem.

In 1934, Weber formulated a law that establishes a relationship between the initial strength of irritation and the intensity of sensation. He showed that the change in the strength of the stimulus is a constant value

∆I / Io = K Io=50 ∆I=52.11 Io=100 ∆I=104.2

Fechner determined that sensation is directly proportional to the logarithm of irritation.

S=a*logR+b S-sensation R- irritation

S \u003d KI in A degree I - the strength of irritation, K and A - constants

For tactile receptors S=9.4*I d 0.52

Sensory systems have receptors for self-regulation of receptor sensitivity.

Influence of the sympathetic system - the sympathetic system increases the sensitivity of receptors to the action of stimuli. This is useful in a situation of danger. Increases the excitability of receptors - the reticular formation. Efferent fibers were found in the composition of sensory nerves, which can change the sensitivity of receptors. There are such nerve fibers in the auditory organ.

Sensory hearing system

For most people living in a modern stop, hearing progressively declines. This happens with age. This is facilitated by environmental sound pollution - vehicles, discotheques, etc. Changes in hearing aid become irreversible. Human ears contain 2 sensitive organs. Hearing and balance. Sound waves propagate in the form of compressions and rarefaction in elastic media, and the propagation of sounds in dense media is better than in gases. Sound has 3 important properties - pitch or frequency, power or intensity and timbre. The pitch of the sound depends on the frequency of vibrations and the human ear perceives with a frequency of 16 to 20,000 Hz. With maximum sensitivity from 1000 to 4000 Hz.

The main frequency of the sound of the larynx of a man is 100 Hz. Women - 150 Hz. When talking, additional high-frequency sounds appear in the form of hissing, whistling, which disappear when talking on the phone and this makes speech clearer.

The sound power is determined by the amplitude of the vibrations. Sound power is expressed in dB. Power is a logarithmic relationship. Whispered speech - 30 dB, normal speech - 60-70 dB. The sound of transport - 80, the noise of the aircraft engine - 160. The sound power of 120 dB causes discomfort, and 140 leads to pain.

The timbre is determined by secondary vibrations on sound waves. Ordered vibrations - create musical sounds. Random vibrations just cause noise. The same note sounds differently on different instruments due to different additional vibrations.

The human ear has 3 parts - outer, middle and inner ear. The outer ear is represented by the auricle, which acts as a sound-catching funnel. The human ear picks up sounds less perfectly than that of a rabbit, a horse that can control its ears. At the base of the auricle is cartilage, with the exception of the earlobe. Cartilage gives elasticity and shape to the ear. If the cartilage is damaged, then it is restored by growing. The external auditory canal is S-shaped - inward, forward and downward, length 2.5 cm. The auditory meatus is covered with skin with low sensitivity of the outer part and high sensitivity of the inner part. There are hairs on the outside of the ear canal that prevent particles from entering the ear canal. The ear canal glands produce a yellow lubricant that also protects the ear canal. At the end of the passage is the tympanic membrane, which consists of fibrous fibers covered on the outside with skin and inside with mucous. The eardrum separates the middle ear from the outer ear. It fluctuates with the frequency of the perceived sound.

The middle ear is represented by the tympanic cavity, the volume of which is approximately 5-6 drops of water and the tympanic cavity is filled with air, lined with a mucous membrane and contains 3 auditory ossicles: the hammer, anvil and stirrup. The middle ear communicates with the nasopharynx using the Eustachian tube. At rest, the lumen of the Eustachian tube is closed, which equalizes the pressure. Inflammatory processes leading to inflammation of this tube cause a feeling of congestion. The middle ear is separated from the inner ear by an oval and round opening. The vibrations of the tympanic membrane are transmitted through the system of levers by the stirrup to the oval window, and the outer ear transmits sounds by air.

There is a difference in the area of ​​the tympanic membrane and the oval window (the area of ​​the tympanic membrane is 70 mm square, and that of the oval window is 3.2 mm square). When vibrations are transmitted from the membrane to the oval window, the amplitude decreases and the strength of the vibrations increases by 20-22 times. At frequencies up to 3000 Hz, 60% of E is transmitted to the inner ear. In the middle ear there are 2 muscles that change vibrations: the tensor tympanic membrane muscle (attached to the central part of the tympanic membrane and to the handle of the malleus) - with an increase in contraction force, the amplitude decreases; stirrup muscle - its contractions limit the movement of the stirrup. These muscles prevent injury to the eardrum. In addition to air transmission of sounds, there is also bone transmission, but this sound power is not able to cause vibrations of the bones of the skull.

inside ear

the inner ear is a maze of interconnected tubes and extensions. The organ of balance is located in the inner ear. The labyrinth has a bone base, and inside there is a membranous labyrinth and there is an endolymph. The cochlea belongs to the auditory part, it forms 2.5 turns around the central axis and is divided into 3 ladders: vestibular, tympanic and membranous. The vestibular canal begins with the membrane of the oval window and ends with a round window. At the apex of the cochlea, these 2 canals communicate with a helicocream. And both of these canals are filled with perilymph. The organ of Corti is located in the middle membranous canal. The main membrane is built from elastic fibers that start at the base (0.04mm) and reach the top (0.5mm). To the top, the density of the fibers decreases by 500 times. The organ of Corti is located on the main membrane. It is built from 20-25 thousand special hair cells located on supporting cells. Hair cells lie in 3-4 rows (outer row) and in one row (inner). At the top of the hair cells are stereociles or kinocilies, the largest stereociles. Sensory fibers of the 8th pair of cranial nerves from the spiral ganglion approach the hair cells. At the same time, 90% of the isolated sensitive fibers end up on the inner hair cells. Up to 10 fibers converge per inner hair cell. And in the composition of nerve fibers there are also efferent ones (olive-cochlear bundle). They form inhibitory synapses on sensory fibers from the spiral ganglion and innervates the outer hair cells. Irritation of the organ of Corti is associated with the transmission of vibrations of the bones to the oval window. Low-frequency vibrations propagate from the oval window to the top of the cochlea (the entire main membrane is involved). At low frequencies, excitation of the hair cells lying on the top of the cochlea is observed. Bekashi studied the propagation of waves in a cochlea. He found that as the frequency increased, a smaller column of liquid was drawn in. High-frequency sounds cannot involve the entire fluid column, so the higher the frequency, the less the perilymph fluctuates. Oscillations of the main membrane can occur during the transmission of sounds through the membranous canal. When the main membrane oscillates, the hair cells move upward, which causes depolarization, and if downward, the hairs deviate inward, which leads to hyperpolarization of the cells. When hair cells depolarize, Ca channels open and Ca promotes an action potential that carries information about the sound. The outer auditory cells have efferent innervation and the transmission of excitation occurs with the help of Ash on the outer hair cells. These cells can change their length: they shorten during hyperpolarization and elongate during polarization. Changing the length of the outer hair cells affects the oscillatory process, which improves the perception of sound by the inner hair cells. The change in the potential of hair cells is associated with the ionic composition of the endo- and perilymph. Perilymph resembles CSF, and endolymph has a high concentration of K (150 mmol). Therefore, the endolymph acquires a positive charge to the perilymph (+80mV). Hair cells contain a lot of K; they have a membrane potential and are negatively charged inside and positive outside (MP = -70mV), and the potential difference makes it possible for K to penetrate from the endolymph into the hair cells. Changing the position of one hair opens 200-300 K-channels and depolarization occurs. Closure is accompanied by hyperpolarization. In the organ of Corti, frequency coding occurs due to the excitation of different parts of the main membrane. At the same time, it was shown that low-frequency sounds can be encoded by the same number of nerve impulses as the sound. Such coding is possible with the perception of sound up to 500 Hz. Encoding of sound information is achieved by increasing the number of volleys of fibers for a more intense sound and due to the number of activated nerve fibers. The sensory fibers of the spiral ganglion terminate in the dorsal and ventral nuclei of the cochlea of ​​the medulla oblongata. From these nuclei, the signal enters the olive nuclei of both its own and the opposite side. From its neurons there are ascending paths as part of the lateral loop that approach the inferior colliculus of the quadrigemina and the medial geniculate body of the thalamus opticus. From the latter, the signal goes to the superior temporal gyrus (Geshl gyrus). This corresponds to fields 41 and 42 (primary zone) and field 22 (secondary zone). In the CNS, there is a topotonic organization of neurons, that is, sounds are perceived with different frequencies and different intensities. The cortical center is important for perception, sound sequence and spatial localization. With the defeat of the 22nd field, the definition of words is violated (receptive opposition).

The nuclei of the superior olive are divided into medial and lateral parts. And the lateral nuclei determine the unequal intensity of sounds coming to both ears. The medial nucleus of the superior olive picks up temporal differences in the arrival of sound signals. It was found that signals from both ears enter different dendritic systems of the same perceiving neuron. Hearing impairment can be manifested by ringing in the ears when the inner ear or auditory nerve is irritated, and two types of deafness: conductive and nervous. The first is associated with lesions of the outer and middle ear (wax plug). The second is associated with defects in the inner ear and lesions of the auditory nerve. Elderly people lose the ability to perceive high-pitched voices. Due to the two ears, it is possible to determine the spatial localization of sound. This is possible if the sound deviates from the middle position by 3 degrees. When perceiving sounds, it is possible to develop adaptation due to the reticular formation and efferent fibers (by acting on the outer hair cells.

visual system.

