Sense organs. Sensory systems. Abstract: Human sensory systems

The sensory organization of a personality is the level of development of individual sensitivity systems and the possibility of their unification. Human sensory systems are his sense organs, like receivers of his sensations, in which the transformation of sensation into perception occurs.

The main feature of a person’s sensory organization is that it develops as a result of his entire life path. A person’s sensitivity is given to him at birth, but its development depends on the circumstances, desires and efforts of the person himself. Feeling – lower mental process of reflecting individual properties of objects or phenomena of the internal and external world through direct contact.

It is obvious that the primary cognitive process occurs in the human sensory systems and, on its basis, cognitive processes that are more complex in structure arise: perceptions, ideas, memory, thinking. No matter how simple the primary cognitive process may be, it is precisely it that is the basis of mental activity; only through the “inputs” of sensory systems does the surrounding world penetrate into our consciousness. The physiological mechanism of sensations is the activity of the nervous apparatus - analyzers, consisting of 3 parts:

· receptor- the perceiving part of the analyzer (carries out the transformation of external energy into a nervous process)

· central section of the analyzer- afferent or sensory nerves

· cortical sections of the analyzer, in which nerve impulses are processed.

Each type of sensation is characterized not only by specificity, but also has common properties with other types: quality, intensity, duration, spatial localization. The minimum magnitude of the stimulus at which the sensation appears is absolute threshold of sensation. The value of this threshold characterizes absolute sensitivity, which is numerically equal to a value inversely proportional to the absolute threshold of sensations. Sensitivity to changes in stimulus is called relative or difference sensitivity. The minimum difference between two stimuli that causes a slightly noticeable difference in sensation is called difference threshold.

Classification of sensations

A widespread classification is based on the modality of sensations (specificity of the sense organs) - this is the division of sensations into visual, auditory, vestibular, tactile, olfactory, gustatory, motor, visceral. There are intermodal sensations - synesthesia. The main and most significant group of sensations brings information from the outside world to a person and connects him with the external environment. These are exteroceptive - contact and distant sensations; they occur in the presence or absence of direct contact of the receptor with the stimulus. Vision, hearing, and smell are distant sensations. These types of sensations provide orientation in the immediate environment. Taste, pain, tactile sensations are contact. According to the location of the receptors on the surface of the body, in muscles and tendons or inside the body, they are distinguished accordingly:

– exteroceptive sensations (arising from the influence of external stimuli on receptors located on the surface of the body, externally) visual, auditory, tactile;

– proprioceptive(kinesthetic) sensations (reflecting the movement and relative position of body parts with the help of receptors located in muscles, tendons, joint capsules);

– interoceptive(organic) sensations - arising from the reflection of metabolic processes in the body with the help of specialized receptors, hunger and thirst.

In order for a sensation to arise, it is necessary that the stimulus reaches a certain value, which is called threshold of perception.
Relative threshold- the magnitude that the stimulus must reach for us to feel this change.
Absolute thresholds– these are the upper and lower limits of the organ’s resolution. Threshold research methods:

Bounds method

consists in gradually increasing the stimulus from subthreshold, then the reverse procedure

Installation method

the subject independently distinguishes the magnitude of the stimulus

Sensory systems are considered components of the nervous system, which is involved in the perception of information from the outside world, its transmission into the brain and analysis. Receiving data from the environment and one’s body is a necessary factor for an individual’s life.

This analyzer is one of the most important components of the central nervous system, which involves sensory receptors, nerve fibers that carry information to the brain and its parts. Next, they begin to process and analyze the data.

General information

Each analyzer implies the presence of peripheral receptors, conducting ducts and switching nuclei. In addition, they have a special hierarchy and have several levels of step-by-step data processing. At the lowest level of such perception, primary sensory neurons located in special sensory organs or ganglia are involved. They help conduct excitation from peripheral receptors to the central nervous system. Peripheral receptors are receptive, highly specialized neoplasms that are capable of perceiving, converting and transmitting external energy to primary sensory neurons.

Device principle

To understand how the sensory system functions, you need to learn about its structure. There are 3 components:

• peripheral (receptors);
• conductive (methods of excitation);
• central (cortical neurons that analyze the stimulus).

The beginning of the analyzer is receptors, and the end is neurons. Analyzers should not be confused with . The former lack the effector part.

How sensor systems work

General rules for the operation of analyzers:

• Conversion of irritation into a frequency code of pulse signals. Is the universal functioning of any receptor. In each of them, treatment will begin with changes in the characteristics of the cell membrane. Under the influence of a stimulus, controlled ion channels open inside the membrane. They spread through these channels and depolarization occurs.
• Topic matching. The flow of information in the transmission structure must correspond to the essential indicators of the stimulus. This may mean that its key indicators will be encoded as a stream of impulses and the NS will create an image that will be similar to the stimulus.
• Detection. Is a department of qualitative symptoms. Neurons begin to react to specific manifestations of the object and not perceive others. They are characterized by sharp transitions. Detectors add meaning and identity to a fuzzy pulse. In different pulses they highlight similar parameters.
• Distortion of information about the analyzed object at all levels of excitation.
• Specificity of receptors. Their susceptibility is maximum to a specific type of stimulus with varying strengths.
• Inverse relationship between structures. Subsequent structures are capable of changing the state of the previous ones and the characteristics of the flow of excitation entering them.

Visual system

Vision is a multi-element process that begins with the projection of an image onto the retina. After the photoreceptors are excited, they are then transformed in the neural layer and finally a decision is made about the sensory image.

The visual analyzer involves certain departments:

• Peripheral. An additional organ is the eye, where receptors and neurons are concentrated.
• Conductor. The optic nerve, which represents the fibers of 2 neurons and transmits data to 3. Some of them are located in the midbrain, the second - in the intermediate brain.
• Cortical. 4 neurons are concentrated in the cerebral hemispheres. This formation is the primary field or core of the sensory system, the purpose of which will be the formation of sensations. Near it there is a secondary field, the purpose of which is to recognize and process the sensory image, which will become the foundation of perception. Subsequent transformation and connection of data with information from other analyzers is observed in the lower parietal region.

Auditory system

The auditory analyzer provides encoding of acoustic images and makes it possible to orient in space thanks to the assessment of the stimulus. The peripheral areas of this analyzer represent the hearing organs and phonoreceptors located in the inner ear. Based on the formation of analyzers, the nominative purpose of speech appears - the association of things and names.

The auditory analyzer is considered one of the most important because it becomes a means of communication between people.

Outer ear

The external passage of the ear helps conduct sound impulses into the eardrum, which separates the outer ear from the middle ear. It is a thin partition and looks like a funnel oriented inward. After exposure to sound impulses through the outer ear, the membrane vibrates.

Middle ear

It contains 3 bones: the malleus, the incus and the stirrup, which gradually transform the vibrational impulses of the eardrum into the inner ear. The handle of the malleus is woven into the membrane itself, and part 2 is connected to the anvil, which in turn directs the impulse of the stapes. It transmits impulses of smaller amplitude, but more intense. There are 2 muscles located inside the middle ear. The stirrup secures the stirrup, preventing it from moving, and the tensioner contracts and increases tension. By contracting after approximately 10 ms, these muscles prevent overload in the inner ear.

Structure of the snail

The inner ear contains the cochlea, which is a bony spiral with dimensions of 0.04 mm in width and 0.5 mm at the top. This channel is divided by 2 membranes. At the top of the cochlea, each of these membranes is connected. The upper one will overlap with the lower canal through the foramen ovale using the scala tympani. They are filled with perilymph, similar in consistency to cerebrospinal fluid. In the middle of the 2 channels there is a membranous one, which is filled with endolymph. In it, on the main membrane, there is an apparatus that perceives sounds and includes receptor cells that convert mechanical impulses.

Olfactory

This analyzer perceives and analyzes chemical stimuli that are located in the surrounding world and act on the olfactory system. The process itself is the perception through special organs of any characteristics (flavors) of various substances.

The olfactory system in an individual is expressed by the epithelium, which is located at the top of the nasal cavity and includes sections of the lateral concha and septum on each side. It is enveloped in olfactory mucus and includes special chemoreceptors, supporting and basal cells. The respiratory area has free endings of sensory fibers that react to aromatic substances.

Contains the following departments:

• Peripheral. Involves olfactory organs and epithelium, which contain chemoreceptors and nerve fibers. There are no common elements in the paired conductive ducts, so damage to the centers of smell on one side is likely.
• Secondary data conversion center. Assumes the presence of primary centers of smell and an auxiliary organ.
• Central. The final authority for data processing, which is located in the forebrain.

