Sensory system organs and functions. Human sensory systems (analyzers)

sensory systems- these are specialized parts of the nervous system, including peripheral receptors (sensory organs, or sense organs), nerve fibers extending from them (pathways) and cells of the central nervous system grouped together (sensory centers). Each area of the brain that contains sensory center (nucleus) and the switching of nerve fibers occurs, forms level sensory system. In the sensory organs, the energy of an external stimulus is converted into a nerve signal - reception Nerve signal (receptor potential) transforms into impulse activity or action potentials neurons (coding). Along the pathways, action potentials reach the sensory nuclei, on the cells of which nerve fibers are switched and the nerve signal is converted (recoding). At all levels of the sensory system, simultaneously with the coding and analysis of stimuli, decoding signals, i.e. reading touch code. Decoding is carried out on the basis of connections between sensory nuclei and motor and associative parts of the brain. Nerve impulses from the axons of sensory neurons in the cells of the motor systems cause excitation (or inhibition). The result of these processes is movement- action or stop of movement - inaction. The final manifestation of the activation of associative functions is also movement.

The main functions of sensor systems are:

signal reception;
conversion of receptor potential into impulse activity of nerve pathways;
transmission of neural activity to sensory nuclei;
transformation of neural activity in sensory nuclei at each level;
analysis of signal properties;
identification of signal properties;
classification and identification of a signal (decision making).

12. Definition, properties and types of receptors.

Receptors are special cells or special nerve endings designed to transform energy (convert) various types of stimuli into specific activity of the nervous system (into a nerve impulse).

Signals entering the central nervous system from receptors cause either new reactions or change the course of activity currently occurring.

Most receptors are represented by a cell equipped with hairs or cilia, which are structures that act like amplifiers in relation to stimuli.

Either mechanical or biochemical interaction of the stimulus with the receptors occurs. The stimulus perception thresholds are very low.

According to the action of stimuli, receptors are divided:

1. Interoreceptors

2. Exteroceptors

3. Proprioceptors: muscle spindles and Golgi tendon organs (I.M. Sechenov discovered a new type of sensitivity - joint-muscular feeling).

There are 3 types of receptors:

1. Phasic - these are receptors that are excited during the initial and final periods of the stimulus.

2. Tonic - act during the entire period of action of the stimulus.

3. Phaso-tonic - in which impulses occur all the time, but more at the beginning and at the end.

The quality of perceived energy is called modality.

Receptors can be:

1. Monomodal (perceive 1 type of stimulus).

2. Polymodal (can perceive several stimuli).

The transmission of information from peripheral organs occurs along sensory pathways, which can be specific and nonspecific.

Specific are monomodal.

Nonspecific are multimodal

Properties

Selectivity - sensitivity to adequate stimuli

· Excitability - the minimum amount of energy of an adequate stimulus, which is necessary for the occurrence of excitation, i.e. threshold of excitation.

Low thresholds for adequate stimuli

· Adaptation (can be accompanied by both a decrease and an increase in the excitability of receptors. Thus, when moving from a light room to a dark one, a gradual increase in the excitability of the photoreceptors of the eye occurs, and a person begins to distinguish dimly lit objects - this is the so-called dark adaptation.)

13. Mechanisms of excitation of primary sensory and secondary sensory receptors.

Primary sensory receptors: the stimulus acts on the dendrite of the sensory neuron, the permeability of the cell membrane to ions (mainly Na+) changes, a local electrical potential (receptor potential) is formed, which electrotonically propagates along the membrane to the axon. An action potential is formed on the axon membrane, which is transmitted further to the central nervous system.

A sensory neuron with a primary sensory receptor is a bipolar neuron, at one pole of which there is a dendrite with a cilium, and at the other there is an axon that transmits excitation to the central nervous system. Examples: proprioceptors, thermoreceptors, olfactory cells.

Secondary sensory receptors: in them, the stimulus acts on the receptor cell, and excitation occurs in it (receptor potential). On the axon membrane, the receptor potential activates the release of a neurotransmitter into the synapse, as a result of which a generator potential is formed on the postsynaptic membrane of the second neuron (most often bipolar), which leads to the formation of an action potential in neighboring areas of the postsynaptic membrane. This action potential is then transmitted to the central nervous system. Examples: ear hair cells, taste buds, eye photoreceptors.

!14. Organs of smell and taste (localization of receptors, first switching, repeated switching, projection zone).

The organs of smell and taste are stimulated by chemical stimuli. The receptors of the olfactory analyzer are excited by gaseous substances, and the taste receptors - by dissolved chemicals. The development of the olfactory organs also depends on the lifestyle of animals. The olfactory epithelium is located away from the main respiratory tract and the inhaled air enters there by vortex movements or diffusion. Such vortex movements occur during “sniffing”, i.e. with short breaths through the nose and widening of the nostrils, which makes it easier for the analyzed air to penetrate these areas.

Olfactory cells are represented by bipolar neurons, the axons of which form the olfactory nerve, ending in the olfactory bulb, which is the olfactory center, and then from it there are paths to other overlying brain structures. On the surface of the olfactory cells there are a large number of cilia, which significantly increase the olfactory surface.

Taste analyzer serves to determine the nature, taste of food, and its suitability for eating. For animals living in water, taste and olfactory analyzers help navigate the environment, determine the presence of food, and females. With the transition to life in the air, the importance of the taste analyzer decreases. In herbivorous animals, the taste analyzer is well developed, which can be seen in the pasture and in the feeder, when the animals do not eat all the grass and hay.