Vision is a multi-link process that begins with the projection of an image onto the retina of the eye, then there is excitation of photoreceptors, transmission and transformation in the neural layers of the visual system, and ends with the decision of the higher cortical sections about the visual image.

The structure and functions of the optical apparatus of the eye. The eye has a spherical shape, which is important for turning the eye. Light passes through several transparent media - the cornea, lens and vitreous body, which have certain refractive powers, expressed in diopters. The diopter is equal to the refractive power of a lens with a focal length of 100 cm. The refractive power of the eye when viewing distant objects is 59D, close ones is 70.5D. An inverted image is formed on the retina.

Accommodation- adaptation of the eye to a clear vision of objects at different distances. The lens plays a major role in accommodation. When considering close objects, the ciliary muscles contract, the ligament of zinn relaxes, the lens becomes more convex due to its elasticity. When considering distant ones, the muscles are relaxed, the ligaments are stretched and stretch the lens, making it more flattened. The ciliary muscles are innervated by parasympathetic fibers of the oculomotor nerve. Normally, the farthest point of clear vision is at infinity, the nearest one is 10 cm from the eye. The lens loses elasticity with age, so the nearest point of clear vision moves away and senile farsightedness develops.

Refractive anomalies of the eye.

Nearsightedness (myopia). If the longitudinal axis of the eye is too long or the refractive power of the lens increases, then the image is focused in front of the retina. The person can't see well. Spectacles with concave lenses are prescribed.

Farsightedness (hypermetropia). It develops with a decrease in the refractive media of the eye or with a shortening of the longitudinal axis of the eye. As a result, the image is focused behind the retina and the person has trouble seeing nearby objects. Spectacles with convex lenses are prescribed.

Astigmatism is the uneven refraction of rays in different directions, due to the non-strictly spherical surface of the cornea. They are compensated by glasses with a surface approaching a cylindrical one.

Pupil and pupillary reflex. The pupil is the hole in the center of the iris through which light rays pass into the eye. The pupil improves the clarity of the image on the retina by increasing the depth of field of the eye and by eliminating spherical aberration. If you cover your eye from the light, and then open it, the pupil quickly narrows - the pupillary reflex. In bright light, the size is 1.8 mm, with an average - 2.4, in the dark - 7.5. Zooming in results in poorer image quality, but increases sensitivity. The reflex has an adaptive value. The sympathetic pupil dilates, the parasympathetic pupil narrows. In healthy people, the size of both pupils is the same.

Structure and functions of the retina. The retina is the inner light-sensitive membrane of the eye. Layers:

Pigmentary - a row of process epithelial cells of black color. Functions: shielding (prevents scattering and reflection of light, increasing clarity), regeneration of visual pigment, phagocytosis of fragments of rods and cones, nutrition of photoreceptors. The contact between the receptors and the pigment layer is weak, so it is here that retinal detachment occurs.

Photoreceptors. Flasks are responsible for color vision, there are 6-7 million of them. Sticks for twilight, there are 110-123 million of them. They are unevenly located. In the central fovea - only flasks, here - the greatest visual acuity. Sticks are more sensitive than flasks.

The structure of the photoreceptor. It consists of an outer receptive part - the outer segment, with a visual pigment; connecting leg; nuclear part with a presynaptic ending. The outer part consists of disks - a two-membrane structure. The outdoor segments are constantly updated. The presynaptic terminal contains glutamate.

visual pigments. In sticks - rhodopsin with absorption in the region of 500 nm. In flasks - iodopsin with absorptions of 420 nm (blue), 531 nm (green), 558 (red). The molecule consists of the protein opsin and the chromophore part - retinal. Only the cis-isomer perceives light.

Physiology of photoreception. Upon absorption of a quantum of light, cis-retinal turns into trans-retinal. This causes spatial changes in the protein part of the pigment. The pigment becomes colorless and transforms into metarhodopsin II, which is able to interact with the membrane-bound protein transducin. Transducin is activated and binds to GTP, activating phosphodiesterase. PDE destroys cGMP. As a result, the concentration of cGMP falls, which leads to the closure of ion channels, while the concentration of sodium decreases, leading to hyperpolarization and the appearance of a receptor potential that spreads throughout the cell to the presynaptic terminal and causes a decrease in glutamate release.

Restoration of the initial dark state of the receptor. When metarhodopsin loses its ability to interact with tranducine, guanylate cyclase, which synthesizes cGMP, is activated. Guanylate cyclase is activated by a drop in the concentration of calcium ejected from the cell by the exchange protein. As a result, the concentration of cGMP rises and it again binds to the ion channel, opening it. When opening, sodium and calcium enter the cell, depolarizing the receptor membrane, turning it into a dark state, which again accelerates the release of the mediator.

retinal neurons.

Photoreceptors are synaptically connected to bipolar neurons. Under the action of light on the neurotransmitter, the release of the mediator decreases, which leads to hyperpolarization of the bipolar neuron. From the bipolar signal is transmitted to the ganglion. Impulses from many photoreceptors converge to a single ganglion neuron. The interaction of neighboring retinal neurons is provided by horizontal and amacrine cells, the signals of which change the synaptic transmission between receptors and bipolar (horizontal) and between bipolar and ganglionic (amacrine). Amacrine cells carry out lateral inhibition between adjacent ganglion cells. The system also contains efferent fibers that act on synapses between bipolar and ganglion cells, regulating the excitation between them.

Nerve pathways.

1st neuron is bipolar.

2nd - ganglionic. Their processes are in the composition optic nerve, make a partial crossover (necessary to provide each hemisphere with information from each eye) and go to the brain as part of the visual tract, getting into the lateral geniculate body of the thalamus (3rd neuron). From the thalamus - to the projection zone of the cortex, the 17th field. Here is the 4th neuron.

visual functions.

Absolute sensitivity. For the appearance of a visual sensation, it is necessary that the light stimulus has a minimum (threshold) energy. The stick can be excited by one quantum of light. Sticks and flasks differ little in excitability, but the number of receptors that send signals to one ganglion cell is different in the center and on the periphery.

Visual adaptation.

Adaptation of the visual sensory system to conditions of bright illumination - light adaptation. The reverse phenomenon is dark adaptation. The increase in sensitivity in the dark is gradual, due to the dark restoration of visual pigments. First, iodopsin flasks are reconstituted. It has little effect on sensitivity. Then the rhodopsin of the sticks is restored, which greatly increases the sensitivity. For adaptation, the processes of changing connections between retinal elements are also important: weakening of horizontal inhibition, leading to an increase in the number of cells, sending signals to the ganglion neuron. The influence of the CNS also plays a role. When illuminating one eye, it lowers the sensitivity of the other.

Differential visual sensitivity. According to Weber's law, a person will distinguish a difference in lighting if it is stronger by 1-1.5%.

Brightness Contrast occurs due to mutual lateral inhibition of optic neurons. A gray stripe on a light background appears darker than a gray one on a dark one, since the cells excited by the light background inhibit the cells excited by the gray stripe.

Blinding brightness of light. Light that is too bright causes an unpleasant sensation of blinding. The upper limit of blinding brightness depends on the adaptation of the eye. The longer the dark adaptation was, the less brightness causes glare.

Vision inertia. Visual sensation appears and disappears immediately. From irritation to perception, 0.03-0.1 s passes. The stimuli quickly following one another merge into one sensation. The minimum frequency of repetition of light stimuli, at which the fusion of individual sensations occurs, is called the critical frequency of flicker fusion. This is what cinema is based on. Sensations that continue after the cessation of irritation are sequential images (the image of a lamp in the dark after it is turned off).

Color vision.

The entire visible spectrum from violet (400nm) to red (700nm).

Theories. Three-component theory of Helmholtz. Color sensation provided by three types of bulbs sensitive to one part of the spectrum (red, green or blue).

Goering's theory. The flasks contain substances sensitive to white-black, red-green and yellow-blue radiation.

Consistent color images. If you look at a painted object and then at a white background, the background will acquire an additional color. The reason is color adaptation.

Color blindness. Color blindness is a disorder in which it is impossible to distinguish colors. With protanopia, red color is not distinguished. With deuteranopia - green. With tritanopia - blue. Diagnosed by polychromatic tables.

A complete loss of color perception is achromasia, in which everything is seen in shades of gray.

Perception of space.

Visual acuity- the maximum ability of the eye to distinguish individual details of objects. The normal eye distinguishes between two points seen at an angle of 1 minute. Maximum sharpness in the region of the macula. Determined by special tables.

