To ensure the normal functioning of an organism*, the constancy of its internal environment, connection with the constantly changing external environment and adaptation to it are necessary. The organism receives information about the state of the external and internal environments with the help of those who analyze (distinguish) this information, provide the formation of sensations and ideas, as well as specific forms of adaptive.

The concept of sensory systems was formulated by IP Pavlov in the doctrine of analyzers in 1909 during the study of them. Analyzer- a set of central and peripheral formations that perceive and analyze changes in the external and internal environments of the body. The concept of "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, there is still the concept of "sense organ" as a peripheral entity that perceives and partially analyzes environmental factors. The main part is equipped with auxiliary structures that provide optimal perception.

With the direct impact of various environmental factors with the participation in the body, there are Feel, which are reflections of the properties of objects of the objective world. The peculiarity of sensations is their modality, those. the totality of sensations provided by any one sensory system. Within each modality, in accordance with the type (quality) of the sensory, different qualities can be distinguished, or valency. Modalities are, for example, sight, hearing, taste. Qualitative types of modality (valency) for vision are various colors, for taste - the sensation of sour, sweet, salty, bitter.

The activity of sensory systems is usually associated with the emergence of five senses - sight, hearing, taste, smell and touch, through which the body is connected with the external environment. However, in reality, there are much more of them.

The classification of sensory systems can be based on various features: the nature of the acting stimulus, the nature of the sensations that arise, the level of sensitivity of receptors, the rate of adaptation, and much more.

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

External sensor systems perceive and analyze changes in the external environment. This should include visual, auditory, olfactory, gustatory, tactile and temperature sensory systems, which are perceived subjectively as sensations.

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

Sensory systems of body position 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) sensory systems. As we evaluate the position of our body or its parts relative to each other, this impulse reaches our consciousness. This is evidenced, in particular, by the experience of D. Maklosky, which the scientist put on himself. Primary afferent fibers from muscle receptors were irritated by threshold electrical ones. An increase in the frequency of impulses of these nerve fibers evoked subjective sensations in the subject of a change in the position of the corresponding limb, although its position did not actually change.

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

Interaction of sensory systems carried out at the spinal, reticular, thalamic and cortical levels. The integration of signals in . In the cerebral cortex, the integration of higher-order signals takes place. As a result of multiple connections with other sensory and non-specific systems, many cortical systems acquire the ability to respond to complex combinations of signals of different modalities. This is especially characteristic of the nerve cells of the associative areas of the cerebral cortex, which have high plasticity, which ensures the restructuring of their properties in the process of continuous learning to recognize new stimuli. Intersensory (cross-modal) interaction at the cortical level creates the conditions for the formation of a "scheme of the world" (or "map of the world") and continuous linking, coordination with it of the body's own "scheme" of a given organism.

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

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

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• Introduction
• Conclusion
• Applications
• Introduction
• One of the physiological functions of the body is the perception of the surrounding reality. Obtaining and processing information about the surrounding world is a necessary condition for maintaining the homeostatic constants of the organism and the formation of behavior. Among the stimuli acting on the body, only those for the perception of which there are specialized formations are caught and perceived. Such stimuli are called sensory stimuli, and complex structures designed to process them 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 the sense organs (analyzers) is important not only for organizing the activity of internal organs and behavior in accordance with the requirements of the environment, but also for the full development of a person.

The sense organs are the "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 feel the effect 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 the development and life of a person.
• 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. Obtaining information from the environment and one's own body is a prerequisite for human existence.
• The sensory system (lat. sensus - feeling) is a set of peripheral and central structures of the nervous system, which consists of a group of cells (receptors) responsible for the perception of 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. Budylin. - M.: Academy, 2009. - 304 p. - S. 178-196.
• The term "sensory systems" replaced the name "sense organs", which was retained only to refer to the anatomically isolated peripheral parts of some sensory systems (such as the eye or ear). In 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 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. The perception of stimuli in the receptors occurs through the transformation of the energy of the stimulus into a nerve impulse (this part is the sense organs - the eye, ear, etc.).
• 2. The conduction section of the analyzer includes afferent (peripheral) and intermediate neurons of the stem and subcortical structures of the central nervous system (CNS). It provides the conduction of excitation from receptors to the cerebral cortex. In the conductor department, partial processing of information occurs at the stages of switching (for example, in the thalamus).

3. The central or cortical section of the analyzer consists of two parts: the central part - the "nucleus", - 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 features of the structure of the central department provide the process of compensating for impaired functions. At the level of the cortical region, the highest analysis and synthesis of afferent excitations is 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 section of the analyzers, and a comparative characteristic 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 processing of information. The lowest level of such processing is provided by primary sensory neurons, which are located in specialized sensory organs or in sensitive ganglia and are designed to conduct excitation from peripheral receptors to the central nervous system.
• Peripheral receptors are sensitive, highly specialized formations capable of perceiving, transforming and transmitting the energy of an external stimulus to primary sensory neurons. The central processes of primary sensory neurons terminate in the brain or spinal cord on second-order neurons, whose bodies are located in the switching nucleus. It contains not only excitatory, but also inhibitory neurons involved in the processing of transmitted information.
• Representing a higher hierarchical level, the neurons of the switching nucleus can regulate the transmission of information by amplifying some and inhibiting or suppressing other signals. Axons of neurons of the second order 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 feedbacks addressed to the receptor or the first central section. Activating them makes it possible to regulate the process of perception of information and its conduction along the ascending pathways in the brain.

• Each individual sensory system responds 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 led to the concept of "modality". A stimulus of this modality, adequate for a particular sensory system, is considered to be such a stimulus that causes a reaction at a minimum physical intensity. By modality, stimuli are divided into mechanical, chemical, thermal, light, etc.
• All sensory systems, regardless of the nature of the acting 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 for the design of sensor systems / A.S. Batuev. - St. Petersburg: Peter, 2010. - S. 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 transmission of information.

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

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

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

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

7. The principle of bilateral symmetry (exists in a relative degree).

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

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

1. Detection of signals begins in the receptor - a specialized cell, evolutionarily adapted to the perception of a stimulus of a certain modality from the external or internal environment and its transformation 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 the neurons of the entire sensory system are involved in this process. 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 fast analysis. Signal transformations can be conditionally divided into spatial and temporal. Among the spatial transformations, changes in the ratio of different parts of the signal are distinguished.