Somatosensory

The somatosensory analyzer involves the neural processes that process sensory data throughout the body. Somatic perception is opposed to specific sensations that involve visual and auditory function, aroma, taste and coordination.

There are 3 physiological types of such sensations:

• mechanoreceptive, which include touch and orientation (stimulated by mechanical movements of certain tissues in the body);
• thermoreceptive, manifested under the influence of temperature indicators;
• painful, formed under the influence of any factors that damage tissue.

There are other criteria for dividing such sensations:

• exteroceptive, which appear in the process of irritation of a receptor located on the body;
• proprioceptive, which relate to physical condition (body position, muscle and tendon tone, level of pressure on the feet and sense of coordination).

Visceral sensations are associated with the state of the body. Deep feelings come from deep tissues. These include mainly “deep” pressure, pain and vibration.

The Essence of Perception

It is a more confusing psycho-emotional process regarding sensation. Perception is a holistic image of objects and events that arise as a result of the synthesis of sensations. During this process, the identification of the most significant and important characteristics of an object is noted, with separation from those that are insignificant for such a case, and the correlation of what is perceived with the experience experienced. Any perception presupposes an active functional component (palpation, eye activity when examining, etc.) and complex analytical work of the brain.

Perception can manifest itself in the following forms: conscious, subliminal and extrasensory.

Specialists mainly study the study of the conscious, having made great progress in understanding the mechanisms and patterns of this process. Its study is based on data from psychophysiological studies.

The sensory system is a complex of peripheral and central parts of the central nervous system, which are responsible for receiving impulses of various images from the outside world or one’s own body.

This structure suggests the presence of receptors, neural ducts and sections in the brain. They are responsible for converting outgoing signals. The most famous are the visual, auditory, olfactory, and somatosensory analyzers. Thanks to them, it is possible to differentiate various physical characteristics (temperature, taste, sound vibrations or pressure). Sensory analyzers are the most important elements of the individual’s nervous system. They take an active part in processing data from the external environment, its transformation and analysis. Reception of information from the environment will become a necessary condition for life.

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• Introduction
• Conclusion
• Applications
• Introduction
• One of the physiological functions of the body is the perception of the surrounding reality. Receiving and processing information about the surrounding world is a necessary condition for maintaining the homeostatic constants of the body and shaping behavior. Among the stimuli acting on the body, only those for which there are specialized formations are captured and perceived. Such stimuli are called sensory stimuli, and complex structures designed to process them are called sensory systems (sense organs).
• The human sensory system consists of the following subsystems: visual system, auditory system, somatosensory system, gustatory system, olfactory system.

The sensory information that we receive with the help of our sense organs (analyzers) is important not only for organizing the activities of internal organs and behavior in accordance with the requirements of the environment, but also for the full development of a person.

Sense organs are “windows” through which the outside world enters our consciousness. Without this information, the optimal organization of both the most primitive, “animal” functions of our body, and the higher cognitive mental processes of a person would be impossible.

However, a person does not perceive all changes in the environment; he is not able, for example, to sense the effects of ultrasound, X-rays or radio waves. The range of human sensory perception is limited by the sensory systems available to him, each of which processes information about stimuli of a certain physical nature.

• The purpose and objectives of this work are to consider the concept of “sensory systems”, analyze human sensory systems and determine the significance of each of them in human development and life.
• 1. Psychophysiology of sensory systems: concept, functions, principles, general properties
• sensory analyzer brain man
• Human sensory systems are part of his nervous system, capable of perceiving information external to the brain, transmitting it to the brain and analyzing it. Receiving information from the environment and one's own body is a prerequisite for human existence.
• The sensory system (Latin sensus - feeling) is a set of peripheral and central structures of the nervous system, which consists of a group of cells (receptors) responsible for perceiving signals of various modalities from the environment or internal environment, transmitting it to the brain and analyzing it. Smirnov V.M. Physiology of sensory systems and higher nervous activity: Proc. allowance / V.M. Smirnov, S.M. Budylina. - M.: Academy, 2009. - 304 p. - pp. 178-196.
• The term “sensory systems” replaced the name “sense organs,” which was retained only to designate the anatomically separate peripheral parts of certain sensory systems (such as the eye or ear). In the domestic literature, the concept of “analyzer”, proposed by I.P., is used as a synonym for the sensory system. Pavlov and indicating the function of the sensory system.

The human sensory system consists of the following subsystems: visual system, auditory system, somatosensory system, gustatory system, olfactory system. Types of analyzers are shown in Appendix 1.

• According to I.P. Pavlov, any analyzer has three main sections (Table 1):
• 1. The peripheral part 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. The perception of stimuli in the receptors occurs through the transformation of the energy of the stimulus into a nerve impulse (this part represents the sense organs - the eye, ear, etc.).
• 2. The conductor section of the analyzer includes afferent (peripheral) and intermediate neurons of the stem and subcortical structures of the central nervous system (CNS). It ensures the conduction of excitation from receptors to the cerebral cortex. In the conduction department, partial processing of information occurs at switching stages (for example, in the thalamus).

3. The central, or cortical section of the analyzer, consists of two parts: the central part - the “core” - represented by specific neurons that process afferent information from receptors, and the peripheral part - “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. These structural features of the central department ensure the process of compensation for impaired functions. At the level of the cortical region, higher analysis and synthesis of afferent excitations are carried out, which provide a complete picture of the environment.

• Table 1 - Comparative characteristics of the departments of the sensory system
• Comparative characteristics of the peripheral sections of the analyzers, and comparative characteristics of the conductive and central sections of the analyzers are presented in Appendix 2.
• Sensory systems are organized hierarchically, i.e. include several levels of sequential information processing. The lowest level of such processing is provided by primary sensory neurons, which are located in specialized sensory organs or in sensory ganglia and are designed to carry excitation from peripheral receptors to the central nervous system.
• Peripheral receptors are sensitive, highly specialized formations that are capable of perceiving, transforming and transmitting the energy of an external stimulus to primary sensory neurons. The central processes of primary sensory neurons end in the brain or spinal cord on second-order neurons, the bodies of which are located in the switching nucleus. It contains not only excitatory, but also inhibitory neurons involved in processing transmitted information.
• Representing a higher hierarchical level, neurons of the switching nucleus can regulate the transmission of information by enhancing some and inhibiting or suppressing other signals. Axons of second-order neurons form pathways to the next switching nucleus, the total number of which is determined by the specific features of different sensory systems. The final processing of information about the current stimulus occurs in the sensory areas of the cortex.

Each sensory system forms connections with various structures of the motor and integrative systems of the brain. Sensory systems are a necessary link for the formation of responses to environmental influences. The sensory system is characterized by the presence of feedback addressed to the receptor or first central section. Activating them makes it possible to regulate the process of perceiving information and its conduction along ascending pathways in the brain.

• Each individual sensory system reacts only to certain physical stimuli (for example, the visual system responds to light stimuli, the auditory system to sound stimuli, etc.). The specificity of such a reaction determined the concept of “modality”. A stimulus of a given modality, adequate for a particular sensory system, is considered to be a stimulus that evokes a reaction with minimal physical intensity. According to modality, stimuli are divided into mechanical, chemical, thermal, light, etc.
• All sensory systems, regardless of the nature of the current stimulus, perform the same functions and have common principles of their structural organization. At the same time, the most important principles are as follows: Batuev A.S. Physiology of higher nervous activity and sensory systems. General principles of design of sensor systems / A.S. Batuev. - St. Petersburg: Peter, 2010. - pp. 46-51. - 317 p.

1. The principle of multi-channel (duplication in order to increase the reliability of the system).

2. The principle of multi-level information transfer.

3. The principle of convergence (the terminal branches of one neuron contact several neurons of the previous level; Sherrington’s funnel).

4. The principle of divergence (animation; contact with several neurons of a higher level).

5. The principle of feedback (all levels of the system have both an ascending and descending path; feedback has an inhibitory value as part of the signal processing process).

6. The principle of corticalization (all sensory systems are represented in the new cortex; therefore, the cortex is functionally multivalued, and there is no absolute localization).

7. The principle of bilateral symmetry (exists to a relative extent).

8. The principle of structural-functional correlations (corticalization of different sensory systems has different degrees).