The concept of sensory systems was formulated by I.P. Pavlov in the doctrine of analyzers in 1909 during his study of higher nervous activity. Analyzer- a set of central and peripheral formations that perceive and analyze changes in the external and internal environments of the body. concept sensor system, which appeared later, replaced the concept of the analyzer, including the mechanisms of regulation of its various departments with the help of direct and feedback links. Along with this, there is still the concept sense organ as a peripheral entity that perceives and partially analyzes environmental factors. The main part of the sense organ are receptors, equipped with auxiliary structures that provide optimal perception. Thus, the organ of vision consists of the eyeball, the retina, which contains visual receptors, and a number of auxiliary structures: eyelids, muscles, lacrimal apparatus. The organ of hearing consists of the outer, middle and inner ear, where, in addition to the spiral (Corti) organ and its hair (receptor) cells, there are also a number of auxiliary structures. The tongue is the organ of taste. Under the direct influence of various environmental factors with the participation of analyzers in the body, Feel, which are reflections of the properties of objects of the objective world. The peculiarity of sensations is their modality, those. a set of sensations provided by any one analyzer. Within each modality, according to the type (quality) of the sensory impression, different qualities can be distinguished, or valency. Modalities are, for example, sight, hearing, taste. Qualitative types of modality (valency) for vision are various colors, for taste - the sensation of sour, sweet, salty, bitter.

The activity of analyzers is usually associated with the emergence of five senses - sight, hearing, taste, smell and touch, through which the body is connected with the external environment. However, in reality, there are much more of them. For example, the sense of touch in a broad sense, in addition to tactile sensations arising from touch, includes a sense of pressure and vibration. The temperature sensation includes sensations of heat or cold, but there are also more complex sensations, such as sensations of hunger, thirst, sexual desire (libido), due to a special (motivational) state of the body. The sensation of the position of the body in space is associated with the activity of the vestibular, motor analyzers and their interaction with the visual analyzer. A special place in the sensory function is occupied by the sensation of pain. In addition, we can, although "vaguely", perceive other changes, not only in the external, but also in the internal environment of the body, while emotionally colored sensations are formed. Yes, coronary spasm initial stage diseases, when pain does not yet arise, can cause a feeling of melancholy, despondency. Thus, the structures that perceive irritation from the environment and the internal environment of the body are actually much larger than is commonly believed.

The classification of analyzers can be based on various signs: the nature of the acting stimulus, the nature of the sensations that arise, the level of sensitivity of receptors, the speed of adaptation, and much more.

But the most significant is the classification of analyzers, which is based on their purpose (role). In this regard, there are several types of analyzers.

External analyzers perceive and analyze changes in the external environment. This should include visual, auditory, olfactory, gustatory, tactile and temperature analyzers, the excitation of which is perceived subjectively in the form of sensations.

Internal (visceral) analyzers, perceiving and analyzing changes in the internal environment of the body, indicators of homeostasis. Fluctuations in the indicators of the internal environment within the physiological norm in healthy person usually not perceived subjectively as sensations. So, we cannot subjectively determine the value of blood pressure, especially if it is normal, the state of the sphincters, etc. However, information coming from the internal environment plays an important role in regulating the functions of internal organs, ensuring the adaptation of the body to various conditions of its life. The significance of these analyzers is studied in the course of physiology (adaptive regulation of the activity of internal organs). But at the same time, a change in some constants of the internal environment of the body can be perceived subjectively in the form of sensations (thirst, hunger, sexual desire) that are formed on the basis of biological needs. To meet these needs, behavioral responses are included. For example, when a feeling of thirst arises due to the excitation of osmo- or volumic receptors, behavior is formed that is aimed at finding and taking water.

Body position analyzers perceive and analyze changes in the position of the body in space and body parts relative to each other. These include vestibular and motor (kinesthetic) analyzers. As we evaluate the position of our body or its parts relative to each other, this impulse reaches our consciousness. This is evidenced, in particular, by the experience of D. Maklosky, which he set on himself. Primary afferent fibers from muscle receptors were irritated by threshold electrical stimuli. An increase in the frequency of impulses of these nerve fibers evoked subjective sensations in the subject of a change in the position of the corresponding limb, although its position did not actually change.

Pain analyzer should be singled out separately in connection with its special significance for the body - it carries information about damaging effects. Pain can occur with irritation of both extero- and interoreceptors.

Structural and functional organization of analyzers

According to I.P. Pavlov (1909), any analyzer has three sections: peripheral, conductive and central, or cortical. The peripheral section of the analyzer is represented by receptors. Its purpose is the perception and primary analysis of changes in the external and internal environments of the body. In receptors, the stimulus energy is transformed into a nerve impulse, as well as signal amplification due to the internal energy of metabolic processes. Receptors are characterized by specificity (modality), i.e. the ability to perceive a certain type of stimulus to which they have adapted in the process of evolution (adequate stimuli), on which the primary analysis is based. So, the receptors of the visual analyzer are adapted to the perception of light, and the auditory receptors are adapted to sound, etc. That part of the receptor surface from which one afferent fiber receives a signal is called its receptive field. Receptive fields can have a different number of receptor formations (from 2 to 30 or more), among which there is a leader receptor, and overlap each other. The latter provides greater reliability of the function and plays a significant role in compensation mechanisms.

Receptors are characterized by great diversity.

In classification receptors the central place is occupied by their division depending on the type of perceived stimulus. There are five types of such receptors.

1. Mechanoreceptors are excited during their mechanical deformation, they are located in the skin, blood vessels, internal organs, musculoskeletal system, auditory and vestibular systems.

2. Chemoreceptors perceive chemical changes in the external and internal environment of the body. These include taste and olfactory receptors, as well as receptors that respond to changes in the composition of blood, lymph, intercellular and cerebrospinal fluid (changes in O 2 and CO 2 voltage, osmolarity and pH, glucose levels and other substances). Such receptors are found in the mucous membrane of the tongue and nose, the carotid and aortic bodies, the hypothalamus, and the medulla oblongata.

3. Thermoreceptors perceive temperature changes. They are divided into heat and cold receptors and are found in the skin, mucous membranes, blood vessels, internal organs, hypothalamus, middle, medulla and spinal cord.

4. Photoreceptors in the retina of the eye perceive light (electromagnetic) energy.

5. Nociceptors, the excitation of which is accompanied by pain sensations (pain receptors). These receptors are irritated by mechanical, thermal and chemical (histamine, bradykinin, K+, H+, etc.) factors. Painful stimuli are perceived by free nerve endings that are found in the skin, muscles, internal organs, dentin, and blood vessels.

From a psychophysiological point of view Receptors are divided according to the sense organs and the sensations formed into visual, auditory, gustatory, olfactory and tactile.

Location in the body Receptors are divided into extero- and interoreceptors.

Exteroreceptors include receptors of the skin, visible mucous membranes and sensory organs: visual, auditory, gustatory, olfactory, tactile, pain and temperature. Interoreceptors include receptors of internal organs (visceroreceptors), vessels and the central nervous system. A variety of interoreceptors are receptors of the musculoskeletal system (proprioreceptors) and vestibular receptors. If the same type of receptors (for example, chemoreceptors sensitive to CO 3) is localized both in the central nervous system (in the medulla oblongata) and in other places (vessels), then such receptors are divided into central and peripheral.

According to the speed of adaptation Receptors are divided into three groups: rapidly adapting (phasic), slowly adapting (tonic) and mixed (phasic-tonic), adapting at an average speed. Examples of rapidly adapting receptors are the receptors for vibration (Pacini corpuscles) and touch (Meissner corpuscles) on the skin. Slowly adapting receptors include proprioceptors, lung stretch receptors, and pain receptors. Retinal photoreceptors and skin thermoreceptors adapt at an average speed.

By structural and functional organization distinguish between primary and secondary receptors. Primary receptors are sensitive endings of the dendrite of the afferent neuron. The body of the neuron is located in the spinal ganglion or in the ganglion of the cranial nerves. In the primary receptor, the stimulus acts directly on the endings of the sensory neuron. Primary receptors are phylogenetically more ancient structures, they include olfactory, tactile, temperature, pain receptors and proprioceptors.

In the secondary receptors there is a special cell synaptically connected to the end of the dendrite of the sensory neuron. This is a cell, such as a photoreceptor, of epithelial nature or neuroectodermal origin.

This classification allows us to understand how the excitation of receptors occurs.

The mechanism of excitation of receptors. When a stimulus acts on a receptor cell in the protein-lipid layer of the membrane, a change in the spatial configuration of protein receptor molecules occurs. This leads to a change in the permeability of the membrane for certain ions, most often for sodium ions, but in last years the role of potassium in this process has also been discovered. Ion currents arise, the membrane charge changes, and the receptor potential (RP) is generated. And then the excitation process proceeds in different receptors in different ways. In the primary sensory receptors, which are free bare endings of a sensitive neuron (olfactory, tactile, proprioceptive), RP acts on the neighboring, most sensitive areas of the membrane, where an action potential (AP) is generated, which then propagates in the form of impulses along the nerve fiber. The conversion of external stimulus energy into AP in primary receptors can occur either directly on the membrane or with the participation of some auxiliary structures. So, for example, occurs in the body of Pacini. The receptor here is represented by the bare end of the axon, which is surrounded by a connective tissue capsule. When squeezing the Pacinian corpuscle, RP is recorded, which is further converted into an impulse response of the afferent fiber. In secondary sensory receptors, which are represented by specialized cells (visual, auditory, gustatory, vestibular), RP leads to the formation and release of the mediator from the presynaptic section of the receptor cell into the synaptic cleft of the receptor-afferent synapse. This mediator acts on the postsynaptic membrane of the sensitive neuron, causes its depolarization and the formation of a postsynaptic potential, which is called the generator potential (GP). GP, acting on the extrasynaptic regions of the membrane of the sensitive neuron, causes the generation of AP. GP can be both de- and hyperpolarization and, accordingly, cause excitation or inhibit the impulse response of the afferent fiber.