4. Coding of information is called the transformation of information into a conditional form - a code, performed according to certain rules. In a sensory system, signals are encoded by a binary code, that is, by the presence or absence of an electrical impulse at one time or another. Information about the stimulation and its parameters is transmitted in the form of individual impulses, as well as groups or "packages" 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 frequency, the duration of bursts and intervals between them, as well as the temporal “pattern” of a 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 by the place of excitation in the neuronal layer.

5. Signal detection is the selective selection by a sensory neuron of one or another sign of a stimulus that has behavioral significance. Such an analysis is carried out by detector neurons that selectively respond only to certain parameters of the stimulus. 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 slopes of the same strip, other neurons will respond. In the higher parts of the sensory system, detectors of complex features and whole images are concentrated.

6. Pattern recognition is the final and most complex operation of the sensory system. It consists in assigning the image to one or another class of objects that the organism encountered earlier, i.e., in the classification of images. By synthesizing signals from neurons-detectors, the higher part of the sensory system forms an "image" of the stimulus and compares it with a multitude of images stored in memory. Recognition ends with a decision about which object or situation the organism encountered. As a result of this, perception occurs, that is, we are aware of whose face we see in front of us, whom we hear, what smell we smell. Recognition often occurs regardless of signal variability. So, we reliably identify objects in their 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.

Cortical analyzers of the human cerebrum, and their functional connection with various organs, are clearly shown in the figure in Appendix 3.

Human sensory systems provide:

1) the formation of sensations and the perception of existing 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 wake up.

The process of transmission of 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 the 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). A sensation is a subjective sensory response to an actual sensory stimulus (eg, a sensation of light, warmth or cold, touch, etc.). as mentioned earlier, the totality of sensations provided by any one analyzer is denoted by the term "modality", which may include various qualitative types of sensations. Independent modalities are touch, sight, hearing, smell, taste, feeling of cold or heat, pain, vibration, sensation of the position of the limbs and muscle load. Within the modalities there are different qualities or submodalities; for example, taste modality distinguishes between sweet, salty, sour, and bitter tastes.

On the basis of 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, memory of past sensory experience and 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, its transformation into nerve signals and their transmission to the brain through chains of neurons. The process of transmission of sensory signals is accompanied by their multiple 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 analyzers of a person react to those stimuli that come from the external environment. The internal analyzers of a person are those structures that respond to changes within the body. For example, in muscle tissue there are 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: sight, hearing and smell.

The activity of each of the sense organs is 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 tubercles of the quadrigemina into the primary and secondary visual cortex;

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

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

d) sense of 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) Non-specific 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 there is excitation of photoreceptors, transmission and transformation of visual information in the neural layers of the visual system, and visual perception ends with the adoption of a decision about the visual image by the higher cortical sections of this system.

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

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

The conductor department of the visual sensory system is the optic nerve, the nuclei of the superior colliculus of the quadrigemina of the midbrain, the nuclei of the external geniculate body of the diencephalon.

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

The eyeball has a spherical shape, which makes it easier to turn to aim at the object in question. The amount of light that enters the retina is regulated by the pupil, which is able to expand and contract. 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. Due 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 - protein shell; 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 membrane of the eye. There are two types of photoreceptors here (rod and cone: cones function in high light conditions, they provide day and color vision; much more light-sensitive rods are responsible for twilight vision) and several types of nerve cells. All of these 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 that is placed on 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 remote 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 sound stimuli are analyzed and evaluated (Fig. 2).

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

Conductor department. Hair cells are covered by nerve fibers of the cochlear branch of the auditory nerve, which carries a nerve impulse to the medulla oblongata, then, crossing with the second neuron of the auditory pathway, it goes to the posterior tubercles of the quadrigemina and the nuclei of the internal geniculate bodies of the diencephalon, and from them to the temporal region of the cortex, where is the central part of the auditory analyzer located.

Figure 2 - Organ of hearing:

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

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

The central part 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 action of strong sounds, the excitability of the sound analyzer decreases, and with a long stay in 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 excite 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 series of successive sections:

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

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

There are two muscles in the middle ear: the tensor tympanic membrane and the stirrup. The first of them, contracting, increases the tension of the tympanic membrane and thereby limits the amplitude of its oscillations during strong sounds, and the second fixes the stirrup and thereby limits its movement. By this, the inner ear is automatically protected from overload;

The cochlea contains the auditory receptors in the inner ear. 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 air vibrations, in the form of air waves, enters the external auditory canal through the auricle and acts on the eardrum. The vibrations of the tympanic membrane are transmitted to the auditory ossicles, the movements of which cause the vibration of the membrane of the oval window. These vibrations are transmitted to the perilymph and endolymph, then perceived by the fibers of the main membrane. High sounds cause oscillations of short fibers, low sounds - longer, located at the top of the cochlea. These vibrations excite the receptor hair cells of the organ of Corti. Further, 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 takes place.

The gustatory 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 from different parts of the brain, leading to different work of the digestive organs or to the removal of substances harmful to the body that have entered the mouth with food.

The peripheral part of this system is represented by taste buds - taste receptors - located in the epithelium of the grooved, foliate and mushroom 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, of 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 conductor section of this analyzer is represented by the trigeminal nerve, the tympanic string, 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 hook, 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 - leg of the hippocampus; 4 - hippocampus; 5 - corpus callosum; 6 - central furrow; 7 - occipital lobe; 8 - parietal lobe; 9 - temporal lobe

The conductors of all types of taste sensitivity are the tympanic string 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 the taste buds are distinguished by a certain specificity, since they respond with an increase in impulse discharges only to the action of salt, acid and quinine. Other fibers react to sugar. The most convincing is the hypothesis according to which information about the 4 main taste sensations: bitter, sweet, sour and salty is encoded not by impulses in single fibers, but by a different distribution of the discharge frequency in a large group of fibers differently excited by the taste substance.

Taste afferent signals enter the nucleus of a single bundle of the brainstem. From the nucleus of a single bundle, the axons of the second neurons ascend as part of the medial loop to the arcuate nucleus of the thalamus, where the third neurons are located, the axons of which are directed to the cortical center of taste. The results of the studies do not yet allow us to assess the nature of the transformations of gustatory afferent signals at all levels of the gustatory system.

Olfactory analyzer. The peripheral part of the olfactory sensory system is located in the upper-posterior nasal cavity, it is the olfactory epithelium, in which there are olfactory cells that interact with molecules of odorous substances.