The peripheral section of the taste analyzer is represented by taste buds located on the tongue, soft palate, posterior wall of the pharynx, tonsils and epiglottis. Taste buds are located on the surface of the fungiform, foliate and circumvallate papillae

15. Skin analyzer (localization of receptors, first switching, repeated switching, projection zone).

Various receptor formations are located in the skin. The simplest type of sensory receptor is the free nerve ending. Morphologically differentiated formations have a more complex organization, such as tactile discs (Merkel discs), tactile corpuscles (Meissner corpuscles), lamellar corpuscles (Pacini corpuscles) - pressure and vibration receptors, Krause flasks, Ruffini corpuscles, etc.

Most specialized terminal structures are characterized by preferential sensitivity to certain types of irritation, and only free nerve endings are multimodal receptors.

16. Visual analyzer (localization of receptors, first switching, repeated switching, projection zone).

A person receives the largest amount of information (up to 90%) about the outside world through the organ of vision. The organ of vision - the eye - consists of the eyeball and an auxiliary apparatus. The auxiliary apparatus includes the eyelids, eyelashes, lacrimal glands and muscles of the eyeball. The eyelids are formed by folds of skin lined from the inside with a mucous membrane - the conjunctiva. The lacrimal glands are located in the outer upper corner of the eye. Tears wash the anterior part of the eyeball and enter the nasal cavity through the nasolacrimal duct. The muscles of the eyeball set it in motion and direct it towards the object in question.
17. Visual analyzer. The structure of the retina. Formation of color perception. Wiring department. Information processing .

The retina has a very complex structure. It contains light-receiving cells - rods and cones. Rods (130 million) are more sensitive to light. They are called twilight vision apparatus. Cones (7 million) are the apparatus for daytime and color vision. When these cells are irritated by light rays, excitation occurs, which is carried through the optic nerve to the visual centers located in the occipital zone of the cerebral cortex. The area of the retina from which the optic nerve emerges is devoid of rods and cones and is therefore incapable of perceiving light. It is called a blind spot. Almost next to it is a yellow spot formed by a cluster of cones - the place of best vision.

The optical, or refractive, system of the eye includes: the cornea, aqueous humor, lens and vitreous body. In people with normal vision, rays of light passing through each of these media are refracted and then hit the retina, where they form a reduced and inverted image of objects visible to the eye. Of these transparent media, only the lens is capable of actively changing its curvature, increasing it when viewing close objects and decreasing it when looking at distant objects. This ability of the eye to clearly see objects at different distances is called accommodation. If rays are refracted too strongly when passing through transparent media, they are focused in front of the retina, resulting in myopia. In such people, the eyeball is either elongated or the curvature of the lens is increased. The weak refraction of these media causes the rays to focus behind the retina, causing farsightedness. It occurs due to shortening of the eyeball or flattening of the lens. Properly selected glasses can correct these Conducting paths of the visual analyzer. First, the second and third neurons of the visual analyzer pathway are located in the retina. The fibers of the third (ganglionic) neurons in the optic nerve partially intersect to form the optic chiasm. After the chiasm, the right and left visual tracts are formed. The fibers of the optic tract end in the diencephalon (nucleus of the lateral geniculate body and the thalamic cushion), where the fourth neurons of the optic tract are located. A small number of fibers reach the midbrain in the area of the superior colliculus. The axons of the fourth neurons pass through the posterior leg of the internal capsule and are projected onto the cortex of the occipital lobe of the cerebral hemispheres, where the cortical center of the visual analyzer is located. visual impairments.

18. Auditory analyzer (localization of receptors, first switching, repeated switching, projection zone). Wiring department. Processing information. Auditory adaptation.

Auditory and vestibular analyzers. The organ of hearing and balance includes three sections: the outer, middle and inner ear. The outer ear consists of the pinna and the external auditory canal. The auricle is made of elastic cartilage covered with skin and serves to capture sound. The external auditory canal is a 3.5 cm long canal that begins with the external auditory opening and ends blindly with the tympanic membrane. It is lined with skin and has glands that secrete earwax.

Behind the eardrum is the middle ear cavity, which consists of the air-filled tympanic cavity, the auditory ossicles and the auditory (Eustachian) tube. The auditory tube connects the tympanic cavity with the cavity of the nasopharynx, which helps equalize the pressure on both sides of the eardrum. The auditory ossicles - the hammer, incus and stirrup - are movably connected to each other. The hammer is fused with the handle to the eardrum; the head of the malleus is adjacent to the anvil, which at the other end is connected to the stapes. The stapes is connected with a wide base to the membrane of the oval window leading to the inner ear. The inner ear is located in the thickness of the pyramid of the temporal bone; consists of a bony labyrinth and a membranous labyrinth located in it. The space between them is filled with fluid - perilymph, the cavity of the membranous labyrinth - endolymph. The bony labyrinth contains three sections: the vestibule, the cochlea and the semicircular canals. The cochlea belongs to the organ of hearing, the rest of its parts belong to the organ of balance.

The cochlea is a bone canal twisted in the form of a spiral. Its cavity is divided by a thin membranous septum - the main membrane. It consists of numerous (about 24 thousand) connective tissue fibers of different lengths. The receptor hair cells of the organ of Corti, the peripheral part of the auditory analyzer, are located on the main membrane.