Properties and features of receptor and generator potentials

Receptor and generator potentials are bioelectrical processes that have the properties of a local or local response: they propagate with a decrement, i.e. with damping; the value depends on the strength of the irritation, since they obey the "law of force"; the value depends on the rate of increase of the stimulus amplitude in time; are capable of summing up when applying quickly following each other irritations.

So, in the receptors, the stimulus energy is converted into a nerve impulse, i.e. primary coding of information, transformation of information into a sensory code.

Most of the receptors have the so-called background activity, i.e. in them there is excitation in the absence of any irritants.

Conductor section of the analyzer includes afferent (peripheral) and intermediate neurons of the stem and subcortical structures of the central nervous system (CNS), which form, as it were, a chain of neurons located in different layers at each level of the CNS. The conductor section provides for the conduction of excitation from receptors to the cerebral cortex and partial processing of information. The conduction of excitation along the conduction section is carried out in two afferent ways:

1) by a specific projection path (direct afferent paths) from the receptor along strictly designated specific paths with switching at different levels of the central nervous system (at the level of the spinal cord and medulla oblongata, in the visual tubercles and in the corresponding projection zone of the cerebral cortex);

2) in a non-specific way, with the participation of the reticular formation. At the level of the brainstem, collaterals depart from a specific path to the cells of the reticular formation, to which various afferent excitations can converge, ensuring the interaction of analyzers. In this case, afferent excitations lose their specific properties (sensory modality) and change the excitability of cortical neurons. Excitation is conducted slowly through a large number of synapses. Due to the collaterals, the hypothalamus and other parts of the limbic system of the brain, as well as the motor centers, are included in the excitation process. All this provides the vegetative, motor and emotional components of sensory reactions.

Central, or cortical, analyzer department, according to I.P. Pavlov, consists of two parts: the central part, i.e. "nucleus", represented by specific neurons that process afferent impulses from receptors, and the peripheral part, i.e. "scattered elements" - neurons dispersed throughout the cerebral cortex. The cortical ends of the analyzers are also called "sensory zones", which are not strictly limited areas, they overlap each other. Currently, in accordance with cytoarchitectonic and neurophysiological data, projection (primary and secondary) and associative tertiary zones bark. Excitation from the corresponding receptors to the primary zones is directed along fast-conducting specific pathways, while the activation of secondary and tertiary (associative) zones occurs along polysynaptic non-specific pathways. In addition, the cortical zones are interconnected by numerous associative fibers. Neurons are unevenly distributed throughout the thickness of the cortex and usually form six layers. The main afferent pathways to the cortex end on the neurons of the upper layers (III - IV). These layers are most strongly developed in the central sections of the visual, auditory and skin analyzers. Afferent impulses involving the stellate cells of the cortex (layer IV) are transmitted to pyramidal neurons (layer III), from here the processed signal leaves the cortex to other brain structures.

In the cortex, the input and output elements, together with stellate cells, form the so-called columns - functional units of the cortex, organized in the vertical direction. The column has a diameter of about 500 µm and is defined by the area of ​​distribution of collaterals of the ascending afferent thalamocortical fiber. Neighboring columns have relationships that organize the participation of multiple columns for the implementation of a particular reaction. The excitation of one of the columns leads to the inhibition of the neighboring ones.

Cortical projections of sensory systems have a topical principle of organization. The volume of the cortical projection is proportional to the density of the receptors. Due to this, for example, the central fovea of ​​the retina in the cortical projection is represented by a larger area than the periphery of the retina.

To determine the cortical representation of various sensory systems, the method of registration of evoked potentials (EP) is used. EP is one of the types of induced electrical activity in the brain. Sensory EPs are recorded during stimulation of receptor formations and are used to characterize such an important function as perception.

From general principles organization of analyzers should highlight multi-level and multi-channel.

Multilevel provides the possibility of specialization of different levels and layers of the CNS for the processing of certain types of information. This allows the body to respond more quickly to simple signals that are already analyzed at separate intermediate levels.

The existing multichannel nature of analyzer systems is manifested in the presence of parallel neural channels, i.e. in the presence in each of the layers and levels of a plurality of nerve elements associated with a plurality of nerve elements of the next layer and level, which in turn transmit nerve impulses to elements of a higher level, thereby ensuring the reliability and accuracy of the analysis of the influencing factor.

At the same time, existing hierarchical principle building sensory systems creates conditions for fine regulation of perception processes through influences from higher levels to lower ones.

These structural features central department ensure the interaction of various analyzers and the process of compensating for impaired functions. At the level of the cortical section, the highest analysis and synthesis of afferent excitations is carried out, providing a complete picture of the environment.

The main properties of analyzers are as follows.

1. High sensitivity to an adequate stimulus. All parts of the analyzer, and above all the receptors, are highly excitable. Thus, retinal photoreceptors can be excited by the action of only a few photons of light, olfactory receptors inform the body about the appearance of single molecules of odorous substances. However, when considering this property of the analyzers, it is preferable to use the term "sensitivity" rather than "excitability", since in humans it is determined by the appearance of sensations.

Sensitivity is assessed using a number of criteria.

Threshold of sensation(absolute threshold) - the minimum strength of irritation that causes such excitation of the analyzer, which is perceived subjectively in the form of a sensation.

Discrimination Threshold(differential threshold) - the minimum change in the strength of the acting stimulus, perceived subjectively in the form of a change in the intensity of sensation. This pattern was established by E. Weber in an experiment with determining the force of pressure on the palm by the test subjects. It turned out that under the action of a load of 100 g it was necessary to add a load of 3 g to feel the increase in pressure, with a load of 200 g it was necessary to add 6 g, 400 g - 12 g, etc. In this case, the ratio of the increase in the strength of irritation (L) to the strength of the acting stimulus (L) is a constant value (C):

For different analyzers, this value is different, in this case it is approximately 1/30 of the strength of the acting stimulus. A similar pattern is observed with a decrease in the strength of the acting stimulus.

Feeling intensity with the same strength of the stimulus, it can be different, since it depends on the level of excitability of the various structures of the analyzer at all its levels. This pattern was studied by G. Fechner, who showed that the intensity of sensation is directly proportional to the logarithm of the strength of stimulation. This position is expressed by the formula:

where E is the intensity of sensations,

K is a constant,

L is the strength of the acting stimulus,

L 0 - sensation threshold (absolute threshold).

Weber's and Fechner's laws are not accurate enough, especially at low stimulation strength. Psychophysical research methods, although they suffer from some inaccuracy, are widely used in the study of analyzers in practical medicine, for example, in determining visual acuity, hearing, smell, tactile sensitivity, and taste.

2. inertia- relatively slow emergence and disappearance of sensations. The latent time of the appearance of sensations is determined by the latent period of excitation of receptors and the time required for the transition of excitation in synapses from one neuron to another, the time of excitation of the reticular formation and generalization of excitation in the cerebral cortex. Preservation for a certain period of sensations after the stimulus is turned off is explained by the phenomenon of aftereffect in the central nervous system - mainly by the circulation of excitation. Thus, a visual sensation does not arise and does not disappear instantly. The latent period of visual sensation is 0.1 s, the aftereffect time is 0.05 s. Light stimuli (flickering) rapidly following one after another can give a sensation of continuous light (the phenomenon of "flicker merging"). The maximum frequency of flashes of light, which are still perceived separately, is called the critical flicker frequency, which is the greater, the stronger the stimulus brightness and the higher the excitability of the central nervous system, and is about 20 flickers per second. Along with this, if two motionless stimuli are successively projected at different parts of the retina with an interval of 20–200 ms, a sensation of the movement of the object arises. This phenomenon is called "Phi-phenomena". This effect is observed even when one stimulus is somewhat different in form from another. These two phenomena, "flicker fusion" and "Phi-phenomenon" are at the heart of cinematography. Due to the inertia of perception, the visual sensation from one frame lasts until the appearance of another, which is why the illusion of continuous movement arises. Typically, this effect occurs with the rapid sequential presentation of still images on the screen at a speed of 18-24 frames per second.

3. Ability sensory system to adaptation at a constant strength of a long-acting stimulus, it consists mainly in a decrease in absolute and an increase in differential sensitivity. This property is inherent in all parts of the analyzer, but it manifests itself most clearly at the level of receptors and consists in a change not only in their excitability and impulsation, but also in indicators of functional mobility, i.e. in changing the number of functioning receptor structures (P.G. Snyakin). According to the rate of adaptation, all receptors are divided into quickly and slowly adapting, sometimes a group of receptors with an average rate of adaptation is also distinguished. In the conductive and cortical sections of the analyzers, adaptation is manifested in a decrease in the number of activated fibers and nerve cells.