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

The central, cortical section is the hook, the hippocampal gyrus, the transparent septum and the olfactory gyrus.

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

The olfactory receptor cell is a bipolar cell, on the apical pole of which there are cilia, and an unmyelinated axon departs from its basal part. The axons of the receptors 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 meals. 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 able to bind 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.

A feature of the olfactory system is, in particular, that its afferent fibers do not switch in the thalamus and do not pass to the opposite side of the cerebrum. The olfactory tract leaving the bulb consists of several bundles that go 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 is carried out 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 odorous substance, and the excitation of a small number of receptors leads to a sensation. Adaptation in the olfactory system occurs relatively slowly (tens of seconds or minutes) and depends on the air flow velocity over the olfactory epithelium and on the concentration of the odorous substance.

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

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

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

The conductor section is represented by numerous afferent fibers, centers of the posterior horns of the spinal cord, nuclei of the medulla oblongata, and nuclei of the thalamus.

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

There are several analyzer systems in the skin: tactile (sensations of touch), temperature (sensations of cold and heat), and pain. The system of tactile sensitivity is unevenly distributed throughout the body. But most of all, the accumulation of tactile cells is observed on the palm, on the fingertips and on the lips. The tactile sensations of the hand, combined with the muscular-articular sensitivity, form the sense of touch - a specifically human system of cognitive activity of the hand developed in labor.

If you touch the surface of the body, then press on it, the pressure can cause pain. Thus, tactile sensitivity provides knowledge about the qualities of an object, and pain 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 transfer 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 least - the chest.

Static sensations signal the position of the body in space. Static sensitivity receptors are located in the vestibular apparatus of the inner ear. Sudden and frequent changes in body position relative to the ground plane 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 ion current begins to flow through the receptor membrane, leading to the generation of the receptor potential. When the receptor potential increases to a critical level in the receptor, impulses are generated that propagate along the fiber in the CNS.

Conclusion

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

The activity of the analyzers is associated with the emergence of five senses - sight, hearing, taste, smell and touch, with the help of which the organism is connected 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 are: detection and discrimination of signals; transmission and conversion of signals; information encoding; 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 in the external environment and to assess the state of the body itself. These signals arise in the perceiving 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 the chains of neurons and the nerve fibers of the sensory system that connect them.

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

Bibliography

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

2. Fundamentals of psychophysiology: Textbook / Ed. 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. - S. 201-259.

4. Rebrova N.P. Physiology of sensory systems: Educational and methodological manual / N.P. Rebrova. - St. Petersburg: NP "Future Strategy", 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. Budylin. - M.: Academy, 2009. - 336 p. - S. 178-196.

7. Titov V.A. Psychophysiology. Lecture notes / V.A. Titov. - M.: Prior-izdat, 2003. - 176 p.

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

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

Appendix 1

Types of analyzers

Analyzer	Functions (what stimuli it perceives)	Peripheral department	conductor department	Central department
Visual	light	Retinal photoreceptors	optic nerve	Visual zone in the occipital lobe of the cerebral cortex
Auditory	Sound	Auditory receptors in the organ of Corti	Auditory nerve	The auditory zone in the temporal lobe of the CBP
Vestibular (gravitational)	Mechanical	Receptors of the semicircular canals and ottolith apparatus	Vestibular then auditory nerve	Vestibular zone in the temporal lobe of the CBP
Sensorimotor sensitive (somatosensory)	Mechanical, thermal, pain.	touch receptors in the skin	Spinothalamic pathway: nerves of skin sensation	Somatosensory zone in the posterior central gyrus of the CBP
Sensorimotor motor (motor)	Mechanical	Proprioreceptors in muscles and joints	Sensory nerves of the musculoskeletal system	Somatosensory zone and motor zone in the anterior central gyrus of the CBP
Olfactory	Gaseous chemicals	Olfactory receptors in the nasal cavity	Olfactory nerve	Olfactory nuclei and olfactory centers of the temporal lobe of the CBP
Taste	Chemical solutes	Taste buds in the mouth	Facial glossopharyngeal nerve	Taste zone in the parietal lobe of the CBP
Visceral (internal environment)	Mechanical	Interoreceptors of internal organs	Vagus, celiac and pelvic nerves	Limbic system and sensorimotor area

Appendix 2

Comparative characteristics of the peripheral section of the analyzers

Analyzers	sensitive organ	Quality	Receptors
visual analyzer	Retina	Brightness, Contrast, Motion, Size, Color	Rods and cones
auditory 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 at 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 conductive and central sections of the analyzers

Analyzers	Switch levels: primary	Switch levels secondary	Switch levels: tertiary	Central department
visual analyzer	Retina		Primary and secondary visual cortex	Occipital lobes of the brain
auditory analyzer	snail kernels		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 (cortex of the seahorse gyrus) of the brain
Taste Analyzer	Medulla		Somatosensory cortex	Inferior portion of the posterior central gyrus of the brain

Annex 3

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

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

Appendix 4

Comparative characteristics of the membranes of the eyeball

Shells		Structural features
	Sclera (protein coat)		Support, protective
Fibrous sheath (outer sheath)	Cornea	Transparent, connective tissue, has a convex shape	Transmits and refracts light rays
	The choroid proper	Contains many blood vessels	Uninterrupted eye supply
Vascular membrane (middle layer)	ciliary body	Contains ciliary muscle	Change in the curvature of the lens
Vascular membrane (middle layer)		Contains pupil, muscle and melanin pigment	Transmits light rays and detects eye color
	Retina (inner shell)	Two layers: outer pigmented (contains the pigment fuscin) and inner light-sensitive (contains rods, cones)	Converts light stimulation into a nerve impulse, primary processing of the visual signal
Shells		Structural features
Fibrous sheath (outer sheath)	Sclera (protein coat)	Opaque, connective tissue	Support, protective

Appendix 5

Comparative characteristics of the parts of the organ of hearing

	Structural features
outer ear	auricle, external auditory meatus	Protective (hairs, earwax), conductive, resonator
Middle ear	Tympanic cavity, tympanic membrane, auditory ossicles (hammer, anvil, stirrup), auditory (Eustachian) tube	Conductor, increase in the power of vibrations, protective (from strong sound vibrations)
inner ear	The cochlea of ​​the membranous labyrinth, which contains the spiral (corti) organ	Conductive, sound-perceiving (spiral organ)

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Properties of the conductor section of the analyzers

This department of analyzers is represented by afferent pathways and subcortical centers. The main functions of the conductor department are: analysis and transmission of information, implementation of reflexes and inter-analyzer interaction. These functions are provided by the properties of the conductive section of the analyzers, which are expressed in the following.