Sound waves through the external auditory canal reach the eardrum and cause its vibrations, which are amplified (almost 50 times) by the auditory ossicle system and transmitted to the perilymph and endolymph, then perceived by the fibers of the main membrane. High sounds cause vibrations of short fibers, low sounds cause vibrations of longer ones located at the top of the cochlea. These vibrations excite the receptor hair cells of the organ of Corti. Next, the excitation is transmitted along the auditory nerve to the temporal lobe of the cerebral cortex, where the final analysis and synthesis of sound signals occurs. The human ear perceives sounds with a frequency of 16 to 20 thousand Hz.

Conducting paths of the auditory analyzer. First neuron of the auditory analyzer pathways - the above-mentioned bipolar cells. Their axons form the cochlear nerve, the fibers of which enter the medulla oblongata and end in the nuclei where the cells of the second neuron of the pathways are located. The axons of the cells of the second neuron reach the internal geniculate body, mainly the opposite side. The third neuron begins here, along which impulses reach the auditory area of the cerebral cortex.

In addition to the main conducting path connecting the peripheral part of the auditory analyzer with its central, cortical part, there are other paths through which reflex reactions to irritation of the organ of hearing in an animal can be carried out even after the removal of the cerebral hemispheres. Indicative reactions to sound are of particular importance. They are carried out with the participation of the quadrigeminal, to the posterior and partly anterior tubercles of which there are collaterals of fibers directed to the internal geniculate body.

19. Vestibular analyzer (localization of receptors, first switching, repeated switching, projection zone). Wiring department. Information processing .

Vestibular apparatus. It is represented by the vestibule and semicircular canals and is an organ of balance. In the vestibule there are two sacs filled with endolymph. At the bottom and in the inner wall of the sacs there are receptor hair cells, which are adjacent to the otolithic membrane with special crystals - otoliths containing calcium ions. The three semicircular canals are located in three mutually perpendicular planes. The bases of the canals at the points of their connection with the vestibule form extensions - ampoules in which hair cells are located.

Receptors of the otolithic apparatus are excited by accelerating or decelerating rectilinear movements. The receptors of the semicircular canals are irritated by accelerated or slowed rotational movements due to the movement of endolymph. Excitation of the receptors of the vestibular apparatus is accompanied by a number of reflex reactions: changes in muscle tone that promote straightening of the body and maintaining posture. Impulses from the receptors of the vestibular apparatus travel along the vestibular nerve to the central nervous system. The vestibular analyzer is connected to the cerebellum, which regulates its activity.

Conducting pathways of the vestibular apparatus. Conducting the path of the statokinetic apparatus transmits impulses when the position of the head and body changes, participating together with other analyzers in the body’s orienting reactions relative to the surrounding space. The first neuron of the statokinetic apparatus is located in the vestibular ganglion, which lies at the bottom of the internal auditory canal. The dendrites of the bipolar cells of the vestibular ganglion form the vestibular nerve, formed by 6 branches: superior, inferior, lateral and posterior ampullary, utricular and saccular. They contact the sensitive cells of the auditory maculae and scallops located in the ampoules of the semicircular canals, in the sac and uterus of the vestibule of the membranous labyrinth.

20. Vestibular analyzer. Formation of a sense of balance. Automatic and conscious control of body balance. Participation of the vestibular apparatus in the regulation of reflexes .

The vestibular apparatus performs the functions of perceiving the position of the body in space and maintaining balance. With any change in the position of the head, the receptors of the vestibular apparatus are irritated. The impulses are transmitted to the brain, from which nerve impulses are sent to the skeletal muscles to correct body position and movements. The vestibular apparatus consists of two parts: vestibule and semicircular canals, in which the receptors of the statokinetic analyzer are located.

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

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

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

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

· central section of the analyzer- afferent or sensory nerves

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

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

Classification of sensations

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

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

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

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

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

Bounds method

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

Installation method

the subject independently distinguishes the magnitude of the stimulus

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1. SENSORY SYSTEMS

1.1 General understanding of sensory systems

Sensory - from the Latin sensus - feeling, sensation.

The sensory system is an integral nervous mechanism that receives and analyzes sensory information. A synonym for the sensory system in Russian psychology is the term “analyzer,” which was first introduced by the outstanding Russian physiologist I.P. Pavlov.

The analyzer consists of three parts:

1) peripheral department - a receptor that receives and transforms external energy into a nervous process, and an effector - an organ or system of organs that responds to the actions of external or internal stimuli, acting as the executive element of the reflex act; sensory visual sensitivity sensitization

2) conducting pathways - afferent (ascending) and efferent (descending), connecting the peripheral part of the analyzer with the central one;

3) the central section - represented by the subcortical and cortical nuclei and projection sections of the cerebral cortex, where the processing of nerve impulses coming from the peripheral sections occurs.

Each analyzer has a core, i.e. the central part, where the bulk of the receptor cells is concentrated, and the periphery, consisting of scattered cellular elements, which are located in varying quantities in various areas of the cortex. The nuclear part of the analyzer consists of a large mass of cells that are located in the area of the cerebral cortex where the centripetal nerves from the receptor enter. The scattered (peripheral) elements of this analyzer are included in areas adjacent to the cores of other analyzers. This ensures the participation of a large part of the entire cerebral cortex in a separate sensory act. The analyzer core performs the function of fine analysis and synthesis, for example, it differentiates sounds by height. Scattered elements are associated with the function of coarse analysis, for example, distinguishing between musical sounds and noise.

Certain cells of the peripheral parts of the analyzer correspond to certain areas of cortical cells. Thus, spatially different points in the cortex represent, for example, different points of the retina; The spatially different arrangement of cells is represented in the cortex and the organ of hearing. The same applies to other senses.