Basic functions of sensory systems: Bezrukikh M.M. Psychophysiology. Dictionary / M.M. Bezrukikh, D.A. Faber - M.: PER SE, 2006. - signal detection; signal discrimination; transmission and transformation; coding and detection of features; pattern recognition. This sequence is observed in all sensory systems, reflecting the hierarchical principle of their organization. At the same time, detection and primary discrimination of signals is provided by receptors, and detection and identification of signals by neurons of the cerebral cortex. Transmission, transformation and coding of signals is carried out by neurons of all layers of sensory systems.

1. Detection of signals begins in a receptor - a specialized cell, evolutionarily adapted to perceive a stimulus of a certain modality from the external or internal environment and convert it from a physical or chemical form into a form of nervous excitation.

2. An important characteristic of the sensory system is the ability to notice differences in the properties of simultaneously or sequentially acting stimuli. Discrimination begins in the receptors, but this process involves neurons throughout the sensory system. It characterizes the minimum difference between stimuli that the sensory system can notice (differential, or difference, threshold).

3. The processes of transformation and transmission of signals in the sensory system convey to the higher centers of the brain the most important (essential) information about the stimulus in a form convenient for its reliable and quick analysis. Signal transformations can be conditionally divided into spatial and temporal. Among spatial transformations, changes in the ratio of different parts of the signal are distinguished.

4. Information coding is the transformation of information into a conditional form - a code - carried out according to certain rules. In a sensory system, signals are encoded with a binary code, i.e., the presence or absence of an electrical impulse at a given time. Information about stimulation and its parameters is transmitted in the form of individual impulses, as well as groups or “packs” of impulses (“volleys” of impulses). The amplitude, duration and shape of each pulse are the same, but the number of pulses in a burst, their repetition rate, the duration of the bursts and the intervals between them, as well as the temporal “pattern” of the burst are different and depend on the characteristics of the stimulus. Sensory information is also encoded by the number of simultaneously excited neurons, as well as the location of excitation in the neural layer.

5. Signal detection is the selective selection by a sensory neuron of one or another sign of a stimulus that has behavioral significance. This analysis is carried out by detector neurons that selectively respond only to certain stimulus parameters. Thus, a typical neuron in the visual cortex responds with a discharge to only one specific orientation of a dark or light strip located in a certain part of the visual field. At other inclinations of the same strip, other neurons will respond. Detectors of complex features and entire images are concentrated in the higher parts of the sensory system.

6. Pattern recognition is the final and most complex operation of the sensory system. It consists in assigning an image to one or another class of objects that the organism has previously encountered, i.e., in the classification of images. By synthesizing signals from detector neurons, the higher department of the sensory system forms an “image” of the stimulus and compares it with many images stored in memory. Identification ends with a decision about what object or situation the organism encountered. As a result of this, perception occurs, i.e. we realize whose face we see in front of us, whom we hear, what smell we smell. Recognition often occurs regardless of signal variability. Thus, we reliably identify objects under different illumination, color, size, angle, orientation and position in the field of view. This means that the sensory system forms an (invariant) sensory image independent of changes in a number of signal features.

Thus, the sensory system (analyzer) is a functional system consisting of a receptor, an afferent pathway and a zone of the cerebral cortex where this type of sensitivity is projected.

The cortical analyzers of the human brain and their functional connections with various organs are clearly shown in the figure in Appendix 3.

Human sensory systems provide:

1) formation of sensations and perception of current stimuli;

2) control of voluntary movements;

3) control of the activities of internal organs;

4) the level of brain activity necessary for a person to be awake.

The process of transmitting sensory signals (they are often called sensory messages) is accompanied by their multiple transformations and recoding at all levels of the sensory system and ends with the recognition of a sensory image. Sensory information entering the brain is used to organize simple and complex reflex acts, as well as to form mental activity. The entry of sensory information into the brain may be accompanied by awareness of the presence of a stimulus (sensation of the stimulus). Sensation is a subjective sensory response to an actual sensory stimulus (for example, the sensation of light, heat or cold, touch, etc.). as mentioned earlier, the totality of sensations provided by any one analyzer is denoted by the term “modality,” which can include various qualitative types of sensations. Independent modalities are touch, vision, hearing, smell, taste, feeling of cold or heat, pain, vibration, sensation of limb position and muscle load. Within modalities there are different qualities, or submodalities; For example, the taste modality distinguishes between sweet, salty, sour and bitter tastes.

Based on the totality of sensations, sensory perception is formed, i.e., comprehension of sensations and readiness to describe them. Perception is not a simple reflection of the current stimulus; it depends on the distribution of attention at the moment of its action, the memory of past sensory experience and the subjective attitude to what is happening, expressed in emotional experiences.

Thus, the sensory system enters information into the brain and analyzes it. The work of any sensory system begins with the perception by receptors of physical or chemical energy external to the brain, transforming it into nerve signals and transmitting them to the brain through chains of neurons. The process of transmitting sensory signals is accompanied by their repeated transformation and recoding and ends with higher analysis and synthesis (image recognition), after which the body’s response is formed.

2. Characteristics of the main sensory systems

In physiology, it is customary to divide analyzers into external and internal. External human analyzers react to those stimuli that come from the external environment. Human internal analyzers are those structures that respond to changes within the body. For example, muscle tissue has specific receptors that respond to pressure and other indicators that change inside the body.

External analyzers are divided into contact (in direct contact with the stimulus) and distant, which respond to remote stimuli:

1) contact: taste and touch;

2) distant: vision, hearing and smell.

The activity of each of the sense organs represents an elementary mental process - sensation. Sensory information from external stimuli enters the central nervous system in 2 ways:

1) Characteristic sensory pathways:

a) vision - through the retina, lateral geniculate body and superior colliculus into the primary and secondary visual cortex;

b) hearing - through the nuclei of the cochlea and quadrigeminal, the medial geniculate body into the primary auditory cortex;

c) taste - through the medulla oblongata and thalamus to the somatosensory cortex;

d) smell - through the olfactory bulb and piriform cortex to the hypothalamus and limbic system;

e) touch - passes through the spinal cord, brain stem and thalamus to the somatosensory cortex.

2) Nonspecific sensory pathways: pain and temperature sensations located in the nuclei of the thalamus and brain stem.

The visual sensory system provides the brain with more than 90% of sensory information. Vision is a multi-link process that begins with the projection of an image onto the retina. Then the photoreceptors are excited, the transmission and transformation of visual information occurs in the neural layers of the visual system, and visual perception ends with the decision about the visual image being made by the higher cortical parts of this system.

The adaptation of the eye to clearly seeing objects at different distances is called accommodation; the main role here is played by the lens, which changes its curvature and, consequently, refractive power.

The peripheral part of the visual sensory system is the eye (Fig. 1). It consists of the eyeball and supporting structures: lacrimal glands, ciliary muscle, blood vessels and nerves. Characteristics of the membranes of the eyeball in Appendix 4.

The conductive section of the visual sensory system is the optic nerve, the nuclei of the superior colliculus of the midbrain, and the nuclei of the external geniculate body of the diencephalon.

The central section of the visual analyzer is located in the occipital lobe.

The eyeball has a spherical shape, which makes it easier to rotate to point at the object in question. The amount of light that enters the retina is regulated by the pupil, which is capable of dilating and contracting. The pupil is the hole in the center of the iris through which light rays pass into the eye. The pupil sharpens the image on the retina, increasing the depth of field of the eye.

The light beam breaks on the cornea, lens and vitreous body. Thus, the image falls on the retina, which contains many nerve receptors - rods and cones. Thanks to chemical reactions, an electrical impulse is formed here, which follows the optic nerve and is projected in the occipital lobes of the cerebral cortex.

Figure 1 - Organ of vision:

1 - tunica albuginea; 2 - cornea; 3 - lens; 4 - ciliary body; 5 - iris; 6 - choroid; 7 - retina; 8 - blind spot; 9 - vitreous body; 10 - posterior chamber of the eye; 11 - anterior chamber of the eye; 12 - optic nerve

The retina is the inner light-sensitive layer of the eye. There are two types of photoreceptors here (rods and cones: cones function in high light conditions, they provide daytime and color vision; much more photosensitive rods are responsible for twilight vision) and several types of nerve cells. All of the listed retinal neurons with their processes form the nervous apparatus of the eye, which not only transmits information to the visual centers of the brain, but also participates in its analysis and processing. Therefore, the retina is called the part of the brain located in the periphery. From the retina, visual information travels along the optic nerve fibers to the brain.