An important role in sensory adaptation is played by efferent regulation, which is carried out by descending influences that change the activity of the underlying structures of the sensory system. Due to this, the phenomenon of "tuning" of sensory systems to the optimal perception of stimuli in a changed environment arises.

4. Interaction of analyzers. With the help of analyzers, the body learns the properties of objects and phenomena of the environment, the beneficial and negative aspects of their impact on the body. Therefore, violations of the function of external analyzers, especially visual and auditory, make it extremely difficult to understand the outside world (the surrounding world is very poor for the blind or deaf). However, only analytical processes in the CNS cannot create a real idea of ​​the environment. The ability of analyzers to interact with each other provides a figurative and holistic view of the objects of the outside world. For example, we evaluate the quality of a lemon wedge using visual, olfactory, tactile and taste analyzers. At the same time, an idea is formed both about individual qualities - color, consistency, smell, taste, and about the properties of the object as a whole, i.e. a certain integral image of the perceived object is created. The interaction of analyzers in assessing phenomena and objects also underlies the compensation of impaired functions in the event of the loss of one of the analyzers. So, in the blind, the sensitivity of the auditory analyzer increases. Such people can determine the location of large objects and bypass them if there is no extraneous noise. This is done by reflecting sound waves from the object in front. American researchers observed a blind man who accurately determined the location of a large cardboard plate. When the subject's ears were covered with wax, he could no longer determine the location of the cardboard.

Interactions of sensory systems can manifest themselves in the form of the influence of excitation of one system on the state of excitability of another according to the dominant principle. For example, listening to music can cause pain relief during dental procedures (audio analgesia). Noise degrades visual perception, bright light increases the perception of sound volume. The process of interaction of sensory systems can manifest itself at various levels. A particularly important role in this is played by the reticular formation of the brain stem, the cerebral cortex. Many cortical neurons have the ability to respond to complex combinations of signals of different modalities (multisensory convergence), which is very important for learning about the environment and evaluating new stimuli.

Encoding information in analyzers

Concepts. Coding- the process of converting information into a conditional form (code), convenient for transmission over a communication channel. Any transformation of information in the departments of the analyzer is coding. In the auditory analyzer, the mechanical vibration of the membrane and other sound-conducting elements at the first stage is converted into a receptor potential, the latter ensures the release of the mediator into the synaptic cleft and the emergence of a generator potential, as a result of which a nerve impulse arises in the afferent fiber. The action potential reaches the next neuron, in the synapse of which the electrical signal is again converted into a chemical one, i.e., the code changes many times. It should be noted that at all levels of analyzers there is no restoration of the stimulus in its original form. This physiological coding differs from most technical communication systems, where the message, as a rule, is restored in its original form.

Codes of the nervous system. AT Computer technology uses a binary code, when two symbols are always used to form combinations - 0 and 1, which represent two states. Encoding of information in the body is carried out on the basis of non-binary codes, which makes it possible to obtain a greater number of combinations with the same code length. The universal code of the nervous system is the nerve impulses that propagate along the nerve fibers. At the same time, the content of information is determined not by the amplitude of the pulses (they obey the “All or Nothing” law), but by the frequency of the pulses (time intervals between individual pulses), their combination into bursts, the number of pulses in a burst, and the intervals between bursts. Signal transmission from one cell to another in all parts of the analyzer is carried out using a chemical code, i.e. various mediators. To store information in the CNS, coding is carried out using structural changes in neurons (mechanisms of memory).

Encoded characteristics of the stimulus. In analyzers, the qualitative characteristic of the stimulus (for example, light, sound), the strength of the stimulus, the time of its action, and also the space, i.e., are encoded. the place of action of the stimulus and its localization in the environment. All departments of the analyzer take part in coding all the characteristics of the stimulus.

In the peripheral section of the analyzer coding of the quality of the stimulus (type) is carried out due to the specificity of the receptors, i.e. the ability to perceive a stimulus of a certain type, to which it is adapted in the process of evolution, i.e. to the appropriate stimulus. Thus, a light beam excites only retinal receptors, other receptors (smell, taste, tactile, etc.) usually do not respond to it.

The strength of the stimulus can be encoded by a change in the frequency of impulses generated by receptors when the strength of the stimulus changes, which is determined by the total number of impulses per unit time. This is the so-called frequency coding. In this case, with an increase in the strength of the stimulus, the number of impulses arising in the receptors usually increases, and vice versa. When the strength of the stimulus changes, the number of excited receptors can also change, in addition, the coding of the strength of the stimulus can be carried out by different values ​​of the latent period and reaction time. A strong stimulus reduces the latent period, increases the number of impulses and lengthens the reaction time. The space is encoded by the size of the area on which the receptors are excited, this is spatial coding (for example, we can easily determine whether a pencil touches the skin surface with a sharp or blunt end). Some receptors are more easily excited when exposed to a stimulus at a certain angle (Pacini bodies, retinal receptors), which is an assessment of the direction of the stimulus to the receptor. The localization of the action of the stimulus is encoded by the fact that the receptors of various parts of the body send impulses to certain areas of the cerebral cortex.

The duration of the action of the stimulus on the receptor is encoded by the fact that it begins to be excited with the onset of the action of the stimulus and stops being excited immediately after the stimulus is turned off (temporal coding). It should be noted that the time of action of the stimulus in many receptors is not coded accurately enough due to their rapid adaptation and cessation of excitation with a constantly acting stimulus strength. This inaccuracy is partly compensated by the presence of on-, off-, and on-off receptors, which are excited, respectively, when the stimulus is turned on and off, and also when the stimulus is turned on and off. With a long-acting stimulus, when adaptation of the receptors occurs, a certain amount of information about the stimulus (its strength and duration) is lost, but sensitivity increases, i.e., receptor sensitization develops to a change in this stimulus. Strengthening the stimulus acts on the adapted receptor as a new stimulus, which is also reflected in a change in the frequency of impulses coming from the receptor.

In the conductive section of the analyzer, coding is carried out only at "switching stations", i.e., when a signal is transmitted from one neuron to another, where the code is changed. Information is not encoded in nerve fibers, they play the role of wires through which information is transmitted, encoded in receptors and processed in the centers of the nervous system.

There can be different intervals between impulses in a single nerve fiber, impulses are formed into bundles with a different number, and there can also be different intervals between individual bundles. All this reflects the nature of the information encoded in the receptors. In the nerve trunk, the number of excited nerve fibers can also change, which is determined by a change in the number of excited receptors or neurons at the previous signal transition from one neuron to another. At switching stations, for example, in the thalamus, information is encoded, firstly, due to a change in the volume of impulses at the input and output, and secondly, due to spatial coding, i.e. due to the connection of certain neurons with certain receptors. In both cases, the stronger the stimulus, the greater the number of neurons fired.

In the overlying parts of the CNS, a decrease in the frequency of neuronal discharges and the transformation of long-term impulses into short bursts of impulses are observed. There are neurons that are excited not only when a stimulus appears, but also when it is turned off, which is also associated with the activity of receptors and the interaction of the neurons themselves. Neurons, called "detectors", respond selectively to one or another parameter of the stimulus, for example, to a stimulus moving in space, or to a light or dark strip located in a certain part of the visual field. The number of such neurons, which only partially reflect the properties of the stimulus, increases at each subsequent level of the analyzer. But at the same time, at each subsequent level of the analyzer there are neurons that duplicate the properties of the neurons of the previous section, which creates the basis for the reliability of the function of the analyzers. In the sensory nuclei, inhibitory processes occur that filter and differentiate sensory information. These processes provide control of sensory information. This reduces the noise and changes the ratio of spontaneous and evoked activity of neurons. Such a mechanism is implemented due to the types of inhibition (lateral, recurrent) in the process of ascending and descending influences.

At the cortical end of the analyzer frequency-spatial coding occurs, the neurophysiological basis of which is the spatial distribution of ensembles of specialized neurons and their connections with certain types of receptors. Impulses arrive from receptors in certain areas of the cortex at different time intervals. Information coming in the form of nerve impulses is recoded into structural and biochemical changes in neurons (mechanisms of memory). In the cerebral cortex, the highest analysis and synthesis of the information received is carried out.

The analysis consists in the fact that with the help of the sensations that arise, we distinguish between the acting stimuli (qualitatively - light, sound, etc.) and determine the strength, time and place, i.e. the space on which the stimulus acts, as well as its localization (source of sound, light, smell).

Synthesis is realized in the recognition of a known object, phenomenon or in the formation of an image of an object, phenomenon encountered for the first time.