Numerous experiments carried out using artificial stimulation methods now make it possible to quite definitely establish the localization in the cortex of certain types of sensitivity. Thus, the representation of visual sensitivity is concentrated mainly in the occipital lobes of the cerebral cortex. Auditory sensitivity is localized in the middle part of the superior temporal gyrus. Touch-motor sensitivity is represented in the posterior central gyrus, etc.

For the sensory process to occur, the entire analyzer as a whole must work. The impact of an irritant on the receptor causes irritation. The beginning of this irritation is the transformation of external energy into a nervous process, which is produced by the receptor. From the receptor, this process reaches the nuclear part of the analyzer along ascending pathways. When excitation reaches the cortical cells of the analyzer, the body's response to irritation occurs. We perceive light, sound, taste or other qualities of stimuli.

Thus, the analyzer constitutes the initial and most important part of the entire path of nervous processes, or reflex arc. The reflex arc consists of a receptor, pathways, a central part and an effector. The interconnection of the elements of the reflex arc provides the basis for the orientation of a complex organism in the surrounding world, the activity of the organism depending on the conditions of its existence.

1.2 Types of sensory systems

For a long time, visual, auditory, tactile, olfactory and gustatory sensitivity was considered to be the basis on which the entire mental life of a person is built with the help of associations. In the 19th century, this list began to expand rapidly. Sensitivity to the position and movement of the body in space was added to it, vestibular sensitivity, tactile sensitivity, etc. were discovered and studied.

The first classification was put forward by Aristotle, who lived in 384-322. BC, who identified 5 types of “external senses”: visual, auditory, olfactory, tactile, gustatory.

The German physiologist and psychophysicist Ernst Weber (1795-1878) expanded the Aristotelian classification, proposing to divide the sense of touch into: the sense of touch, the sense of weight, the sense of temperature.

In addition, he identified a special group of feelings: the feeling of pain, the sense of balance, the sense of movement, the sense of internal organs.

The classification of the German physicist, physiologist, psychologist Hermann Helmholtz (1821-1894) is based on the categories of modality; in fact, this classification is also an extension of Aristotle’s classification. Since modalities are distinguished by the corresponding sense organs, for example, sensory processes associated with the eye belong to the visual modality; sensory processes associated with hearing - to the auditory modality, etc. In a modern modification of this classification, the additional concept of submodality is used, for example, in a modality such as skin feeling, submodalities are distinguished: mechanical, temperature and pain. Similarly, within the visual modality, achromatic and chromatic submodalities are distinguished.

German psychologist, physiologist, philosopher Wilhelm Wundt (1832-1920) is considered the founder of the classification of sensory systems based on the type of energy of an adequate stimulus for the corresponding receptors: physical (vision, hearing); mechanical (touch); chemical (taste, smell).

This idea was not widely developed, although it was used by I.P. Pavlov to develop the principles of physiological classification.

The classification of sensations by the outstanding Russian physiologist Ivan Petrovich Pavlov (1849-1936) is based on the physicochemical characteristics of stimuli. To determine the quality of each analyzer, he used the physicochemical characteristics of the signal. Hence the names of the analyzers: light, sound, skin-mechanical, olfactory, etc., and not visual, auditory, etc., as analyzers were usually classified.

The classifications discussed above did not allow us to reflect the multi-level nature of different types of receptions, some of which are earlier and lower in level of development, while others are later and more differentiated. Ideas about the multi-level affiliation of certain sensory systems are associated with the model of human skin receptions developed by G. Head.

The English neurologist and physiologist Henry Head (1861-1940) proposed a genetic classification principle in 1920. He distinguished between protopathic sensitivity (lower) and epicritic sensitivity (highest).

Tactile sensitivity was identified as epicritic, or discriminative, sensitivity of the highest level; and protopathic sensitivity, archaic, lower level - painful. He proved that protopathic and epicritic components can be both inherent in different modalities and occur within one modality. Younger and more advanced epicritic sensitivity allows you to accurately localize an object in space, it provides objective information about the phenomenon. For example, touch allows you to accurately determine the location of a touch, and hearing allows you to determine the direction in which the sound was heard. Relatively ancient and primitive sensations do not provide precise localization either in external space or in the space of the body. For example, organic sensitivity - a feeling of hunger, a feeling of thirst, etc. They are characterized by constant affective overtones, and they reflect subjective states rather than objective processes. The ratio of protopathic and epicritic components in different types of sensitivity turns out to be different.

Alexey Alekseevich Ukhtomsky (1875-1942), an outstanding Russian physiologist, one of the founders of the physiological school of St. Petersburg University, also used the genetic principle of classification. The highest receptions according to Ukhtomsky are hearing and vision, which are in constant interaction with the lower ones, thanks to which they improve and develop. For example, the genesis of visual reception lies in the fact that first tactile reception turns into tactile-visual, and then into purely visual reception.

The English physiologist Charles Sherrington (1861-1952) in 1906 developed a classification that takes into account the location of the receptive surfaces and the function they perform:

1. Exteroception (external reception): a) contact; b) distant; c) contact-distant;

2. Proprioception (reception in muscles, ligaments, etc.): a) static; b) kinesthetic.

3. Interoception (reception of internal organs).

Charles Sherrington's systemic classification divided all sensory systems into three main blocks.