1. From each specialized formation (receptor), there is a strictly localized specific sensory path. These pathways usually transmit signals from receptors of the same type.

2. Collaterals depart from each specific sensory pathway to the reticular formation, as a result of which it is a structure of convergence of various specific pathways and the formation of multimodal or non-specific pathways, in addition, the reticular formation is a place of interanalyzer interaction.

3. There is a multi-channel conduction of excitation from receptors to the cortex (specific and non-specific pathways), which ensures the reliability of information transmission.

4. During the transfer of excitation, there is a multiple switching of excitation at different levels of the central nervous system. There are three main switching levels:

• spinal or stem (medulla oblongata);
• visual tubercle;
• the corresponding projection area of ​​the cerebral cortex.

At the same time, within the sensory pathways, there are afferent channels for the urgent transmission of information (without switching) to higher brain centers. It is believed that through these channels, the pre-adjustment of higher brain centers to the perception of subsequent information is carried out. The presence of such pathways is a sign of improving the design of the brain and increasing the reliability of sensory systems.

5. In addition to specific and non-specific pathways, there are so-called associative thalamo-cortical pathways associated with associative areas of the cerebral cortex. It has been shown that the activity of thalamo-cortical associative systems is associated with an intersensory assessment of the biological significance of the stimulus, etc. Thus, the sensory function is carried out on the basis of the interconnected activity of specific, nonspecific and associative formations of the brain, which ensure the formation of an adequate adaptive behavior of the organism.

Central, or cortical, part of the sensory system , according to I.P. Pavlov, it consists of two parts: central part, i.e. "nucleus", represented by specific neurons that process afferent impulses from receptors, and 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 cortical zones are distinguished. Excitation from the corresponding receptors to the primary zones is directed along fast-conducting specific pathways, while the activation of secondary and tertiary (associative) zones occurs along polysynaptic non-specific pathways. In addition, the cortical zones are interconnected by numerous associative fibers.

CLASSIFICATION OF RECEPTORS

The classification of receptors is based primarily on on the nature of feelings that arise in a person when they are irritated. Distinguish visual, auditory, olfactory, gustatory, tactile receptors thermoreceptors, proprio and vestibuloreceptors (receptors of the position of the body and its parts in space). The question of the existence of special pain receptors .

Receptors by location divided into external , or exteroreceptors, and internal , or interoreceptors. Exteroreceptors include auditory, visual, olfactory, taste and tactile receptors. Interoreceptors include vestibuloreceptors and proprioreceptors (receptors of the musculoskeletal system), as well as interoreceptors that signal the state of internal organs.

By the nature of contact with the external environment receptors are divided into distant receiving information at a distance from the source of irritation (visual, auditory and olfactory), and contact - excited by direct contact with the stimulus (gustatory and tactile).

Depending on the nature of the type of perceived stimulus , to which they are optimally tuned, there are five types of receptors.

· Mechanoreceptors excited by their mechanical deformation; located in the skin, blood vessels, internal organs, musculoskeletal system, auditory and vestibular systems.

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

· thermoreceptors react to temperature changes. They are divided into heat and cold receptors and are found in the skin, mucous membranes, blood vessels, internal organs, hypothalamus, middle, medulla and spinal cord.

· Photoreceptors in the retina, the eyes perceive light (electromagnetic) energy.

· Nociceptors , the excitation of which is accompanied by pain 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 that are found in the skin, muscles, internal organs, dentin, and blood vessels. From a psychophysiological point of view, receptors are divided into visual, auditory, gustatory, olfactory and tactile.

Depending on the structure of the receptors they are subdivided into primary , or primary sensory, which are specialized endings of a sensitive neuron, and secondary , or secondary-sensing, which are cells of epithelial origin, capable of generating a receptor potential in response to the action of an adequate stimulus.

Primary sensory receptors can themselves generate action potentials in response to stimulation by an adequate stimulus, if the value of their receptor potential reaches a threshold value. These include olfactory receptors, most skin mechanoreceptors, thermoreceptors, pain receptors or nociceptors, proprioceptors, and most internal organ interoreceptors. The body of the neuron is located in the spinal ganglion or in the ganglion of the cranial nerves. In the primary receptor, the stimulus acts directly on the endings of the sensory neuron. Primary receptors are phylogenetically more ancient structures, they include olfactory, tactile, temperature, pain receptors and proprioceptors.

Secondary sensory receptors respond to the action of the stimulus only by the appearance of a receptor potential, the magnitude of which determines the amount of mediator secreted by these cells. With its help, secondary receptors act on the nerve endings of sensory neurons that generate action potentials depending on the amount of mediator released from the secondary sensory receptors. In secondary receptors there is a special cell synaptically connected to the end of the dendrite of the sensory neuron. This is a cell, such as a photoreceptor, of epithelial nature or neuroectodermal origin. Secondary receptors are represented by taste, auditory and vestibular receptors, as well as chemosensitive cells of the carotid glomerulus. Retinal photoreceptors, which have a common origin with nerve cells, are more often referred to as primary receptors, but their lack of the ability to generate action potentials indicates their similarity to secondary receptors.

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

Most receptors are excited in response to the action of stimuli of only one physical nature and therefore belong to monomodal . They can also be excited by some inadequate stimuli, for example, photoreceptors - by strong pressure on the eyeball, and taste buds - by touching the tongue to the contacts of a galvanic battery, but it is impossible to obtain qualitatively distinguishable sensations in such cases.

Along with monomodal, there are polymodal receptors, adequate stimuli of which can serve as stimuli of a different nature. To this type of receptors belong some pain receptors, or nociceptors (lat. nocens - harmful), which can be excited by mechanical, thermal and chemical stimuli. Polymodality is present in thermoreceptors that respond to an increase in the concentration of potassium in the extracellular space in the same way as to an increase in temperature.

Visual perception begins with the projection of an image onto the retina and excitation of photoreceptors, then the information is sequentially processed in the subcortical and cortical visual centers, resulting in a visual image that, due to the interaction of the visual analyzer with other analyzers, fairly correctly reflects objective reality. Visual sensory system - a sensory system that provides: - coding of visual stimuli; and hand-eye coordination. Through the visual sensory system, animals perceive objects and objects of the outside world, the degree of illumination and the length of daylight hours.