There are cases when blind from birth vision appeared only in adolescence. So, a girl who gained sight only at the age of 16 could not recognize objects with the help of sight, which she had repeatedly used before. But as soon as she took the object in her hands, she happily called it. She thus had to practically re-study the world around her with the participation of the visual analyzer, reinforced by information from other analyzers, in particular from the tactile one. At the same time, tactile sensations were decisive. This is evidenced, for example, by the long experience of Strato. It is known that the image on the retina is reduced and inverted. The newborn sees the world that way. However, in early ontogenesis, the child touches everything with his hands, compares and compares visual sensations with tactile ones. Gradually, the interaction of tactile and visual sensations leads to the perception of the location of objects as it is in reality, although the image remains upside down on the retina. Strato put on glasses with lenses that turned the image on the retina into a position corresponding to reality. The observed surrounding world turned upside down. However, within 8 days, by comparing tactile and visual sensations, he again began to perceive all things and objects as usual. When the experimenter took off his glasses, the world turned upside down again, normal perception returned after 4 days.

If information about an object or phenomenon enters the cortical section of the analyzer for the first time, then an image of a new object or phenomenon is formed due to the interaction of several analyzers. But even at the same time, the incoming information is compared with traces of memory about other similar objects or phenomena. The information received in the form of nerve impulses is encoded using the mechanisms of long-term memory.

So, the process of transmitting a sensory message is accompanied by multiple recoding and ends with a higher analysis and synthesis that occurs in the cortical section of the analyzers. After that, the choice or development of a program for the body's response already takes place.