The auditory sensory system is one of the most important distant sensory systems in humans. The receptor here is the ear. Like any other analyzer, the auditory one also consists of three parts: the auditory receptor, the auditory nerve with its pathways and the auditory zone of the cerebral cortex, where the analysis and assessment of sound stimulation occurs (Fig. 2).

The peripheral auditory sensory system consists of three parts: the outer, middle and inner ear.

Wiring department. The hair cells are covered by the nerve fibers of the cochlear branch of the auditory nerve, which carries the nerve impulse to the medulla oblongata, then, crossing with the second neuron of the auditory tract, it is directed to the posterior colliculus and the nuclei of the internal geniculate bodies of the diencephalon, and from them to the temporal region of the cortex, where the central part of the auditory analyzer is located.

Figure 2 - Hearing organ:

A - general view: 1 - external auditory canal; 2 - eardrum; 3 - middle ear;

4 - hammer; 5 - anvil; 6 - stirrup; 7 - auditory nerve; 8 - snail; 9 - auditory (Eustachian) tube; B - section of the cochlea; B - cross section of the cochlear canal: 10 - bone labyrinth; 11 - membranous labyrinth; 12 - spiral (Corti) organ; 13 - main (basal) plate

The central section of the auditory analyzer is located in the temporal lobe. The primary auditory cortex occupies the upper edge of the superior temporal gyrus and is surrounded by the secondary cortex. The meaning of what is heard is interpreted in associative zones. In humans, in the central nucleus of the auditory analyzer, Wernicke's area, located in the posterior part of the superior temporal gyrus, is of particular importance. This zone is responsible for understanding the meaning of words; it is the center of sensory speech. With prolonged exposure to strong sounds, the excitability of the sound analyzer decreases, and with prolonged exposure to silence it increases. This adaptation is observed in the zone of higher sounds.

Acoustic (sound) signals are air vibrations with different frequencies and strengths. They stimulate the auditory receptors located in the cochlea of ​​the inner ear. The receptors activate the first auditory neurons, after which sensory information is transmitted to the auditory area of ​​the cerebral cortex through a number of sequential sections:

Outer ear - the auditory canal conducts sound vibrations to the eardrum. The eardrum, which separates the outer ear from the tympanic cavity, or middle ear, is a thin (0.1 mm) partition shaped like an inward funnel. The membrane vibrates under the action of sound vibrations coming to it through the external auditory canal.

In the middle ear, filled with air, there are three bones: the hammer, the incus and the stapes, which sequentially transmit vibrations of the eardrum to the inner ear. The hammer is woven into the eardrum with a handle; its other side is connected to the anvil, which transmits vibrations to the stapes. Due to the peculiarities of the geometry of the auditory ossicles, vibrations of the eardrum of reduced amplitude but increased strength are transmitted to the stapes.

There are two muscles in the middle ear: the tensor tympani and the stapedius. The first of them, contracting, increases the tension of the eardrum and thereby limits the amplitude of its vibrations during strong sounds, and the second fixes the stapes and thereby limits its movements. This automatically protects the inner ear from overload;

The inner ear contains the cochlea, which contains auditory receptors. The cochlea is a bony spiral canal forming 2.5 turns. Inside the middle canal of the cochlea, on the main membrane, there is a sound-perceiving apparatus - a spiral organ containing receptor hair cells. These cells transform mechanical vibrations into electrical potentials.

Comparative characteristics of the parts of the hearing organ in Appendix 5.

The mechanisms of auditory reception are as follows. Sound, which is vibrations of air, enters the external auditory canal in the form of air waves through the auricle and acts on the eardrum. Vibrations of the eardrum are transmitted to the auditory ossicles, the movements of which cause vibration of the oval window membrane. These vibrations are transmitted to the perilymph and endolymph, then perceived by the fibers of the main membrane. High sounds cause vibrations of short fibers, low sounds cause vibrations of longer ones located at the top of the cochlea. These vibrations excite the receptor hair cells of the organ of Corti. Next, the excitation is transmitted along the auditory nerve to the temporal lobe of the cerebral cortex, where the final synthesis and synthesis of sound signals occurs.

The taste sensory system is a collection of sensitive chemical receptors that respond to certain chemicals. Taste, like smell, is based on chemoreception. Chemoreceptors - taste cells - are located at the bottom of the taste bud. They are covered with microvilli that come into contact with substances dissolved in water.

Taste buds carry information about the nature and concentration of substances entering the mouth. Their excitation triggers a complex chain of reactions in different parts of the brain, leading to different functioning of the digestive organs or to the removal of substances harmful to the body that enter the mouth with food.

The peripheral section of this system is represented by taste buds - taste receptors - located in the epithelium of the grooved, leaf-shaped and mushroom-shaped papillae of the tongue and in the mucous membrane of the palate, pharynx and epiglottis. Most of them are on the tip, edges and back of the tongue. Each of the approximately 10,000 human taste buds consists of several (2-6) receptor cells and, in addition, supporting cells. The taste bud is flask-shaped; in humans its length and width are about 70 microns. The taste bud does not reach the surface of the mucous membrane of the tongue and is connected to the oral cavity through the taste pore.

The conduction section of this analyzer is represented by the trigeminal nerve, the chorda tympani, the glossopharyngeal nerve, the nuclei of the medulla oblongata, and the nuclei of the thalamus.

The central section (cortical end) of the taste analyzer is located in the evolutionarily ancient formations of the cerebral hemispheres, located on their medial (middle) and lower surfaces. This is the cortex of the hippocampus (Ammon's horn), parahippocampus and uncinate, as well as the lateral part of the postcentral gyrus (Fig. 5.3).

Rice. 5.3. Fornix and hippocampus:

1 - hook; 9 - dentate gyrus; 2 - parahippocampal gyrus; 3 - hippocampal peduncle; 4 - hippocampus; 5 - corpus callosum; 6 - central groove; 7 - occipital lobe; 8 - parietal lobe; 9 - temporal lobe

The conductors of all types of taste sensitivity are the chorda tympani and the glossopharyngeal nerve, the nuclei of which in the medulla oblongata contain the first neurons of the taste system. Many of the fibers coming from taste buds are distinguished by a certain specificity, since they respond by increasing the frequency of pulse discharges only to the action of salt, acid and quinine. Other fibers respond to sugar. The most convincing hypothesis is that information about the 4 main taste sensations: bitter, sweet, sour and salty is encoded not by impulses in single fibers, but by different distributions of discharge frequencies in a large group of fibers, differently excited by the taste substance.

Taste afferent signals enter the nucleus of the solitary fasciculus of the brainstem. From the nucleus of the solitary fasciculus, the axons of the second neurons ascend as part of the medial lemniscus to the arcuate nucleus of the thalamus, where third neurons are located, the axons of which are sent to the cortical taste center. The research results do not yet allow us to assess the nature of the transformations of taste afferent signals at all levels of the taste system.

Olfactory analyzer. The peripheral section of the olfactory sensory system is located in the upper posterior nasal cavity - this is the olfactory epithelium, which contains olfactory cells that interact with molecules of odorant substances.

The conduction section is represented by the olfactory nerve, olfactory bulb, olfactory tract, and the nuclei of the amygdala complex.

The central, cortical section is the uncus, the hippocampal gyrus, the septum pellucidum and the olfactory gyrus.

The nuclei of the taste and olfactory analyzers are closely connected with each other, as well as with the brain structures responsible for the formation of emotions and long-term memory. From here it is clear how important the normal functional state of the taste and olfactory analyzer is.

The olfactory receptor cell is a bipolar cell, at the apical pole of which there are cilia, and an unmyelinated axon extends from its basal part. The receptor axons form the olfactory nerve, which penetrates the base of the skull and enters the olfactory bulb.

Molecules of odorous substances enter the mucus produced by the olfactory glands with a constant flow of air or from the oral cavity during eating. Sniffing accelerates the flow of odorous substances to the mucus.

Each olfactory cell has only one type of membrane receptor protein. This protein itself is capable of binding many odorous molecules of various spatial configurations. The rule “one olfactory cell - one olfactory receptor protein” greatly simplifies the transmission and processing of information about odors in the olfactory bulb - the first nerve center for switching and processing chemosensory information in the brain.