The first block is exteroception, which brings to a person information coming from the outside world and is the main reception that connects a person with the outside world. It includes: vision, hearing, touch, smell, taste. All exteroception is divided into three subgroups: contact, distant and contact-distant.

Contact exteroception occurs when a stimulus is applied directly to the surface of the body or the corresponding receptors. Typical examples include sensory acts of touch and pressure, touch, and taste.

Distant exteroception occurs without direct contact of the stimulus with the receptor. In this case, the source of irritation is located at some distance from the receptive surface of the corresponding sensory organ. This includes vision, hearing, and smell.

Contact-distant exteroception is carried out both in direct contact with the stimulus and remotely. This includes temperature, skin and pain. vibratory sensory acts.

The second block is proprioception, which conveys to a person information about the position of his body in space and the state of his musculoskeletal system. All proprioception is divided into two subgroups: static and kinesthetic reception.

Static reception signals the position of the body in space and balance. Receptor surfaces that report changes in body position in space are located in the semicircular canals of the inner ear.

Kinesthetic reception signals the state of movement (kinesthesia) of individual parts of the body relative to each other, and the positions of the musculoskeletal system. Receptors for kinesthetic, or deep, sensitivity are located in muscles and articular surfaces (tendons, ligaments). Excitations that occur when muscles are stretched or joints change position cause kinesthetic reception.

The third block includes interoception, signaling the state of a person’s internal organs. These receptors are located in the walls of the stomach, intestines, heart, blood vessels and other visceral formations. Interoceptive are the feelings of hunger, thirst, sexual sensations, feelings of malaise, etc.

Modern authors use Aristotle's expanded classification, distinguishing between reception: touch and pressure, touch, temperature, pain, taste, olfactory, visual, auditory, position and movement (static and kinesthetic) and organic (hunger, thirst, sexual sensations, pain, internal sensations). organs, etc.), structuring it with the classification of Ch. Sherrington. The levels of organization of sensory systems are based on the genetic principle of G. Head's classification.

1.3 Chuvalidity of sensory systems

Sensitivity - the ability of the sense organs to respond to the appearance of a stimulus or its change, i.e. the ability for mental reflection in the form of a sensory act.

There are absolute and differential sensitivity. Absolute sensitivity - the ability to perceive stimuli of minimal strength (detection). Differential sensitivity is the ability to perceive a change in a stimulus or distinguish between similar stimuli within the same modality.

Sensitivity is measured or determined by the strength of the stimulus, which under given conditions is capable of causing sensation. Sensation is an active mental process partial reflections of objects or phenomena of the surrounding world, as well as internal states of the body, in the human mind under the direct influence of stimuli on the senses.

The minimum strength of the stimulus that can cause sensation is determined by the lower absolute threshold of sensation. Stimuli of lesser strength are called subthreshold. The lower threshold of sensations determines the level of absolute sensitivity of this analyzer. The lower the threshold value, the higher the sensitivity.

where E is sensitivity, P is the threshold value of the stimulus.

The value of the absolute threshold depends on age, the nature of the activity, the functional state of the body, the strength and duration of the current stimulus.

The upper absolute threshold of sensation is determined by the maximum strength of the stimulus, which also causes a sensation characteristic of a given modality. There are suprathreshold stimuli. They cause pain and destruction of the receptors of the analyzers, which are affected by suprathreshold stimulation. The minimum difference between two stimuli that causes different sensations in the same modality determines the difference threshold, or discrimination threshold. Difference sensitivity is inversely proportional to the discrimination threshold.

The French physicist P. Bouguer in 1729 came to the conclusion that the difference threshold of visual perception is directly proportional to its initial level. 100 years after P. Bouguer, the German physiologist Ernst Weber established that this pattern is also characteristic of other modalities. Thus, a very important psychophysical law was found, which was called the Bouguer-Weber law.

Bouguer-Weber law:

where?I is the difference threshold, I is the original stimulus.

The ratio of the difference threshold to the value of the original stimulus is a constant value and is called relative difference or differential threshold.

According to the Bouguer-Weber law, the differential threshold is a certain constant part of the value of the original stimulus by which it must be increased or decreased in order to obtain a barely noticeable change in sensation. The magnitude of the differential threshold depends on the modality of sensation. For vision it is approximately 1/100, for hearing 1/10, for kinesthesia 1/30, etc.

The reciprocal of the differential threshold is called differential sensitivity. Subsequent studies showed that the law is valid only for the middle part of the dynamic range of the sensor system, where differential sensitivity is maximum. The limits of this zone vary for different sensory systems. Outside this zone, the differential threshold increases, sometimes very significantly, especially when approaching the absolute lower or upper threshold.

The German physicist, psychologist and philosopher Gustav Fechner (1801-1887), the founder of psychophysics as the science of the natural connection between physical and mental phenomena, using a number of psychophysical laws found by that time, including the Bouguer-Weber law, formulated the following law.

Fechner's Law:

where S is the intensity of sensation, i is the strength of the stimulus, K is the Bouguer-Weber constant.

The intensity of sensations is proportional to the logarithm of the strength of the active stimulus, that is, the sensation changes much more slowly than the strength of irritation increases.

As signal intensity increases, an increasingly large difference between intensity units (i) is required to keep the differences between the sensation units (S) equal. In other words, while the sensation increases uniformly (in an arithmetic progression), the corresponding increase in signal intensity occurs physically unevenly, but proportionally (in a geometric progression). The relationship between quantities, one of which changes in an arithmetic progression, and the second in a geometric progression, is expressed by a logarithmic function.

Fechner's law is called the basic psychophysical law in psychology.