sensory receptor visual analyzer

General plan of the structure of sensory systems

Name of analyzer	The nature of the stimulus	Peripheral department	conductor department	Central hotel
visual	Electromagnetic oscillations reflected or radiated by objects of the outside world and perceived by the organs of vision.	Rod and cone neurosensory cells, the outer segments of which are, respectively, rod-shaped (“rods”) and cone-shaped (“cones”) shapes. Rods are receptors that perceive light rays in low light conditions, i.e. colorless or achromatic vision. Cones, on the other hand, function in bright light conditions and are characterized by different sensitivity to the spectral properties of light (color or chromatic vision)	The first neuron of the conduction section of the visual analyzer is represented by bipolar cells of the retina. Axons of bipolar cells, in turn, converge to ganglion cells (the second neuron). Bipolar and ganglion cells interact with each other due to numerous lateral connections formed by collaterals of dendrites and axons of the cells themselves, as well as with the help of amacrine cells.	Located in the occipital lobe. There are complex and supercomplex receptive fields of the detector type. This feature allows you to select from the whole image only separate parts of lines with different locations and orientations, while the ability to selectively respond to these fragments is manifested.
auditory	Sounds, i.e., oscillatory movements of particles of elastic bodies propagating in the form of waves in a wide variety of media, including air, and perceived by the ear	Converting the energy of sound waves into the energy of nervous excitation, it is represented by receptor hair cells of the organ of Corti (the organ of Corti), located in the cochlea. The inner ear (sound-receiving apparatus), as well as the middle ear (sound-transmitting apparatus) and the outer ear (sound-catching apparatus) are combined into the concept hearing organ	It is represented by a peripheral bipolar neuron located in the spiral ganglion of the cochlea (the first neuron). The fibers of the auditory (or cochlear) nerve, formed by the axons of the neurons of the spiral ganglion, end on the cells of the nuclei of the cochlear complex of the medulla oblongata (the second neuron). Then, after a partial decussation, the fibers go to the medial geniculate body of the metathalamus, where the switch again occurs (the third neuron), from here the excitation enters the cortex (the fourth neuron). In the medial (internal) geniculate bodies, as well as in the lower tubercles of the quadrigemina, there are centers of reflex motor reactions that occur under the action of sound.	Located in the upper part of the temporal lobe of the brain. Important for the function of the auditory analyzer are the transverse temporal gyrus (Geshl's gyrus).
Vestibular	Provides the so-called acceleration feeling, i.e. a sensation that occurs with rectilinear and rotational acceleration of the movement of the body, as well as with changes in the position of the head. The vestibular analyzer plays a leading role in the spatial orientation of a person, maintaining his posture.	It is represented by hair cells of the vestibular organ, located, like the cochlea, in the labyrinth of the pyramid of the temporal bone. The vestibular organ (the organ of balance, the organ of gravity) consists of three semicircular canals and the vestibule. The vestibule consists of two sacs: round (sacculus), located closer to the cochlea, and oval (utriculus), located closer to the semicircular canals. For the hair cells of the vestibule, adequate stimuli are the acceleration or deceleration of the rectilinear movement of the body, as well as head tilts. For the hair cells of the semicircular canals, an adequate stimulus is the acceleration or deceleration of rotational movement in any plane.	Peripheral fibers of bipolar neurons of the vestibular ganglion located in the internal auditory canal (the first neuron) approach the receptors. The axons of these neurons as part of the vestibular nerve are sent to the vestibular nuclei of the medulla oblongata (the second neuron). The vestibular nuclei of the medulla oblongata (upper - Bechterew's nucleus, medial - Schwalbe's nucleus, lateral - Deiters' nucleus and lower - Roller's nucleus) receive additional information on afferent neurons from the proprioreceptors of the muscles or from the articular joints of the cervical spine. These nuclei of the vestibular analyzer are closely connected with various parts of the central nervous system. This ensures control and management of somatic, vegetative and sensory effector reactions. The third neuron is located in the nuclei of the thalamus, from where the excitation is sent to the cortex of the hemispheres.	The central department of the vestibular analyzer is localized in the temporal region of the cerebral cortex, somewhat anterior to the auditory projection zone (fields 21–22 according to Brodmann, the fourth neuron).
Motor	Provides the formation of the so-called muscle feeling when the tension of the muscles, their membranes, articular bags, ligaments, tendons changes. Three components can be distinguished in a muscular sense: a sense of position, when a person can determine the position of his limbs and their parts relative to each other; a sense of movement, when, by changing the angle of flexion in the joint, a person is aware of the speed and direction of movement; a sense of strength, when a person can assess the muscle strength needed to move or hold joints in a certain position when lifting or moving a load. Along with the skin, visual, vestibular motor analyzer evaluates the position of the body in space, posture, participates in the coordination of muscle activity	It is represented by proprioceptors located in muscles, ligaments, tendons, articular bags, fascia. These include muscle spindles, Golgi bodies, Pacini bodies, and free nerve endings. The muscle spindle is a collection of thin short striated muscle fibers that are surrounded by a connective tissue capsule. The muscle spindle with intrafusal fibers is located parallel to the extrafusal ones, therefore, they are excited during relaxation (lengthening) of the skeletal muscle. Golgi bodies are found in tendons. These are grape-shaped sensitive endings. The Golgi bodies, located in the tendons, are connected sequentially relative to the skeletal muscle, so they are excited when it contracts due to the tension of the muscle tendon. Golgi receptors control the force of muscle contraction, i.e. voltage. Panina's bodies are encapsulated nerve endings, localized in the deep layers of the skin, in tendons and ligaments, they respond to pressure changes that occur during muscle contraction and tension in tendons, ligaments and skin.	It is represented by neurons that are located in the spinal ganglia (the first neuron). The processes of these cells in the bundles of Gaulle and Burdach (posterior columns of the spinal cord) reach the delicate and sphenoid nuclei of the medulla oblongata, where the second neurons are located. From these neurons, the fibers of the muscular-articular sensitivity, having crossed, as part of the medial loop, reach the thalamus, where third neurons are located in the ventral posterolateral and posteromedial nuclei.	The central section of the motor analyzer is the neurons of the anterior central gyrus.
Internal (visceral)	They analyze and synthesize information about the state of the internal environment of the body and participate in the regulation of the work of internal organs. Can be distinguished: 1) an internal analyzer of pressure in blood vessels and pressure (fillings) in internal hollow organs (mechanoreceptors are the peripheral part of this analyzer); 2) temperature analyzer; 3) an analyzer of the chemistry of the internal environment of the organism; 4) analyzer of the osmotic pressure of the internal environment.	Mechanoreceptors include all receptors for which pressure is an adequate stimulus, as well as stretching, deformation of the walls of organs (vessels, heart, lungs, gastrointestinal tract and other internal hollow organs). Chemoreceptors include the entire mass of receptors that respond to various chemicals: these are the receptors of the aortic and carotid glomeruli, the receptors of the mucous membranes of the digestive tract and respiratory organs, the receptors of the serous membranes, and the chemoreceptors of the brain. Osmoreceptors are localized in the aortic and carotid sinuses, in other vessels of the arterial bed, in the interstitial tissue near the capillaries, in the liver and other organs. Some osmoreceptors are mechanoreceptors, some are chemoreceptors. Thermoreceptors are localized in the mucous membranes of the digestive tract, respiratory organs, Bladder, serous membranes, in the walls of arteries and veins, in the carotid sinus, as well as in the nuclei of the hypothalamus.	From interoreceptors, excitation mainly takes place in the same trunks with the fibers of the autonomic nervous system. The first neurons are located in the corresponding sensory ganglia, the second neurons are in the spinal or medulla oblongata. The ascending paths from them reach the posteromedial nucleus of the thalamus (the third neuron) and then rise to the cerebral cortex (the fourth neuron).	The cortical region is localized in zones C 1 and C 2 of the somatosensory cortex and in the orbital region of the cerebral cortex. The perception of some interoceptive stimuli may be accompanied by the appearance of clear, localized sensations, for example, when the walls of the bladder or rectum are stretched. But visceral impulses (from the interoreceptors of the heart, blood vessels, liver, kidneys, etc.) may not cause clearly conscious sensations. This is due to the fact that such sensations arise as a result of irritation of various receptors that are part of a particular organ system. In any case, changes in internal organs have a significant impact on the emotional state and behavior of a person.
Temperature	Provides information about the temperature of the external environment and the formation of temperature sensations	It is represented by two types of receptors: some respond to cold stimuli, others to heat. Heat receptors are Ruffini bodies, and cold receptors are Krause flasks. Cold receptors are located in the epidermis and directly below it, and heat receptors are located mainly in the lower and upper layers of the skin itself and the mucous membrane.	Myelinated type A fibers depart from cold receptors, and unmyelinated type C fibers depart from heat receptors, so information from cold receptors propagates at a faster rate than from thermal ones. The first neuron is localized in the spinal ganglia. The cells of the posterior horns of the spinal cord represent the second neuron. Nerve fibers extending from the second neurons of the temperature analyzer pass through the anterior commissure to the opposite side into the lateral columns and, as part of the lateral spinal-thalamic tract, reach the thalamic thalamus, where the third neuron is located. From here, excitation enters the cortex of the cerebral hemispheres.	The central section of the temperature analyzer is localized in the region of the posterior central gyrus of the cerebral cortex.
Tactile	Provides sensations of touch, pressure, vibration and tickling.	It is represented by various receptor formations, the irritation of which leads to the formation of specific sensations. On the surface of the skin devoid of hair, as well as on the mucous membranes, special receptor cells (Meissner bodies) located in the papillary layer of the skin react to touch. On the skin covered with hair, the hair follicle receptors, which have moderate adaptation, respond to touch.	From most mechanoreceptors in the spinal cord, information enters the central nervous system via A-fibers, and only from tickle receptors - via C-fibers. The first neuron is located in the spinal ganglia. In the posterior horn of the spinal cord, the first switch to interneurons (second neuron) occurs, from which the ascending path as part of the posterior column reaches the nuclei of the posterior column in the medulla oblongata (third neuron), where the second switch occurs, then through the medial loop the path follows to the ventrobasal nuclei of the thalamus opticus (fourth neuron), the central processes of the neurons of the thalamus go to the cerebral cortex.	It is localized in zones 1 and 2 of the somatosensory region of the cerebral cortex (posterior central gyrus).
Taste	The resulting sense of taste is associated with irritation of not only chemical, but also mechanical, temperature and even pain receptors of the oral mucosa, as well as olfactory receptors. The taste analyzer determines the formation of taste sensations, is a reflexogenic zone.	Taste receptors (taste cells with microvilli) are secondary receptors, they are an element of taste buds, which also include supporting and basal cells. Taste buds contain serotonin-containing cells and histamine-producing cells. These and other substances play a role in the formation of the sense of taste. Individual taste buds are polymodal formations, as they can perceive various types of taste stimuli. Taste buds in the form of separate inclusions are located on the back wall of the pharynx, soft palate, tonsils, larynx, epiglottis and are also part of the taste buds of the tongue as an organ of taste.	Inside the taste bud are nerve fibers that form receptor-afferent synapses. The taste buds of different areas of the oral cavity receive nerve fibers from different nerves: the taste buds of the anterior two-thirds of the tongue - from the drum string, which is part of facial nerve; kidneys of the posterior third of the tongue, as well as the soft and hard palate, tonsils - from the glossopharyngeal nerve; taste buds located in the pharynx, epiglottis and larynx - from the upper laryngeal nerve, which is part of the vagus nerve	It is localized in the lower part of the somatosensory zone of the cortex in the area of ​​representation of the language. Most of the neurons in this area are multimodal; reacts not only to taste, but also to temperature, mechanical and nociceptive stimuli. The taste sensory system is characterized by the fact that each taste bud has not only afferent, but also efferent nerve fibers that are suitable for taste cells from the central nervous system, which ensures the inclusion of the taste analyzer in the integral activity of the body.
Olfactory		Primary sensory receptors, which are the ends of the dendrite of the so-called neurosecretory cell. Top part the dendrite of each cell carries 6-12 cilia, and an axon departs from the base of the cell. Cilia, or olfactory hairs, are immersed in a liquid medium - a layer of mucus produced by Bowman's glands. The presence of olfactory hairs significantly increases the contact area of ​​the receptor with molecules of odorous substances. The movement of the hairs provides an active process of capturing the molecules of the odorous substance and contact with it, which underlies the targeted perception of odors. The receptor cells of the olfactory analyzer are immersed in the olfactory epithelium lining the nasal cavity, in which, in addition to them, there are supporting cells that perform a mechanical function and are actively involved in the metabolism of the olfactory epithelium. Part of the supporting cells located near the basement membrane is called basal	The first neuron of the olfactory analyzer should be considered a neurosensory or neuroreceptor cell. The axon of this cell forms synapses, called glomeruli, with the main dendrite of the mitral olfactory bulb cells, which represent the second neuron. The axons of the mitral cells of the olfactory bulbs form the olfactory tract, which has a triangular extension (olfactory triangle) and consists of several bundles. The fibers of the olfactory tract go in separate bundles to the anterior nuclei of the optic tubercle. Some researchers believe that the processes of the second neuron go directly to the cerebral cortex, bypassing the visual tubercles.	It is localized in the anterior part of the pear-shaped lobe of the cortex in the region of the sea horse gyrus.
	Pain is a "sensory modality" like hearing, taste, vision, etc., it performs a signaling function, which consists in information about the violation of such vital body constants as the integrity of the integumentary membranes and a certain level of oxidative processes in tissues that ensure their normal functioning. . At the same time, pain can be considered as a psychophysiological state, accompanied by changes in the activity of various organs and systems, as well as the emergence of emotions and motivations.	It is represented by pain receptors, which, at the suggestion of C. Sherrington, are called nociceptors. These are high-threshold receptors that respond to destructive influences. According to the mechanism of excitation, nociceptors are divided into mechanociceptors and chemociceptors. Mechanociceptors are located mainly in the skin, fascia, tendons, articular bags and mucous membranes of the digestive tract. Chemonociceptors are also located on the skin and in the mucous membranes, but prevail in the internal organs, where they are localized in the walls of small arteries.	Conduction of pain excitation from receptors is carried out along the dendrites of the first neuron, located in the sensory ganglia of the corresponding nerves that innervate certain parts of the body. The axons of these neurons enter the spinal cord to the intercalary neurons of the posterior horn (the second neuron). Further, the conduction of excitation in the central nervous system is carried out in two ways: specific (lemniscal) and nonspecific (extralemniscal). The specific path starts from the intercalary neurons of the spinal cord, the axons of which, as part of the spinothalamic tract, enter the specific nuclei of the thalamus (in particular, the ventrobasal nucleus), which represent the third neurons. The processes of these neurons reach the cortex. The nonspecific pathway also starts from the intercalary neuron of the spinal cord and goes through collaterals to various brain structures. Depending on the place of termination, three main tracts are distinguished - neospinothalamic, spinoreticular, spinomesencephalic. The last two tracts are combined into the spinothalamic. Excitation through these tracts enters the nonspecific nuclei of the thalamus and from there to all parts of the cerebral cortex.	The specific pathway ends in the somatosensory area of ​​the cerebral cortex. According to modern concepts, two somatosensory zones are distinguished. The primary projection zone is located in the region of the posterior central gyrus. Here there is an analysis of nociceptive influences, the formation of a sensation of acute, precisely localized pain. In addition, due to close connections with the motor cortex, motor acts are carried out when exposed to damaging stimuli. The secondary projection zone, which is located deep in the Sylvian sulcus, is involved in the processes of awareness and the development of a program of behavior in case of pain. The non-specific pathway extends to all areas of the cortex. A significant role in the formation of pain sensitivity is played by the orbitofrontal region of the cortex, which is involved in the organization of the emotional and autonomic components of pain.

Surrounding objects and phenomena do not always appear to us as
what they really are. We do not always see and hear what
what is actually happening.
P. Lindsay, D. Norman

One of the physiological functions of the body is the perception of the surrounding reality. Obtaining and processing information about the surrounding world is a necessary condition for maintaining the homeostatic constants of the organism and the formation of behavior. Among the stimuli acting on the body, only those for the perception of which there are specialized formations are caught and perceived. Such stimuli are called sensory stimuli, and complex structures designed to process them - sensory systems. Sensory signals differ in modality, i.e. the form of energy that is characteristic of each of them.

Objective and subjective side of perception

Under the action of a sensory stimulus, electrical potentials arise in the receptor cells, which are conducted to the central nervous system, where they are processed, which is based on the integrative activity of the neuron. An ordered sequence of physical and chemical processes occurring in the body under the action of a sensory stimulus represents the objective side of the functioning of sensory systems, which can be studied by the methods of physics, chemistry, and physiology.