The visual sensory system, like any other, consists of three departments:

1. Peripheral department - the eyeball, in particular - the retina of the eye (perceives light irritation)

2. Conductor department - axons of ganglion cells - optic nerve - optic chiasm - optic tract - diencephalon (geniculate bodies) - midbrain (quadrigemina) - thalamus

3. The central section - the occipital lobe: the region of the spur groove and adjacent convolutions.

optic tract make up several neurons. Three of them - photoreceptors (rods and cones), bipolar cells and ganglion cells - are located in the retina.

After decussation, the optic fibers form optic tracts, which, at the base of the brain, go around the gray tubercle, pass along the lower surface of the legs of the brain and end in the lateral geniculate body, the cushion of the optic tubercle (thalamus opticus) and the anterior quadrigemina. Of these, only the first is a continuation of the visual path and the primary visual center.

At the ganglion cells of the external geniculate body, the fibers of the optic tract end and the fibers of the central neuron begin, which pass through the posterior knee of the internal capsule and then, as part of the Graziole bundle, go to the cortex of the occipital lobe, cortical visual centers, in the region of the spur groove.

So, the nerve path of the visual analyzer begins in the layer of retinal ganglion cells and ends in the cortex of the occipital lobe of the brain and has peripheral and central neurons. The first consists of the optic nerve, chiasm and visual pathways with the primary visual center in the lateral geniculate body. Here begins the central neuron, which ends in the cortex of the occipital lobe of the brain.

The physiological significance of the visual pathway is determined by its function, which conducts visual perception. The anatomical relationships of the central nervous system and the visual pathway determine its frequent involvement in the pathological process with early ophthalmological symptoms, which are of great importance in the diagnosis of diseases of the central nervous system and in the dynamics of monitoring the patient.

For a clear vision of an object, it is necessary that the rays of each of its points be focused on the retina. If you look into the distance, then close objects are not clearly visible, blurry, since the rays from near points are focused behind the retina. It is impossible to see objects equally clearly at different distances from the eye at the same time.

Refraction(ray refraction) reflects the ability of the optical system of the eye to focus the image of an object on the retina. The peculiarities of the refractive properties of any eye include the phenomenon spherical aberration . It lies in the fact that the rays passing through the peripheral parts of the lens are refracted more strongly than the rays passing through its central parts (Fig. 65). Therefore, the central and peripheral rays do not converge at one point. However, this feature of refraction does not interfere with a clear vision of the object, since the iris does not transmit rays and thereby eliminates those that pass through the periphery of the lens. The unequal refraction of rays of different wavelengths is called chromatic aberration .

The refractive power of the optical system (refraction), that is, the ability of the eye to refract, is measured in conventional units - diopters. The diopter is the refractive power of a lens, in which parallel rays, after refraction, are collected at a focus at a distance of 1 m.

We see the world around us clearly when all departments of the visual analyzer "work" harmoniously and without interference. In order for the image to be sharp, the retina must obviously be in the back focus of the optical system of the eye. Various violations of the refraction of light rays in the optical system of the eye, leading to defocusing of the image on the retina, are called refractive errors (ametropia). These include myopia, hyperopia, age-related farsightedness and astigmatism (Fig. 5).

Fig.5. The course of rays in various types of clinical refraction of the eye

a - emetropia (normal);

b - myopia (myopia);

c - hypermetropia (farsightedness);

D - astigmatism.

With normal vision, which is called emmetropic, visual acuity, i.e. the maximum ability of the eye to distinguish individual details of objects usually reaches one conventional unit. This means that a person is able to see two separate points, visible at an angle of 1 minute.

With an anomaly of refraction, visual acuity is always below 1. There are three main types of refractive error - astigmatism, myopia (myopia) and farsightedness (hypermetropia).

Refractive errors cause nearsightedness or farsightedness. The refraction of the eye changes with age: it is less than normal in newborns, in old age it can decrease again (the so-called senile farsightedness or presbyopia).

Astigmatism due to the fact that, due to congenital features, the optical system of the eye (cornea and lens) refracts rays differently in different directions (along the horizontal or vertical meridian). In other words, the phenomenon of spherical aberration in these people is much more pronounced than usual (and it is not compensated by pupil constriction). So, if the curvature of the surface of the cornea in a vertical section is greater than in a horizontal one, the image on the retina will not be clear, regardless of the distance to the object.

The cornea will have, as it were, two main focuses: one for the vertical section, the other for the horizontal. Therefore, the rays of light passing through the astigmatic eye will be focused in different planes: if the horizontal lines of the object are focused on the retina, then the vertical lines are in front of it. Wearing cylindrical lenses, matched to the real defect in the optical system, to a certain extent compensates for this refractive error.

Nearsightedness and farsightedness due to changes in the length of the eyeball. With normal refraction, the distance between the cornea and the central fovea (yellow spot) is 24.4 mm. With myopia (nearsightedness), the longitudinal axis of the eye is more than 24.4 mm, so the rays from a distant object are focused not on the retina, but in front of it, in the vitreous body. To see clearly into the distance, it is necessary to place concave lenses in front of myopic eyes, which will push the focused image onto the retina. In a far-sighted eye, the longitudinal axis of the eye is shortened; less than 24.4 mm. Therefore, rays from a distant object are focused not on the retina, but behind it. This lack of refraction can be compensated by an accommodative effort, i.e. an increase in the convexity of the lens. Therefore, a far-sighted person strains the accommodative muscle, considering not only close, but also distant objects. When viewing close objects, the accommodative efforts of far-sighted people are insufficient. Therefore, for reading, farsighted people should wear glasses with biconvex lenses that enhance the refraction of light.

Refractive errors, in particular myopia and hyperopia, are also common among animals, for example, in horses; myopia is very often observed in sheep, especially cultivated breeds.