Stevens' law (power law) is a variant of the basic psychophysical law proposed by the American psychologist Stanley Stevens (1906-1973), which establishes a power-law rather than a logarithmic relationship between the intensity of sensation and the strength of stimuli:

where S is the intensity of the sensation, i is the strength of the stimulus, k is a constant depending on the unit of measurement, n is the exponent of the function. The exponent n of the power function is different for sensations of different modalities: the limits of its variation are from 0.3 (for sound volume) to 3.5 (for the strength of an electric shock).

The difficulty of detecting thresholds and recording changes in the intensity of sensation is the object of research at the present time. Modern researchers studying the detection of signals by various operators have come to the conclusion that the complexity of this sensory action lies not simply in the inability to perceive the signal due to its weakness, but in the fact that it is always present against the background of interference or “noise” masking it " The sources of this “noise” are numerous. Among them are extraneous stimuli, spontaneous activity of receptors and neurons in the central nervous system, changes in the orientation of the receptor relative to the stimulus, fluctuations in attention and other subjective factors. The action of all these factors leads to the fact that the subject often cannot say with complete confidence when the signal was presented and when it was not. As a result, the signal detection process itself becomes probabilistic. This feature of the occurrence of sensations of near-threshold intensity is taken into account in a number of recently created mathematical models that describe this sensory activity.

1.4 Variability of sensitivity

The sensitivity of analyzers, determined by the magnitude of absolute and difference thresholds, is not constant and can change. This variability in sensitivity depends both on environmental conditions and on a number of internal physiological and psychological conditions. There are two main forms of changes in sensitivity:

1) sensory adaptation - a change in sensitivity under the influence of the external environment;

2) sensitization - a change in sensitivity under the influence of the internal environment of the body.

Sensory adaptation - adaptation of the body to the actions of the environment due to changes in sensitivity under the influence of an active stimulus. There are three types of adaptation:

1. Adaptation as the complete disappearance of sensation during the prolonged action of a stimulus. In the case of constant stimuli, the sensation tends to fade. For example, clothes, a watch on your hand, soon cease to be felt. A common fact is the distinct disappearance of olfactory sensations soon after we enter an atmosphere with any persistent odor. The intensity of the taste sensation weakens if the corresponding substance is kept in the mouth for some time.

And finally, the sensation may fade away completely, which is associated with a gradual increase in the lower absolute threshold of sensitivity to the intensity level of a constantly acting stimulus. The phenomenon is typical for all modalities except visual.

Full adaptation of the visual analyzer under the influence of a constant and motionless stimulus does not occur under normal conditions. This is explained by compensation for the constant stimulus due to movements of the receptor apparatus itself. Constant voluntary and involuntary eye movements ensure continuity of visual sensation. Experiments in which conditions were artificially created to stabilize the image relative to the retina of the eyes showed that in this case the visual sensation disappears 2-3 seconds after its occurrence.

2. Adaptation as a dulling of sensation under the influence of a strong stimulus. A sharp decrease in sensation followed by recovery is a protective adaptation.

So, for example, when we find ourselves from a dimly lit room into a brightly lit space, we are first blinded and unable to discern any details around us. After some time, the sensitivity of the visual analyzer is restored, and we begin to see normally. The same thing happens when we find ourselves in a weaving workshop and at first, apart from the roar of the machines, we cannot perceive speech and other sounds. After some time, the ability to hear speech and other sounds is restored. This is explained by a sharp increase in the lower absolute threshold and the discrimination threshold with the subsequent restoration of these thresholds in accordance with the intensity of the current stimulus.

Types of adaptation described 1 and 2 can be combined under the general term “negative adaptation,” since their result is a general decrease in sensitivity. But “negative adaptation” is not a “bad” adaptation, since it is an adaptation to the intensity of existing stimuli and helps prevent the destruction of sensory systems.

3. Adaptation as an increase in sensitivity under the influence of a weak stimulus (decrease in the lower absolute threshold). This type of adaptation, characteristic of certain types of sensations, can be defined as positive adaptation.

In the visual analyzer, this is a dark adaptation, when the sensitivity of the eye increases under the influence of being in the dark. A similar form of auditory adaptation is adaptation to silence. In temperature sensations, positive adaptation is detected when a pre-cooled hand feels warm, and a pre-heated hand feels cold when immersed in water of the same temperature.

Studies have shown that some analyzers detect fast adaptation, while others detect slow adaptation. For example, tactile receptors adapt very quickly. The visual receptor adapts relatively slowly (dark adaptation time reaches several tens of minutes), olfactory and gustatory.

The phenomenon of adaptation can be explained by those peripheral changes that occur in the functioning of the receptor under the influence of direct and feedback from the analyzer core.

Adaptive regulation of the level of sensitivity depending on what stimuli (weak or strong) affects the receptors is of great biological importance. Adaptation helps the sensory organs to detect weak stimuli and protects the sensory organs from excessive irritation in the event of unusually strong influences.

So, adaptation is one of the most important types of changes in sensitivity, indicating the greater plasticity of the organism in its adaptation to environmental conditions.

Another type of change in sensitivity is sensitization. The process of sensitization differs from the process of adaptation in that during the adaptation process sensitivity changes in both directions - that is, it increases or decreases, but in the process of sensitization - only in one direction, namely, increasing sensitivity. In addition, changes in sensitivity during adaptation depend on environmental conditions, and during sensitization - mainly on processes occurring in the body itself, both physiological and mental. Thus, sensitization is an increase in the sensitivity of the senses under the influence of internal factors.