The physicochemical processes developing in the central nervous system lead to the appearance of a subjective sensation. For example, electromagnetic vibrations with a wavelength of 400 nm cause the sensation "I see a blue color." The sensation is usually interpreted on the basis of prior experience, resulting in the perception "I see the sky." The emergence of sensation and perception reflects the subjective side of the work of sensory systems. The principles and patterns of the emergence of subjective sensations and perceptions are studied by the methods of psychology, psychophysics, and psychophysiology.

Perception is not a simple photographic display of the surroundings by sensory systems. A good illustration of this fact is two-valued pictures - the same image can be perceived in different ways (Fig. 1A). The objective side of perception is fundamentally similar in different people. The subjective side is always individual and is determined by the characteristics of the subject's personality, his experience, motivations, etc. Hardly any reader perceives the world around him in the same way as Pablo Picasso perceived it (Fig. 1B).

Specificity of sensory systems

Any sensory signal, regardless of its modality, is converted in the receptor into a specific sequence (pattern) of action potentials. The organism distinguishes between types of stimuli only due to the fact that sensory systems have the property of specificity, i.e. respond only to certain types of stimuli.

According to the law of “specific sensory energies” by Johannes Müller, the nature of the sensation is determined not by the stimulus, but by the irritated sensory organ. For example, with mechanical stimulation of the photoreceptors of the eye, there will be a sensation of light, but not pressure.

The specificity of sensory systems is not absolute, however, for each sensory system there is a certain type of stimulus (adequate stimuli), the sensitivity to which is many times higher than to other sensory stimuli (inadequate stimuli). The more the excitation thresholds of the sensory system differ for adequate and inadequate stimuli, the higher its specificity.

The adequacy of the stimulus is determined, firstly, by the properties of the receptor cells, and secondly, by the macrostructure of the sense organ. For example, the photoreceptor membrane is designed to perceive light signals, since it has a special protein called rhodopsin, which decomposes when exposed to light. On the other hand, the adequate stimulus for the receptors of the vestibular apparatus and the organ of hearing is the same - the endolymph flow, which deflects the cilia of the hair cells. However, the structure of the inner ear is such that the endolymph moves under the action of sound vibrations, and in the vestibular apparatus, the endolymph moves when the head position changes.

The structure of the sensory system

The sensor system includes the following elements (Fig. 2):
auxiliary apparatus
sensory receptor
sensory pathways
projection zone of the cerebral cortex.

The auxiliary apparatus is a formation whose function is the primary transformation of the energy of the current stimulus. For example, the auxiliary apparatus of the vestibular system converts angular accelerations body into mechanical displacement of hair cell kinocils. The auxiliary apparatus is not characteristic of all sensory systems.

The sensory receptor converts the energy of the acting stimulus into the specific energy of the nervous system, i.e. into an ordered sequence of nerve impulses. In the primary receptor, this transformation occurs at the endings of the sensitive neuron; in the secondary receptor, it occurs in the receptor cell. The axon of a sensory neuron (primary afferent) conducts nerve impulses to the CNS.

In the central nervous system, excitation is transmitted along a chain of neurons (the so-called sensory pathway) to the cerebral cortex. The axon of a sensitive (sensory) neuron forms synaptic contacts with several secondary sensory neurons. The axons of the latter follow to the neurons located in the nuclei of higher levels. Along the sensory pathways, information is processed, which is based on the integrative activity of the neuron. The final processing of sensory information occurs in the cerebral cortex.

Principles of organization of sensory pathways

The principle of multi-channel information. Each neuron of the sensory pathway forms contacts with several neurons of higher levels (divergence). Therefore, nerve impulses from one receptor are conducted to the cortex through several chains of neurons (parallel channels) (Fig. 3). Parallel multichannel transmission of information provides high reliability of sensory systems even in the conditions of loss of individual neurons (as a result of a disease or injury), as well as a high speed of information processing in the CNS.

The principle of duality of projections. Nerve impulses from each sensory system are transmitted to the cortex along two fundamentally different pathways - specific (monomodal) and nonspecific (multimodal).

Specific pathways conduct nerve impulses from the receptors of only one sensory system, because neurons of only one sensory modality converge on each neuron of such a pathway (monomodal convergence). Accordingly, each sensory system has its own specific pathway. All specific sensory pathways pass through the nuclei of the thalamus and form local projections in the cerebral cortex, ending in the primary projection zones of the cortex. Specific sensory pathways provide the initial processing of sensory information and conduct it to the cerebral cortex.

Neurons of different sensory modalities converge on neurons of the nonspecific pathway (multimodal convergence). Therefore, in the non-specific sensory pathway, information from all sensory systems of the body is integrated. The non-specific pathway of information transmission passes through the reticular formation and forms extensive diffuse projections in the projection and associative zones of the cortex.

Nonspecific pathways provide multibiological processing of sensory information and maintain an optimal level of excitation in the cerebral cortex.

The principle of somatotopic organization characterizes only specific sensory pathways. According to this principle, excitation from neighboring receptors enters adjacent areas of the subcortical nuclei and cortex. Those. the perceiving surface of any sensitive organ (the retina of the eye, the skin) is, as it were, projected onto the cerebral cortex.

The principle of top-down control. Excitation in sensory pathways is carried out in one direction - from receptors in the cerebral cortex. However, the neurons that make up the sensory pathways are under the downward control of the overlying parts of the CNS. Such connections make it possible, in particular, to block the transmission of signals in sensory systems. It is assumed that this mechanism may underlie the phenomenon of selective attention.

The main characteristics of sensations

The subjective sensation resulting from the action of a sensory stimulus has a number of characteristics, i.e. allows you to determine a number of parameters of the acting stimulus:
quality (modality),
intensity,
temporal characteristics (the moment of the beginning and end of the action of the stimulus, the dynamics of the strength of the stimulus),
spatial localization.

Quality coding stimulus in the CNS is based on the principle of specificity of sensory systems and the principle of somatotopic projection. Any sequence of nerve impulses that have arisen in the pathways and cortical projection zones of the visual sensory system will cause visual sensations.

Intensity coding - see the section of the course of lectures "Elementary physiological processes", lecture 5.

Timing coding cannot be separated from intensity coding. When the strength of the acting stimulus changes over time, the frequency of action potentials generated in the receptor will also change. With prolonged action of a stimulus of constant strength, the frequency of action potentials gradually decreases (for more details, see the section of the course of lectures "Elementary physiological processes", lecture 5.), Therefore, the generation of nerve impulses may stop even before the stimulus stops.

Spatial localization coding. The body can accurately determine the localization of many stimuli in space. The mechanism for determining the spatial localization of stimuli is based on the principle of somatotopic organization of sensory pathways.

The dependence of the intensity of sensation on the strength of the stimulus (psychophysics)

An absolute threshold is the smallest stimulus that can evoke a particular sensation. The value of the absolute threshold depends on
characteristics of the current stimulus (for example, the absolute threshold for sounds of different frequencies will be different);
the conditions under which the measurement is carried out;
functional state of the body: focus of attention, degree of fatigue, etc.

Differential threshold - the minimum amount by which one stimulus must differ from another in order for this difference to be felt by a person.

Weber's Law

In 1834, Weber showed that in order to distinguish the weight of 2 objects, their difference should be greater if both objects are heavy and less if both objects are light. According to Weber's law, differential threshold value ( Dj) is directly proportional to the strength of the acting stimulus ( j) .

where Dj - the minimum increase in stimulus strength required to cause an increase in sensation (differential threshold) , j - the strength of the current stimulus.

Graphically, this pattern is shown in Fig. 4A. Weber's law is valid for medium and high stimulus intensities; at low stimulus intensities, it is necessary to introduce a correction constant into the formula a.

Rice. 4. Graphic representation of Weber's law (A) and Fechner's law (B).

Fechner's law

Fechner's law establishes a quantitative relationship between the strength of the current stimulus and the intensity of sensation. According to Fechner's law, the strength of sensation is proportional to the logarithm of the strength of the acting stimulus.

where Y is the intensity of sensation, k- coefficient of proportionality, j- the strength of the current stimulus, j 0 - stimulus strength corresponding to the absolute threshold

Fechner's law was derived from Weber's law. The unit of intensity of sensation was taken as "barely perceptible sensation". Under the action of a stimulus, the magnitude of which is equal to the absolute threshold of sensation, there is a minimum sensation. In order to feel a barely perceptible increase in sensation, the strength of the stimulus must be increased by some amount. In order to feel a further barely noticeable increase in sensation, the increase in stimulus strength must be large (according to Weber's law). With a graphical representation of this process, a logarithmic curve is obtained (Fig. 4B).

Stevens law

Fechner's law is based on the assumption that the strength of the sensation caused by the threshold increase of a weak and strong stimulus is equal, which is not entirely true. Therefore, the dependence of the intensity of sensation on the strength of the stimulus is more correctly described by the formula proposed by Stevens. The Stevens formula was proposed on the basis of experiments in which the subject was asked to subjectively evaluate in points the intensity of sensation caused by stimuli of various strengths. According to Stevens' law, the intensity of sensation is described by an exponential function.

,

where a- an empirical exponent, which can be either greater or less than 1, the rest of the designations are the same as in the previous formula.