Skin receptors

• pain receptors.
• Pacinian corpuscles are encapsulated pressure receptors in a round multilayered capsule. They are located in the subcutaneous fat. They are fast-adapting (they react only at the moment of the beginning of the impact), that is, they register the force of pressure. They have large receptive fields, that is, they represent rough sensitivity.
• Meissner bodies are pressure receptors located in the dermis. They are a layered structure with a nerve ending passing between the layers. They are fast adapting. They have small receptive fields, that is, they represent a subtle sensitivity.
• Merkel discs are non-encapsulated pressure receptors. They are slowly adapting (they respond to the entire duration of exposure), that is, they record the duration of pressure. They have small receptive fields.
• Hair follicle receptors - respond to hair deflection.
• Ruffini's endings are stretch receptors. They are slowly adapting, have large receptive fields.

Basic functions of the skin: The protective function of the skin is the protection of the skin from mechanical external influences: pressure, bruises, tears, stretching, radiation exposure, chemical irritants; immune function of the skin. T-lymphocytes present in the skin recognize exogenous and endogenous antigens; Largenhans cells deliver antigens to the lymph nodes, where they are neutralized; Receptor function of the skin - the ability of the skin to perceive pain, tactile and temperature irritation; The thermoregulatory function of the skin lies in its ability to absorb and release heat; The metabolic function of the skin combines a group of private functions: secretory, excretory, resorption and respiratory activity. Resorption function - the ability of the skin to absorb various substances, including drugs; The secretory function is carried out by the sebaceous and sweat glands of the skin, which secrete lard and sweat, which, when mixed, form a thin film of water-fat emulsion on the surface of the skin; Respiratory function - the ability of the skin to absorb oxygen and release carbon dioxide, which increases with an increase in ambient temperature, during physical work, during digestion, and the development of inflammatory processes in the skin.

Skin structure

Causes of pain. Pain occurs when, firstly, the integrity of the protective integumentary membranes of the body (skin, mucous membranes) and internal cavities of the body (meninges, pleura, peritoneum, etc.) is violated, and, secondly, the oxygen regime of organs and tissues to a level that causes structural and functional damage.

Pain classification. There are two types of pain:

1. Somatic, arising from damage to the skin and the musculoskeletal system. Somatic pain is divided into superficial and deep. Superficial pain is called pain of skin origin, and if its source is localized in the muscles, bones and joints, it is called deep pain. Superficial pain is manifested in tingling, tingling. Deep pain, as a rule, is dull, poorly localized, has a tendency to radiate to surrounding structures, is accompanied by discomfort, nausea, severe sweating, and a drop in blood pressure.

2. Visceral, arising from damage to internal organs and having a similar picture with deep pain.

Projection and reflected pain. There are special types of pain - projection and reflected.

As an example projection pain you can cause a sharp blow to the ulnar nerve. Such a blow causes an unpleasant, hard to describe sensation that spreads to those parts of the hand that are innervated by this nerve. Their occurrence is based on the law of pain projection: no matter what part of the afferent pathway is irritated, pain is felt in the region of the receptors of this sensory pathway. One of the most common causes of projection pain is compression of the spinal nerves at their entry into the spinal cord as a result of damage to the intervertebral cartilage discs. Afferent impulses in nociceptive fibers in such a pathology cause pain sensations that are projected into the area associated with the injured spinal nerve. Projection (phantom) pain also includes pain that patients feel in the area of ​​the remote part of the limb.

Reflected pains pain sensations are called not in the internal organs, from which pain signals are received, but in certain parts of the skin surface (Zakharyin-Ged zones). So, with angina pectoris, in addition to pain in the region of the heart, pain is felt in the left arm and shoulder blade. Reflected pain differs from projection pain in that it is not caused by direct stimulation of nerve fibers, but by irritation of some receptive endings. The occurrence of these pains is due to the fact that the neurons that conduct pain impulses from the receptors of the affected organ and the receptors of the corresponding skin area converge on the same neuron of the spinothalamic pathway. Irritation of this neuron from the receptors of the affected organ, in accordance with the law of pain projection, leads to the fact that pain is also felt in the area of ​​skin receptors.

Anti-pain (antinociceptive) system. In the second half of the twentieth century, data were obtained on the existence of a physiological system that limits the conduction and perception of pain sensitivity. Its important component is the “gate control” of the spinal cord. It is carried out in the posterior columns by inhibitory neurons, which, through presynaptic inhibition, limit the transmission of pain impulses along the spinothalamic pathway.

A number of brain structures exert a downward activating effect on the inhibitory neurons of the spinal cord. These include the central gray matter, the raphe nuclei, the locus coeruleus, the lateral reticular nucleus, the paraventricular and preoptic nuclei of the hypothalamus. The somatosensory area of ​​the cortex integrates and controls the activity of the structures of the analgesic system. Violation of this function can cause unbearable pain.

The most important role in the mechanisms of the analgesic function of the CNS is played by the endogenous opiate system (opiate receptors and endogenous stimulants).

Endogenous stimulants of opiate receptors are enkephalins and endorphins. Some hormones, such as corticoliberin, can stimulate their formation. Endorphins act mainly through morphine receptors, which are especially abundant in the brain: in the central gray matter, raphe nuclei, and the middle thalamus. Enkephalins act through receptors located predominantly in the spinal cord.

Theories of pain. There are three theories of pain:

1.intensity theory . According to this theory, pain is not a specific feeling and does not have its own special receptors, but arises under the action of superstrong stimuli on the receptors of the five sense organs. Convergence and summation of impulses in the spinal cord and brain are involved in the formation of pain.

2.Specificity theory . According to this theory, pain is a specific (sixth) sense that has its own receptor apparatus, afferent pathways and brain structures that process pain information.

3.Modern theory pain is based primarily on the theory of specificity. The existence of specific pain receptors has been proven.

At the same time, in the modern theory of pain, the position on the role of central summation and convergence in the mechanisms of pain is used. The most important achievement in the development of modern pain theory is the study of the mechanisms of the central perception of pain and the analgesic system of the body.

Functions of proprioreceptors

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

muscle spindles human, are elongated formations several millimeters long, tenths of a millimeter wide, which are located in the thickness of the muscle. In different skeletal muscles, the number of spindles per 1 g of tissue varies from a few to hundreds.

Thus, muscle spindles, as sensors of the state of muscle strength and the rate of its stretching, respond to two influences: peripheral - a change in muscle length, and central - a change in the level of activation of gamma motor neurons. Therefore, the reactions of the spindles in the conditions of natural muscle activity are quite complex. When a passive muscle is stretched, activation of spindle receptors is observed; it causes the myotatic reflex, or stretch reflex. With active muscle contraction, a decrease in its length has a deactivating effect on the spindle receptors, and excitation of gamma motor neurons, accompanying excitation of alpha motor neurons, leads to reactivation of the receptors. As a result, the impulse from the spindle receptors during movement depends on the length of the muscle, the speed of its shortening and the force of contraction.