The peculiarity of the olfactory system is, in particular, that its afferent fibers do not switch in the thalamus and do not move to the opposite side of the cerebrum. The olfactory tract emerging from the bulb consists of several bundles that are sent to different parts of the forebrain: the anterior olfactory nucleus, the olfactory tubercle, the prepiriform cortex, the periamygdala cortex and part of the nuclei of the amygdala complex. The connection of the olfactory bulb with the hippocampus, piriform cortex and other parts of the olfactory brain occurs through several switches. It has been shown that the presence of a significant number of centers of the olfactory brain is not necessary for the recognition of odors, therefore, most of the nerve centers into which the olfactory tract is projected can be considered as associative centers that ensure the connection of the olfactory sensory system with other sensory systems and the organization on this basis of a number of complex forms behavior - food, defensive, sexual, etc.

The sensitivity of the human olfactory system is extremely high: one olfactory receptor can be excited by one molecule of an odorant, and the stimulation of a small number of receptors leads to the appearance of sensation. Adaptation in the olfactory system occurs relatively slowly (tens of seconds or minutes) and depends on the speed of air flow over the olfactory epithelium and on the concentration of the odorous substance.

The somatosensory system (musculocutaneous sensory system) includes the skin sensitivity system and the sensitive system of the musculoskeletal system, which are corresponding receptors located in different layers of the skin. The receptor surface of the skin is huge (1.4-2.1 m2). There are many receptors concentrated in the skin. They are localized at different depths of the skin and are distributed unevenly over its surface.

The peripheral part of this important sensory system is represented by a variety of receptors, which, according to their location, are divided into skin receptors, proprioceptors (receptors of muscles, tendons and joints) and visceral receptors (receptors of internal organs). Based on the nature of the perceived stimulus, mechanoreceptors, thermoreceptors, chemoreceptors and pain receptors - nociceptors - are distinguished.

The role of a sense organ here, in fact, is the entire surface of the human body, its muscles, joints, and, to a certain extent, internal organs.

The conduction section is represented by numerous afferent fibers, centers of the dorsal horns of the spinal cord, nuclei of the medulla oblongata, and thalamic nuclei.

The central section is located in the parietal lobe: the primary cortex is in the posterior central gyrus, the secondary cortex is in the superior parietal lobule.

The skin has several analyzer systems: tactile (touch sensations), temperature (sensations of cold and heat), pain. The tactile sensitivity system is unevenly distributed throughout the body. But most of all, the accumulation of tactile cells is observed in the palm of the hand, on the tips of the fingers and on the lips. Tactile sensations of the hand, combining with muscle-joint sensitivity, form the sense of touch - a specifically human system of cognitive activity of the hand, developed through labor.

If you touch the surface of the body and then press on it, the pressure can cause pain. Thus, tactile sensitivity provides knowledge about the qualities of an object, and painful sensations signal the body about the need to move away from the stimulus and have a pronounced emotional tone.

The third type of skin sensitivity - temperature sensations - is associated with the regulation of heat exchange between the body and the environment. The distribution of heat and cold receptors on the skin is uneven. The back is most sensitive to cold, the chest is the least sensitive.

The position of the body in space is signaled by static sensations. Static sensitivity receptors are located in the vestibular apparatus of the inner ear. Sudden and frequent changes in body position relative to the plane of the earth can lead to dizziness.

Mechanisms of excitation of skin receptors: the stimulus leads to deformation of the receptor membrane, as a result of which the electrical resistance of the membrane decreases. An ionic current begins to flow through the receptor membrane, leading to the generation of a receptor potential. When the receptor potential increases to a critical level, impulses are generated in the receptor, propagating along the fiber to the central nervous system.

Conclusion

Thus, information about the surrounding world is perceived by a person through the senses, called sensory systems (analyzers) in physiology.

The activity of analyzers is associated with the emergence of five senses - vision, hearing, taste, smell and touch, through which the body communicates with the external environment.

Sense organs are complex sensory systems (analyzers), including perceptive elements (receptors), nerve pathways and corresponding sections in the brain, where the signal is converted into sensation. The main characteristic of the analyzer is sensitivity, which is characterized by the value of the sensation threshold.

The main functions of the sensory system: detection and discrimination of signals; transmission and conversion of signals; information coding; signal detection and pattern recognition.

Each sensory system includes three sections: 1) peripheral or receptor, 2) conductive, 3) cortical.

Sensory systems perceive signals from the outside world and carry to the brain the information necessary for the body to navigate the external environment and to assess the state of the body itself. These signals arise in perceptive elements - sensory receptors that receive stimuli from the external or internal environment, nerve pathways, and are transmitted from the receptors to the brain and those parts of the brain that process this information - through chains of neurons and the nerve fibers of the sensory system connecting them.

Signal transmission is accompanied by multiple transformations and recoding at all levels of the sensory system and ends with the recognition of a sensory image.

Bibliography

1. Atlas of human anatomy: textbook. allowance for medical textbook establishments / ed. T.S. Artemyev, A.A. Vlasova, N.T. Shindina. - M.: RIPOL CLASSIC, 2007. - 528 p.

2. Fundamentals of psychophysiology: Textbook / Rep. ed. Yu.I. Alexandrov. - St. Petersburg: Peter, 2003. - 496 p.

3. Ostrovsky M.A. Human physiology. Textbook. In 2 vols. T. 2 / M.A. Ostrovsky, I.A. Shevelev; Ed. V.M. Pokrovsky, G.F. Briefly. - M. - 368 p. - P. 201-259.

4. Rebrova N.P. Physiology of sensory systems: Educational manual / N.P. Rebrova. - St. Petersburg: NP “Strategy of the Future”, 2007. - 106 p.

5. Serebryakova T.A. Physiological foundations of mental activity: Textbook. - N.-Novgorod: VGIPU, 2008. - 196 p.

6. Smirnov V.M. Physiology of sensory systems and higher nervous activity: Proc. allowance / V.M. Smirnov, S.M. Budylina. - M.: Academy, 2009. - 336 p. - pp. 178-196.

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8. Physiology of sensory systems and higher nervous activity: textbook. In 2 vols. T. 1. / Ed. Ya.A. Altman, G.A. Kulikova. - M. Academy, 2009. - 288 p.

9. Human physiology / Ed. V.M. Smirnova - M.: Academy, 2010. - p.364-370, 372-375,377-378, 370-371,381-386.

Annex 1

Types of analyzers

Analyzer	Functions (what stimuli it perceives)	Peripheral department	Wiring department	Central department
Visual	Light	Retinal photoreceptors	Optic nerve	Visual area in the occipital lobe of the cerebral cortex
Auditory	Sound	Auditory receptors of the organ of Corti	Auditory nerve	Auditory zone in the temporal lobe of the CBP
Vestibular (gravitational)	Mechanical	Receptors of the semicircular canals and otolithic apparatus	Vestibular, then auditory nerve	Vestibular zone in the temporal lobe of the CBP
Sensorimotor sensitive (somatosensory)	Mechanical, temperature, pain.	Touch receptors in the skin	Spinothalamic tract: cutaneous sensory nerves	Somatosensory area in the posterior central gyrus of the GBP
Sensorimotor motor (motor)	Mechanical	Proprioceptors of muscles and joints	Sensory nerves of the musculoskeletal system	Somatosensory area and motor area in the anterior central gyrus of the GBP
Olfactory	Gaseous chemicals	Olfactory receptors in the nasal cavity	Olfactory nerve	Olfactory nuclei and olfactory centers of the temporal lobe of the CBP
Flavoring	Chemical solutes	Taste buds in the mouth	Facial glossopharyngeal nerve	Taste zone in the parietal lobe of the KBP
Visceral (internal environment)	Mechanical	Interoreceptors of internal organs	Vagus, splanchnic and pelvic nerves	Limbic system and sensorimotor area KBP

Appendix 2

Comparative characteristics of the peripheral section of analyzers

Analyzers	Sensitive organ	Quality	Receptors
Visual analyzer	Retina	Brightness, contrast, motion, size, color	Rods and cones
Hearing analyzer		Height, timbre of sound	Hair cells
Vestibular analyzer	Vestibular organ	Force of gravity	Vestibular cells
Vestibular analyzer	Vestibular organ	Rotation	Vestibular cells
Skin analyzer		Touch	Touch, cold and heat receptors
Taste analyzer		Sweet and sour taste	Taste buds on the tip of the tongue
Taste analyzer		Bitter and salty taste	Taste buds at the base of the tongue
Olfactory analyzer	Olfactory nerves		Olfactory receptors

Comparative characteristics of the conductor and central sections of the analyzers