There are two main directions for increasing sensitivity according to the type of sensitization. One of them is of a long-term, permanent nature and depends primarily on sustainable changes occurring in the body, the second is of an unstable nature and depends on temporary effects on the body.

The first group of factors that change sensitivity include: age, endocrine changes, dependence on the type of nervous system, and the general condition of the body associated with compensation of sensory defects.

Studies have shown that the sensitivity of the sensory organs increases with age, reaching its maximum by 20-30 years, in order to gradually decrease thereafter.

Essential features of the functioning of the senses depend on the type of human nervous system. It is known that people with a strong nervous system exhibit greater endurance and less sensitivity, while people with a weak nervous system and less endurance have greater sensitivity.

The endocrine balance in the body is very important for sensitivity. For example, during pregnancy, olfactory sensitivity sharply worsens, while visual and auditory sensitivity decreases.

Compensation for sensory defects leads to increased sensitivity. So, for example, the loss of vision or hearing is to a certain extent compensated by the exacerbation of other types of sensitivity. People deprived of vision have a highly developed sense of touch and are able to read with their hands. This process of reading with your hands has a special name - haptics. In people who are deaf, vibration sensitivity develops greatly. For example, the great composer Ludwig Van Beethoven, in the last years of his life, when he lost his hearing, used vibration sensitivity to listen to musical works.

The second group of factors that change sensitivity includes pharmacological influences, conditioned reflex increases in sensitivity, the influence of a second signaling system and setting, the general state of the body associated with fatigue, as well as the interaction of sensations.

There are substances that cause a distinct exacerbation of sensitivity. These include, for example, adrenaline, the use of which causes stimulation of the autonomic nervous system. A similar effect, exacerbating the sensitivity of receptors, can have phenamine and a number of other pharmacological agents.

Conditioned reflex increases in sensitivity include situations in which there were harbingers of a threat to the functioning of the human body, fixed in memory by previous situations. For example, a sharp increase in sensitivity is observed among members of operational groups who participated in combat operations during subsequent combat operations. Taste sensitivity is heightened when a person finds himself in an environment similar to the one in which he previously participated in a rich and pleasant feast.

An increase in the sensitivity of the analyzer can also be caused by exposure to secondary signal stimuli. For example: a change in the electrical conductivity of the eyes and tongue in response to the words “sour lemon,” which in fact occurs when directly exposed to lemon juice.

An aggravation of sensitivity is also observed under the influence of the setting. Thus, hearing sensitivity increases sharply when anticipating an important phone call.

Changes in sensitivity also occur in a state of fatigue. Fatigue first causes an exacerbation of sensitivity, that is, a person begins to acutely sense extraneous sounds, smells, etc. that are not related to the main activity, and then with the further development of fatigue, a decrease in sensitivity occurs.

A change in sensitivity can also be caused by the interaction of different analyzers.

The general pattern of interaction between analyzers is that weak sensations cause an increase, and strong ones cause a decrease in the sensitivity of the analyzers during their interaction. Physiological mechanisms in this case underlying sensitization. - these are the processes of irradiation and concentration of excitation in the cerebral cortex, where the central sections of the analyzers are represented. According to Pavlov, a weak stimulus causes an excitation process in the cerebral cortex, which easily radiates (spreads). As a result of irradiation, the sensitivity of other analyzers increases. When exposed to a strong stimulus, a process of excitation occurs, which, on the contrary, causes a process of concentration, which leads to inhibition of the sensitivity of other analyzers and a decrease in their sensitivity.

When analyzers interact, intermodal connections may arise. An example of this phenomenon is the occurrence of panic fear when exposed to ultra-low frequency sound. The same phenomenon is confirmed when a person feels the effects of radiation or feels someone staring at their back.

A voluntary increase in sensitivity can be achieved in the process of targeted training activities. For example, an experienced turner is able to “by eye” determine the millimeter dimensions of small parts; tasters of various wines, perfumes, etc., even with extraordinary innate abilities, in order to become real masters of their craft, are forced to train the sensitivity of their analyzers for years.

The considered types of sensitivity variability do not exist in isolation precisely because analyzers are in constant interaction with each other. Associated with this is the paradoxical phenomenon of synesthesia.

Synesthesia is the occurrence, under the influence of stimulation of one analyzer, of a sensation characteristic of another (for example: cold light, warm colors). This phenomenon is widely used in art. It is known that some composers possessed the ability of “color hearing,” including Alexander Nikolaevich Scriabin, who wrote the first color-musical work in history - the Prometheus symphony, presented in 1910 and including the light part. Lithuanian painter and composer Čiurlionis Mikolojus Konstantinas (1875-1911) is known for his symbolic paintings, in which he reflected visual images of his musical works - “Sonata of the Sun”, “Sonata of Spring”, “Symphony of the Sea”, etc.

The phenomenon of synesthesia characterizes the constant interconnection of the body’s sensory systems and the integrity of the sensory reflection of the world.

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STRUCTURE, FUNCTIONS AND PROPERTIES OF ANALYZERS (SENSORY SYSTEMS)

The question of the process of transforming sensory stimuli into sensations, their localization, as well as the mechanism and place of formation of a general idea of an object (perception) in modern psychophysiology is resolved on the basis of the teachings of I.P. Pavlova about analyzers (sensory systems).

The analyzer (sensory system) is a single physiological system that is adapted to perceive stimuli from the external or internal world, process them into a nerve impulse and form sensations and perceptions.