Tendon organs (Golgi receptors) of a person are located in the area of ​​\u200b\u200bconnection of muscle fibers with a tendon, sequentially with respect to muscle fibers.

The tendon organs are an elongated spindle-shaped or cylindrical structure, the length of which in humans can reach 1 mm. This primary sensory receptor. At rest, i.e. when the muscle is not contracted, background impulses come from the tendon organ. Under conditions of muscle contraction, the impulse frequency increases in direct proportion to the magnitude of muscle contraction, which allows us to consider the tendon organ as a source of information about the force developed by the muscle. At the same time, the tendon organ reacts poorly to muscle stretching.

As a result of the sequential attachment of the tendon organs to the muscle fibers (and in some cases to the muscle spindles), the tendon mechanoreceptors are stretched when the muscles are tense. Thus, unlike muscle spindles, tendon receptors inform the nerve centers about the degree of tension in the mouse, and the rate of its development.

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

Conductor and cortical departments proprioceptive analyzer of mammals and humans. Information from muscle, tendon and joint receptors enters the spinal cord through the axons of the first afferent neurons located in the spinal ganglia, where it partially switches to alpha motor neurons or interneurons (for example, to Renshaw cells), and partially goes along ascending pathways to higher parts of the brain. In particular, along the Flexig and Gowers pathways, proprioceptive impulses are delivered to the cerebellum, and along the Gaulle and Burdach bundles, passing in the dorsal cords of the spinal cord, it reaches the neurons of the nuclei of the same name located in the medulla oblongata.

Axons of thalamic neurons (neurons of the third order) terminate in the cerebral cortex, mainly in the somatosensory cortex (postcentral gyrus) and in the region of the Sylvian sulcus (regions S-1 and S-2, respectively), and also partially in the motor ( prefrontal) area of ​​the cortex. This information is used by the motor systems of the brain quite widely, including for making a decision about the idea of ​​movement, as well as for its implementation. In addition, on the basis of proprioceptive information, a person forms ideas about the state of muscles and joints, as well as, in general, about the position of the body in space.

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

Thus, proprioceptive sensations enable a person to perceive changes in the position of individual parts of the body at rest and during movements. Information coming from proprioceptors allows him to constantly control the posture and accuracy of voluntary movements, dose the force of muscle contractions when counteracting external resistance, for example, when lifting or moving a load.

Sensory systems, their meaning and classification. Interaction of sensory systems.

To ensure the normal functioning of an organism*, the constancy of its internal environment, connection with the constantly changing external environment and adaptation to it are necessary. The body receives information about the state of the external and internal environments with the help of sensory systems that analyze (distinguish) this information, provide the formation of sensations and ideas, as well as specific forms of adaptive behavior.

The concept of sensory systems was formulated by I. P. Pavlov in the study 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. The concept of "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, there is still the concept of "sense organ" as a peripheral entity that perceives and partially analyzes environmental factors. The main part of the sense organ are receptors, equipped with auxiliary structures that provide optimal perception.

With the direct impact of various environmental factors with the participation of sensory systems in the body, there are Feel, which are reflections of the properties of objects of the objective world. The peculiarity of sensations is their modality, those. the totality of sensations provided by any one sensory system. Within each modality, according to the type (quality) of the sensory impression, different qualities can be distinguished, or valency. Modalities are, for example, sight, hearing, taste. Qualitative types of modality (valency) for vision are various colors, for taste - the sensation of sour, sweet, salty, bitter.

The activity of sensory systems is usually associated with the emergence of five senses - sight, hearing, taste, smell and touch, with the help of which the organism is connected with the external environment. However, in reality there are much more of them.

The classification of sensory systems can be based on various features: the nature of the acting stimulus, the nature of the sensations that arise, the level of sensitivity of receptors, the rate of adaptation, and much more.

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

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

Internal (visc

General information

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

Sensory organization of personality

The sensory organization of the personality is the level of development of individual systems of sensitivity and the possibility of their association. The sensory systems of a person are his sense organs, as if receivers of his sensations, in which sensation is transformed into perception.

Every 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 trait. For example, bats have developed sensitivity to the perception of short ultrasonic pulses, dogs have olfactory sensitivity.

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

What do we know about the world and about ourselves? Where do we get this knowledge from? 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 the 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 the phenomena of the external world is delivered to the brain. In the same way, a loop closes through sensations to receive feedback about the current physical and, to some extent, mental state of the organism.

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 takes place in human sensory systems, and already on its basis, cognitive processes that are more complex in their structure arise: perceptions, representations, memory, thinking.

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

Sensation Processing

After the information is received by the brain, the result of its processing is the development of a response or strategy aimed, for example, at improving physical tone, focusing more on current activities, or setting up for accelerated inclusion in mental activity.

Generally speaking, the response or strategy worked out at any given time is the best choice of the options available to the person at the time of the decision. However, it is clear that the number of options available and the quality of choice vary from person to person and depend on, for example:

mental properties of personality,

strategies for interacting with others

some of the physical condition,

experience, the availability of the necessary information in memory and the possibility of retrieving it.

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

For example, the baby went out naked in the cold, his skin feels cold, perhaps chills appear, he becomes uncomfortable, a signal about this enters the brain and a deafening roar is heard. The reaction to cold (stimulus) in an adult may be different, he will either rush to get dressed, or jump into a warm room, or try to warm himself in another way, for example, by running or jumping.

Improving the higher mental functions of the brain

Over time, children improve their reactions, multiplying the effectiveness of the result achieved. But after growing up, the opportunities for improvement do not disappear, despite the fact that the adult's susceptibility to them decreases. It is in this that "Effekton" sees part of its mission: increasing the efficiency of intellectual activity by training the higher mental functions of the brain.

Effekton's software products make it possible to measure various indicators of the human sensorimotor system (in particular, the Jaguar package contains tests of the time of a simple audio and visual-motor reaction, a complex visual-motor reaction, and the accuracy of perception of time intervals). Other packages of the "Effekton" complex evaluate the properties of cognitive processes of higher levels.

Therefore, it is necessary to develop the perception of the child, and the use of the package "Jaguar" can help you with this.