Analyzers	Switching levels: primary	Switching levels secondary	Switching levels: tertiary	Central department
Visual analyzer	Retina		Primary and secondary visual cortex	Occipital lobes of the brain
Hearing analyzer	Cochlear nuclei		Primary auditory cortex	Temporal lobe of the brain
Vestibular analyzer	Vestibular nuclei		Somatosensory cortex	Parietal and temporal lobes of the brain
Skin analyzer	Spinal cord		Somatosensory cortex	Superior portion of the posterior central gyrus of the brain
Olfactory analyzer	Olfactory bulb	Piriform bark	Limbic system, hypothalamus	Temporal lobe (seahorse cortex) of the brain
Taste analyzer	Medulla		Somatosensory cortex	Inferior portion of the posterior central gyrus of the brain

Appendix 3

Cortical analyzers of the human brain and their functional connection with various organs

1 - peripheral link; 2 - conductive; 3 - central, or cortical; 4 - interoreceptive; 5 - motor; 6 - gustatory and olfactory; 7 - cutaneous, 8 - auditory, 9 - visual)

Appendix 4

Comparative characteristics of the membranes of the eyeball

Shells		Structural features
	Sclera (albuginea)		Supportive, protective
Fibrous casing (outer casing)	Cornea	Transparent, connective tissue, convex in shape	Transmits and refracts light rays
	The choroid itself	Contains many blood vessels	Uninterrupted power supply to the eyes
Choroid (tunica media)	Ciliary body	Contains ciliary muscle	Change in lens curvature
Choroid (tunica media)		Contains the pupil, muscles and melanin pigment	Transmits light rays and determines eye color
	Retina (inner layer)	Two layers: outer pigment (contains fuscin pigment) and inner photosensitive (contains rods, cones)	Converts light stimulation into a nerve impulse, primary processing of the visual signal
Shells		Structural features
Fibrous casing (outer casing)	Sclera (albuginea)	Opaque, connective tissue	Supportive, protective

Appendix 5

Comparative characteristics of the parts of the hearing organ

	Structural features
Outer ear	Auricle, external auditory canal	Protective (hairs, earwax), conductive, resonator
Middle ear	Tympanic cavity, tympanic membrane, auditory ossicles (hammer, incus, stapes), auditory (eustachian) tube	Conductive, increasing vibration power, protective (from strong sound vibrations)
Inner ear	The cochlea of ​​the membranous labyrinth, which contains the spiral organ of Corti	Conductive, sound-receiving (spiral organ)

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General information

Adhering to the cognitive approach to describing the psyche, we imagine a person as a kind of system that processes symbols when solving its problems, then we can imagine the most important feature of a person’s individuality - the sensory organization of the personality.

Sensory organization of personality

The sensory organization of a personality is the level of development of individual sensitivity systems and the possibility of their unification. Human sensory systems are his sense organs, like receivers of his sensations, in which the transformation of sensation into perception occurs.

Any receiver has a certain sensitivity. If we turn to the animal world, we will see that the predominant level of sensitivity of any species is a generic characteristic. For example, bats have developed sensitivity to the perception of short ultrasonic pulses, and dogs have olfactory sensitivity.

The main feature of a person’s sensory organization is that it develops as a result of his entire life path. A person’s sensitivity is given to him at birth, but its development depends on the circumstances, desires and efforts of the person himself.

What do we know about the world and ourselves? Where do we get this knowledge? How? The answers to these questions come from the depths of centuries from the cradle of all living things.

Feel

Sensation is a manifestation of a general biological property of living matter - sensitivity. Through sensation there is a psychic connection with the external and internal world. Thanks to sensations, information about all phenomena of the external world is delivered to the brain. In the same way, a loop is closed through sensations to receive feedback about the current physical and partly mental state of the body.

Through sensations we learn about taste, smell, color, sound, movement, the state of our internal organs, etc. From these sensations, holistic perceptions of objects and the whole world are formed.

It is obvious that the primary cognitive process occurs in the human sensory systems and, on its basis, cognitive processes that are more complex in structure arise: perceptions, ideas, memory, thinking.

No matter how simple the primary cognitive process may be, it is precisely it that is the basis of mental activity; only through the “inputs” of sensory systems does the surrounding world penetrate into our consciousness.

Processing sensations

After the brain receives information, the result of its processing is the development of a response action or strategy aimed, for example, at improving physical tone, focusing more attention on the current activity, or setting up an accelerated involvement in mental activity.

Generally speaking, the response or strategy developed at any given time is the best choice of the options available to a person at the time of decision making. However, it is clear that the number of options available and the quality of choice varies from person to person and depends, for example, on:

mental properties of the individual,

strategies for relationships with others,

partly physical condition,

experience, the presence of the necessary information in memory and the ability to retrieve it.

degree of development and organization of higher nervous processes, etc.

For example, a baby goes out undressed into the cold, his skin feels cold, perhaps a chill appears, he becomes uncomfortable, a signal about this goes to the brain and a deafening roar is heard. An adult's reaction to cold (stimulus) may be different; he will either rush to get dressed, or jump into a warm room, or try to warm up in another way, for example, by running or jumping.

Improving higher mental functions of the brain

Over time, children improve their reactions, greatly increasing the effectiveness of the results achieved. But after growing up, opportunities for improvement do not disappear, despite the fact that an adult’s sensitivity to them decreases. This is exactly what “Effecton” sees as part of its mission: increasing the efficiency of intellectual activity by training the higher mental functions of the brain.

Effecton's software products allow you to measure various indicators of the human sensorimotor system (in particular, the Jaguar package contains time tests for simple audio and visual-motor reactions, complex visual-motor reactions, and accuracy of perception of time intervals). Other packages of the Effecton complex evaluate the properties of cognitive processes at higher levels.

Therefore, it is necessary to develop the child’s perception, and using the “Jaguar” package can help you with this.

Physiology of sensations

Analyzers

The physiological mechanism of sensations is the activity of nervous apparatus - analyzers, consisting of 3 parts:

receptor - the perceiving part of the analyzer (converts external energy into a nervous process)

central section of the analyzer - afferent or sensory nerves

cortical sections of the analyzer, in which nerve impulses are processed.

Certain receptors correspond to their own areas of cortical cells.

The specialization of each sense organ is based not only on the structural features of the analyzer-receptors, but also on the specialization of the neurons that are part of the central nervous apparatus, which receive signals perceived by the peripheral sense organs. The analyzer is not a passive receiver of energy; it reflexively adapts under the influence of stimuli.

Movement of a stimulus from the external to the internal world

According to the cognitive approach, the movement of a stimulus during its transition from the external world to the internal world occurs as follows:

the stimulus causes certain energy changes in the receptor,

energy is converted into nerve impulses,

information about nerve impulses is transmitted to the corresponding structures of the cerebral cortex.

Sensations depend not only on the capabilities of the human brain and sensory systems, but also on the characteristics of the person himself, his development and condition. When sick or tired, a person's sensitivity to certain influences changes.

There are also cases of pathologies when a person is deprived, for example, of hearing or vision. If this problem is congenital, then there is a disruption in the flow of information, which can lead to mental development delays. If these children were taught special techniques that compensate for their deficiencies, then some redistribution within the sensory systems is possible, thanks to which they will be able to develop normally.

Properties of sensations

Each type of sensation is characterized not only by specificity, but also has common properties with other types:

quality,

intensity,

duration,

spatial localization.

But not every irritation causes a sensation. The minimum magnitude of the stimulus at which sensation appears is the absolute threshold of sensation. The value of this threshold characterizes absolute sensitivity, which is numerically equal to a value inversely proportional to the absolute threshold of sensations. And sensitivity to changes in the stimulus is called relative or difference sensitivity. The minimum difference between two stimuli that causes a slightly noticeable difference in sensation is called the difference threshold.

Based on this, we can conclude that it is possible to measure sensations. And once again you are amazed by the amazing, finely working instruments - human sense organs or human sensory systems.

Effecton's software products allow you to measure various indicators of the human sensory system (for example, the Jaguar package contains speed tests for simple audio and visual-motor reactions, complex visual-motor reactions, accuracy of time perception, accuracy of space perception and many others). Other packages of the Effecton complex also evaluate the properties of cognitive processes at higher levels.

Classification of sensations

Five main types of sensations: vision, hearing, touch, smell and taste - were already known to the ancient Greeks. Currently, ideas about the types of human sensations have been expanded; about two dozen different analyzer systems can be distinguished, reflecting the impact of the external and internal environment on receptors.

The classification of sensations is carried out according to several principles. The main and most significant group of sensations brings information from the outside world to a person and connects him with the external environment. These are exteroceptive - contact and distant sensations; they occur in the presence or absence of direct contact of the receptor with the stimulus. Vision, hearing, and smell are distant sensations. These types of sensations provide orientation in the immediate environment. Taste, pain, tactile sensations are contact.

According to the location of the receptors on the surface of the body, in muscles and tendons or inside the body, they are distinguished accordingly:

exteroception - visual, auditory, tactile and others;

proprioception - sensations from muscles, tendons;

interoception - sensations of hunger, thirst.

During the evolution of all living things, sensitivity has undergone changes from the most ancient to the modern. Thus, distant sensations can be considered more modern than contact ones, but in the structure of the contact analyzers themselves it is also possible to identify more ancient and completely new functions. For example, pain sensitivity is more ancient than tactile sensitivity.

Such classification principles help to group all types of sensations into systems and see their interactions and connections.

Types of sensations

Vision, hearing

Let's look at the different types of sensations, keeping in mind that vision and hearing are the most well studied.

The idea 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 sensory system, which appeared later, replaced the concept of analyzer, including the mechanisms of regulation of its various departments with the help of direct and feedback connections. Along with this, the concept still exists sense organ as a peripheral formation that perceives and partially analyzes environmental factors. The main part of the sensory organ is the receptors, equipped with auxiliary structures that ensure 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 can be considered an organ of taste. When directly exposed to various environmental factors with the participation of analyzers in the body, Feel, which are reflections of the properties of objects in the objective world. The peculiarity of sensations is their modality, those. a set of sensations provided by any one analyzer. Within each modality, in accordance with the type (quality) of the sensory impression, different qualities can be distinguished, or valence. Modalities are, for example, vision, hearing, taste. Qualitative types of modality (valence) for vision are different colors, for taste - the sensation of sour, sweet, salty, bitter.

The activity of analyzers is usually associated with the emergence of five senses - vision, hearing, taste, smell and touch, through which the body communicates 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 the tactile sensations arising from touch, includes the feeling of pressure and vibration. The temperature sense includes sensations of warmth or cold, but there are also more complex sensations, such as sensations of hunger, thirst, sexual need (libido), due to the special (motivational) state of the body. The sense of body position in space is associated with the activity of the vestibular and motor analyzers and their interaction with the visual analyzer. The sensation of pain occupies a special place in sensory function. In addition, we can, although “vaguely,” perceive other changes, not only in the external, but also in the internal environment of the body, and in this case emotionally charged sensations are formed. Thus, coronary spasm in the initial stage of the disease, when pain does not yet occur, can cause a feeling of melancholy and despondency. Thus, there are actually much more structures that perceive irritation from the living environment and the internal environment of the body than is commonly believed.

The classification of analyzers can be based on various characteristics: the nature of the current stimulus, the nature of the sensations that arise, the level of receptor sensitivity, 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 indicators of the internal environment within the physiological norm in a healthy person are usually not perceived subjectively in the form of sensations. Thus, 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 body’s adaptation to various conditions of its life. The significance of these analyzers is studied as part of a physiology course (adaptive regulation of the activity of internal organs). But at the same time, changes in some constants of the internal environment of the body can be perceived subjectively in the form of sensations (thirst, hunger, sexual desire) formed on the basis of biological needs. To satisfy these needs, behavioral responses are activated. For example, when a feeling of thirst arises due to stimulation of osmo- or volume receptors, behavior is formed aimed at searching for and receiving 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 the 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 experiment of D. McLosky, which he performed on himself. Primary afferent fibers from muscle receptors were stimulated by threshold electrical stimuli. An increase in the frequency of impulses of these nerve fibers caused the subject to have subjective sensations of a change in the position of the corresponding limb, although its position did not actually change.

Pain analyzer should be highlighted separately due to its special significance for the body - it carries information about damaging actions. Painful sensations can occur when both extero- and interoreceptors are irritated.

Structural and functional organization of analyzers

According to the presentation of 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 the receptors, the energy of the stimulus is transformed into a nerve impulse, as well as the signal is amplified 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. Thus, the receptors of the visual analyzer are adapted to the perception of light, and the auditory receptors are adapted to perceive sound, etc. That part of the receptor surface from which one afferent fiber receives the 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 ensures 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 by mechanical deformation and 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 tension, osmolarity and pH, glucose levels and other substances). Such receptors are found in the mucous membrane of the tongue and nose, carotid and aortic bodies, hypothalamus and 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, midbrain, medulla oblongata and spinal cord.

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

5. Nociceptors, the excitation of which is accompanied by painful sensations (pain receptors). The irritants of these receptors are mechanical, thermal and chemical (histamine, bradykinin, K +, H +, etc.) factors. Painful stimuli are perceived by free nerve endings, which 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 generated into visual, auditory, gustatory, olfactory and tactile.

By location in the body receptors are divided into extero- and interoreceptors.

Exteroceptors 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), blood vessels and the central nervous system. A variety of interoreceptors are receptors of the musculoskeletal system (proprioceptors) 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.

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

According to structural and functional organization distinguish between primary and secondary receptors. Primary receptors are the sensory endings of the dendrite of the afferent neuron. The neuron body is located in the spinal ganglion or cranial nerve ganglion. 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 secondary receptors there is a special cell that is 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 receptor excitation occurs.

Mechanism of receptor excitation. When a stimulus acts on a receptor cell, a change in the spatial configuration of protein receptor molecules occurs in the protein-lipid layer of the membrane. This leads to a change in the permeability of the membrane to certain ions, most often sodium ions, but in recent years the role of potassium in this process has also been discovered. Ionic currents arise, the membrane charge changes, and a receptor potential (RP) is generated. And then the process of excitation occurs in different receptors in different ways. In the primary sensory receptors, which are the free bare ends of a sensitive neuron (olfactory, tactile, proprioceptive), the RP acts on the adjacent, most sensitive areas of the membrane, where an action potential (AP) is generated, which then spreads in the form of impulses along the nerve fiber. The conversion of external stimulus energy into AP in primary receptors can occur both directly on the membrane and with the participation of some auxiliary structures. This, for example, happens in the Pacinian corpuscle. The receptor here is represented by a bare axon ending, which is surrounded by a connective tissue capsule. When the Pacinian corpuscle is compressed, 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 a transmitter from the presynaptic section of the receptor cell into the synaptic cleft of the receptor-afferent synapse. This transmitter acts on the postsynaptic membrane of the sensitive neuron, causing its depolarization and the formation of a postsynaptic potential, which is called the generator potential (GP). GP, acting on extrasynaptic areas of the membrane of a sensitive neuron, causes the generation of APs. GP can be both de- and hyperpolarizing 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 bioelectric processes that have the properties of a local or local response: they spread with decrement, i.e. with attenuation; the magnitude depends on the strength of irritation, since they obey the “law of force”; the value depends on the rate of increase in the stimulus amplitude over time; can be summed up when applying rapidly successive irritations.

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

Most receptors have so-called background activity, i.e. excitation occurs in them in the absence of any stimuli.

Conductor section of the analyzer includes afferent (peripheral) and intermediate neurons of the stem and subcortical structures of the central nervous system (CNS), which constitute a chain of neurons located in different layers at each level of the CNS. The conduction section ensures the conduction of excitation from receptors to the cerebral cortex and partial processing of information. The conduction of excitation through the conduction section is carried out by two afferent pathways:

1) 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 and medulla oblongata, in the visual thalamus and in the corresponding projection zone of the cerebral cortex);

2) in a nonspecific way, with the participation of the reticular formation. At the level of the brain stem, collaterals extend from a specific pathway 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 carried out slowly through a large number of synapses. Due to collaterals, the hypothalamus and other parts of the limbic system of the brain, as well as motor centers, are included in the excitation process. All this provides the autonomic, 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. “core”, 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 of the cortex are distinguished. Excitation from the corresponding receptors to the primary zones is directed along fast-conducting specific pathways, while activation of the secondary and tertiary (associative) zones occurs along polysynaptic nonspecific pathways. In addition, the cortical zones are interconnected by numerous associative fibers. Neurons are distributed unevenly 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 parts of the visual, auditory and skin analyzers. Afferent impulses with the participation of stellate cells of the cortex (IV layer) are transmitted to pyramidal neurons (III layer), from here the processed signal leaves the cortex to other brain structures.

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

Cortical projections of sensory systems have a topical principle of organization. The volume of the cortical projection is proportional to the receptor density. 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 recording evoked potentials (EP) is used. EP is a type of evoked 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.

Among the general principles of analyzer organization, multi-level and multi-channel systems should be highlighted.