Physiology of sensations

Analyzers

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 conversion of external energy into a nervous process)

central part of the analyzer - afferent or sensory nerves

cortical sections of the analyzer, in which the processing of nerve impulses takes place.

Certain receptors correspond to their sections of cortical cells.

The specialization of each sense organ is based not only on the structural features of the receptor analyzers, but also on the specialization of the neurons that make up the central nervous apparatus, which receive signals perceived by the peripheral senses. The analyzer is not a passive receiver of energy; it is reflexively rebuilt under the influence of stimuli.

The movement of stimulus from the outer to the inner world

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

the stimulus causes certain changes in energy 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 brain and sensory systems of a person, but also on the characteristics of the person himself, his development and condition. With illness or fatigue, a person changes sensitivity to certain influences.

There are also cases of pathologies when a person is deprived, for example, of hearing or sight. If this trouble is congenital, then there is a violation of the flow of information, which can lead to mental retardation. If these children were taught special techniques to compensate for their shortcomings, 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 value of the stimulus at which a sensation appears is the absolute threshold of sensation. The value of this threshold characterizes the absolute sensitivity, which is numerically equal to the value inversely proportional to the absolute threshold of sensations. And sensitivity to a change in the stimulus is called relative or difference sensitivity. The minimum difference between two stimuli, which causes a slightly noticeable difference in sensations, is called the difference threshold.

Based on this, we can conclude that it is possible to measure sensations. And once again you come to admiration from amazing delicately working devices - human sense organs or human sensory systems.

Effekton's software products make it possible to measure various indicators of the human sensory system (for example, the Jaguar package contains tests of the speeds of a simple audio and visual-motor reaction, a complex visual-motor reaction, the accuracy of time perception, the accuracy of space perception, and many others). Other packages of the "Effekton" complex also evaluate the properties of cognitive processes of higher levels.

Classification of sensations

Five basic types of sensations: sight, hearing, touch, smell and taste - were already known to the ancient Greeks. At present, 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.

Sensations are classified 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 arise in the presence or absence of direct contact of the receptor with the stimulus. Sight, hearing, smell are distant sensations. These types of sensations provide orientation in the nearest environment. Taste, pain, tactile sensations - contact.

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

exteroception - visual, auditory, tactile and others;

proprioception - sensations from muscles, tendons;

interoception - feelings of hunger, thirst.

In the course of the evolution of all living things, sensitivity has undergone changes from the most ancient to the modern. So, distant sensations can be considered more modern than contact ones, but in the structure of the contact analyzers themselves, one can also reveal more ancient and completely new functions. So, for example, pain sensitivity is more ancient than tactile.

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

Types of sensations

Vision, hearing

Let us consider various types of sensations, bearing in mind that vision and hearing are the most well studied.

All sensory systems are built according to a single principle and consist of three sections: peripheral, conductive and central.

Peripheral department represented by the sense organ. It consists of receptors - the endings of sensitive nerve fibers or specialized cells. They provide the conversion of stimulus energy into nerve impulses.

Receptors differ in location (internal and external), structure and characteristics of the perception of stimulus energy (some perceive mechanical, others - chemical, and others - light stimuli).

In addition to receptors, the sense organs include auxiliary structures that perform protective, support, and some other functions. For example, the auxiliary apparatus of the eye is represented by the oculomotor muscles, eyelids and lacrimal glands.

The conductive section of the sensory system consists of sensory nerve fibers, which in most cases form a specialized nerve. It delivers information from receptors to the central part of the sensory system.

And finally, the central section is located in the cerebral cortex. Here are the higher sensory centers that provide the final analysis of the information received and the formation of appropriate sensations.

Thus, the sensory system is a set of specialized structures of the nervous system that carry out the processes of receiving and processing information from the external and internal environment, and also form sensations.

There are visual, auditory, vestibular, gustatory, olfactory and other sensory systems.

visual sensory system

Its peripheral part is represented by the organ of vision (eye), the conductive part is represented by the optic nerve, and the central part is represented by the visual zone located in the occipital lobe of the cerebral cortex.

Light rays from the objects under consideration act on the light-sensitive cells of the eye and cause excitation in them. It is transmitted along the optic nerve to the cerebral cortex. Here in the occipital lobes there are visual sensations of the shape, color, size, location and direction of movement of objects.

auditory sensory system plays a very important role. Her work is at the heart of teaching speech. It is represented by the ear - the organ of hearing (peripheral section), the auditory nerve (conductor section) and the auditory zone located in the temporal lobe of the cerebral cortex (central section).

vestibular sensory system provides spatial orientation of a person. With its help, we obtain information about the accelerations and decelerations that occur during movement. It is represented by the organ of balance, the vestibular nerve and the corresponding zone in the temporal lobes of the cerebral cortex.

A sense of the position of the body in space is especially necessary for pilots, scuba divers, acrobats, etc. If the balance organ is damaged, a person cannot stand and walk confidently.

Taste sensory system analyzes soluble chemical irritants acting on the organ of taste (tongue). With its help, the suitability of food is determined.

Our tongue is covered with a mucous membrane, the folds of which contain taste buds (Fig.). Inside each kidney are receptor cells with microvilli.

Receptors are associated with nerve fibers that enter the brain as part of the cranial nerves. Through them, impulses reach the back of the central gyrus of the cerebral cortex, where taste sensations are formed.

There are four basic taste sensations: bitter, sweet, sour and salty. The tip of the tongue is most sensitive to sweet, the edges to salt and sour, and the root to bitter substances.

Olfactory sensory system carries out the perception and analysis of chemical stimuli in the external environment.

The peripheral part of the olfactory sensory system is represented by the epithelium of the nasal cavity, which contains receptor cells with microvilli. The axons of these sensory cells form the olfactory nerve, which goes into the cranial cavity (Fig.).

Through it, excitation is conducted to the olfactory centers of the cerebral cortex, where odor recognition is carried out.

Touch plays an essential role in the knowledge of the external world. It provides the ability to perceive and distinguish the shape, size and nature of the surface of an object. The receptors involved in the processes of perception of stimuli acting on the skin are very diverse. They react not only to touch, but also to heat, cold and pain. Most of all tactile receptors are on the lips and the palmar surface of the fingers, the least of all - on the torso. Excitation from receptors is transmitted through sensitive neurons to the zone of skin sensitivity of the cerebral cortex, where the corresponding sensations arise.