Multilevelness provides the possibility of specialization of different levels and layers of the central nervous system for processing certain types of information. This allows the body to more quickly respond to simple signals that are analyzed at individual intermediate levels.

The existing multichannel nature of analyzer systems is manifested in the presence of parallel neural channels, i.e. in each of the layers and levels there are many nerve elements connected with many 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 the construction of sensory systems creates conditions for fine regulation of perception processes through influences from higher levels to lower ones.

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

The main properties of the analyzers are the following.

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

Sensitivity is assessed using a number of criteria.

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

Discrimination threshold(differential threshold) - a minimal change in the strength of the current 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 the determination of the force of pressure on the palm by the test subject’s sensation. It turned out that when a load of 100 g was applied, it was necessary to add a load of 3 g to feel an increase in pressure, when a load of 200 g was applied, it was necessary to add 6 g, 400 g - 12 g, etc. In this case, the ratio of the increase in the strength of stimulation (L) to the strength of the active stimulus (L) is a constant value (C):

This value is different for different analyzers, in this case it is equal to approximately 1/30 of the strength of the current stimulus. A similar pattern is observed when the strength of the current stimulus decreases.

Intensity of sensations with the same stimulus strength can be different, since it depends on the level of excitability of 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 - constant,

L is the strength of the current stimulus,

L 0 - sensation threshold (absolute threshold).

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

2. Inertia- relatively slow onset and disappearance of sensations. The latent time for the occurrence 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. The persistence of sensations for a certain period after the stimulus is turned off is explained by the phenomenon of aftereffects in the central nervous system - mainly by the circulation of excitation. Thus, a visual sensation does not arise and disappear instantly. The latent period of visual sensation is 0.1 s, the aftereffect time is 0.05 s. Light stimuli (flickers) quickly following one after another can give a feeling of continuous light (the phenomenon of “flickering fusion”). The maximum frequency of light flashes, which are perceived separately, is called the critical flickering frequency, which is greater, the stronger the brightness of the stimulus and the higher the excitability of the central nervous system, and is about 20 flickers per second. Along with this, if two stationary stimuli are projected sequentially with an interval of 20-200 ms onto different parts of the retina, a sensation of object movement arises. This phenomenon is called the “Phi Phenomenon.” This effect is observed even when one stimulus is slightly different in shape from the other. These two phenomena: “flicker fusion” and “Phi-phenomenon” are the basis 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 when still images are presented on the screen in rapid succession at a speed of 18-24 frames per second.

3. Ability sensory system to adaptation with a constant strength of a long-acting stimulus, it mainly consists of a decrease in absolute and an increase in differential sensitivity. This property is inherent in all sections of the analyzer, but it is most clearly manifested at the level of receptors and consists in a change not only in their excitability and impulses, but also in indicators of functional mobility, i.e. in changing the number of functioning receptor structures (P.G. Snyakin). Based on the speed of adaptation, all receptors are divided into quickly and slowly adapting, and sometimes a group of receptors with an average speed 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 through descending influences that change the activity of the underlying structures of the sensory system. Thanks to this, the phenomenon of “tuning” sensory systems to 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 in the environment, the beneficial and negative aspects of their impact on the body. Therefore, dysfunction of external analyzers, especially visual and auditory, makes it extremely difficult to understand the outside world (the outside world is very poor for a blind or deaf person). However, only analytical processes in the central nervous system cannot create a real picture of the environment. The ability of analyzers to interact with each other provides a figurative and holistic view of objects in the external world. For example, we evaluate the quality of a lemon slice 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 holistic image of the perceived object is created. The interaction of analyzers when assessing phenomena and objects also underlies compensation for impaired functions when one of the analyzers is lost. Thus, in blind people the sensitivity of the auditory analyzer increases. Such people can determine the location of large objects and walk around them if there is no extraneous noise. This is done by reflecting sound waves from an object in front. American researchers observed a blind man who quite 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. Thus, listening to music can cause pain relief during dental procedures (audioanalgesia). Noise impairs visual perception; bright light increases the perception of sound volume. The process of interaction between sensory systems can manifest itself at various levels. The reticular formation of the brain stem, the cerebral cortex, plays a particularly important role in this. Many cortical neurons have the ability to respond to complex combinations of signals from different modalities (multisensory convergence), which is very important for cognition of the environment and the evaluation of 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 analyzer departments is coding. In the auditory analyzer, the mechanical vibration of the membrane and other sound-conducting elements is at the first stage converted into a receptor potential, the latter ensures the release of the transmitter 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, at the synapse of which the electrical signal again turns into a chemical signal, 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.

Nervous system codes. IN Computer technology uses 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 larger number of combinations with the same code length. The universal code of the nervous system is nerve impulses that travel along nerve fibers. In this case, 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. The transmission of a signal from one cell to another in all sections of the analyzer is carried out using a chemical code, i.e. various mediators. To store information in the central nervous system, encoding is carried out using structural changes in neurons (memory mechanisms).

Coded characteristics of the stimulus. The analyzers encode the qualitative characteristics of the stimulus (for example, light, sound), the strength of the stimulus, the time of its action, as well as space, i.e. the place of action of the stimulus and its localization in the environment. All sections of the analyzer take part in encoding 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 an adequate stimulus. Thus, a light beam excites only the receptors of the retina; 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 the 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. Moreover, with increasing stimulus strength, 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 may also change; in addition, the strength of the stimulus can be encoded by varying the latency period and reaction time. A strong stimulus reduces the latency period, increases the number of impulses and lengthens the reaction time. Space is encoded by the size of the area over which the receptors are excited; this is spatial encoding (for example, we can easily determine whether a pencil touches the surface of the skin with a sharp or blunt end). Some receptors are more easily excited when a stimulus acts on them at a certain angle (Pacinian corpuscles, retinal receptors), which is an assessment of the direction of action of the stimulus on the receptor. The localization of the action of the stimulus is encoded by the fact that receptors in different parts of the body send impulses to certain areas of the cerebral cortex.

The time of action of the stimulus on the receptor is encoded by the fact that it begins to be excited with the onset 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 encoded accurately enough due to their rapid adaptation and cessation of excitation with a constant strength of the stimulus. This inaccuracy is partially compensated by the presence of on-, off- and on-off receptors, which are excited respectively when the stimulus is turned on, 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., sensitization of the receptor to changes in this stimulus develops. An increase in 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 conductor section of the analyzer, coding is carried out only at “switching stations,” that is, when transmitting a signal from one neuron to another, where the code changes. Information is not encoded in nerve fibers; they act as wires through which information encoded in receptors and processed in the centers of the nervous system is transmitted.

There can be different intervals between impulses in a separate nerve fiber, impulses are formed into packets with different numbers, and there can also be different intervals between individual packets. All this reflects the nature of the information encoded in the receptors. In this case, the number of excited nerve fibers in the nerve trunk 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, by changing the volume of impulses at the input and output, and secondly, by spatial coding, i.e. due to the connection of certain neurons with certain receptors. In both cases, the stronger the stimulus, the more neurons are excited.

In the overlying parts of the central nervous system, 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 stimulus parameter, 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 analyzer function. In the sensory nuclei, inhibitory processes occur that filter and differentiate sensory information. These processes provide control of sensory information. This reduces noise and changes the ratio of spontaneous and evoked neuronal activity. This mechanism is realized through 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 arriving in the form of nerve impulses is recoded into structural and biochemical changes in neurons (memory mechanisms). The cerebral cortex carries out the highest analysis and synthesis of incoming information.

Analysis consists in the fact that, with the help of the sensations that arise, we distinguish between the current 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 or phenomenon encountered for the first time.

There are cases where blind people from birth began to see only in adolescence. Thus, a girl who gained sight only at the age of 16 could not use her vision to recognize objects that she had used many times before. But as soon as she took the object in her hands, she happily named it. Thus, she had to practically re-learn the world around her with the participation of the visual analyzer, reinforced by information from other analyzers, in particular from the tactile one. In this case, tactile sensations turned out to be decisive. This is evidenced, for example, by the long-standing experience of Strato. It is known that the image on the retina is reduced and inverted. A newborn sees the world exactly like this. 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 they appear in reality, although the image on the retina remains inverted. Straton put on glasses with lenses that turned the image on the retina to a position corresponding to reality. The observed world around us 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, and 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, incoming information is compared with traces of memory about other similar objects or phenomena. Information received in the form of nerve impulses is encoded using long-term memory mechanisms.

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

sensory receptor visual analyzer

General plan of the structure of sensory systems