The following analyzers (sensory systems) are distinguished: pain, vestibular, motor, visual, introceptive, skin, olfactory, auditory, temperature and others.

Any analyzer has a fundamentally identical structure (Fig. 14.1). It consists of three parts:

1. The initial - perceiving part of the analyzer is represented by receptors. They developed in the process of evolution as a result of the increased sensitivity of some cells to a certain type of energy (thermal, chemical, mechanical, etc.). The stimulus to which the receptor is specially adapted is called adequate; all others will be inadequate.

Rice. 14.1.

Depending on the location, the following receptors are distinguished:

A) Exteroceptors (visual, auditory, olfactory, gustatory, tactile), which lie on the surface of the body and respond to external influences, providing an influx of sensory information from the external environment. B) Interoreceptors are located in the tissues of internal organs in the lumen of large vessels (for example, chemoreceptors, baroreceptors) and are sensitive to certain parameters of the internal environment (concentration of chemically active substances, blood pressure, etc.); they are important for obtaining information about the functional state of the body and its internal environment. C) Proprioceptors lie in muscles, tendons and perceive information about the degree of stretching and contraction of muscles, due to which a “body sense” is formed (a sense of one’s own body and the relative location of its parts).

The perceptive part of the analyzer is sometimes represented by the corresponding sensory organ (eye, ear, etc.). A sensory organ is a structure containing receptors and auxiliary structures that provide the perception of specific energy. For example, the eye contains visual receptors and structures such as the eyeball, membranes of the eyeball, eye muscles, pupil, lens, vitreous body, which provide the effect of light on the visual receptors.

The function of the receptors is to perceive the energy of the stimulus and convert it into nerve impulses of a certain frequency (sensory code).

2. The conductive section of each analyzer is represented by a sensory nerve, along which excitation goes from the receptors to the subcortical and cortical centers of this analyzer. In this case, two interconnected pathways are distinguished: the first, the so-called specific analyzer pathway, goes through specific nuclei of the brain stem and plays a major role in the transmission of sensory information and the occurrence of sensations of a certain type; the second, nonspecific pathway is represented by neurons of the reticulatory formation. The flow of impulses traveling along it changes the functional state of the structures of the spinal cord and brain, i.e. has an activating effect on nerve centers. The role of the conductive section of each analyzer is not limited to transmitting excitation from receptors to the cortex: it also takes part in the occurrence of sensations. For example, the subcortical centers of the visual analyzer, located in the midbrain (in the superior colliculus), receive information from visual receptors and tune the organ of vision to more accurately perceive visual information. In addition, already at the level of the diencephalon, unclear, rough sensations arise (for example, light and shadow, light and dark objects). Considering the conductive part of the analyzers as a whole, you should pay attention to the thalamus. In this part of the diencephalon, the afferent (sensitive) pathways of all analyzers (with the exception of the olfactory one) converge. This means that the thalamus receives information from extero-, proprio- and interoreceptors about the environment and the state of the body.

Thus, all sensory information is collected and analyzed in the thalamus. Here it is partially processed and in this processed form is transferred to various areas of the cortex. Most sensory information does not reach the higher part of the central nervous system (and therefore does not cause clear and conscious sensations), but becomes a component of motor and emotional responses and, possibly, “material” for intuition.

3. The central section of each analyzer is located in a certain area of the cerebral cortex. For example:
- visual analyzer - in the occipital lobe of the cortex;
- auditory and vestibular analyzers - in the temporal lobe;
- olfactory analyzer - in the hippocampus and temporal lobe;
- taste analyzer - in the parietal lobe;
- tactile analyzer (somatosensory system) - in the posterior central gyrus of the parietal lobe (somatosensory zone);
- motor analyzer - in the anterior central gyrus of the frontal lobe (motor area) (Fig. 14.2).

Rice. 14.2.

Each analyzer contains descending, efferent neurons that “turn on” motor reactions. For example, visual information arriving at the superior colliculus causes “local” reflexes—involuntary eye movements behind a moving object, one of the elements of the orienting reflex. In the cortex, the central ends of all analyzers are connected to the motor zone, which is the central section of the motor analyzer. Thus, the motor zone receives information from all sensory systems of the body and serves as a link in interanalyzer relationships, thereby ensuring a connection between sensations and movements.

The structural elements of analyzers are not isolated in the nervous system, but are anatomically and functionally connected with speech centers, with the limbic system, subcortical sections, with autonomic centers of the trunk, etc., which ensures the relationship of sensations with emotions, movements, behavior, speech, and explains influence of sensory information on the human body.

Operating principles of analyzers (sensory systems)

Analyzers are figuratively called windows to the world, or channels of communication between a person and the outside world and his own body. Already “at the input” the information is analyzed, which is achieved by the selective response of receptors.

Within one modality there is a huge variety of signals: for example, sounds vary in pitch, timbre, origin; visual information - by color, brightness, shape, size, etc. The ability to perceive the difference between them is due to the fact that different sensory signals arise in the analyzers for different stimuli. This function is called signal discrimination. It is achieved by the formation of nerve impulses of different frequencies at the receptor level (sensory code) and the inclusion of differentiation processes at all levels of the sensory system - from receptors to the cortex. Essentially, signal discrimination is an integral part of the analysis process.

As the child develops and his interaction with the outside world becomes more complex, differentiations become more subtle due to the development of differentiation inhibition in the cortex. This is also facilitated by the development of each analyzer separately, as well as the complication of their interaction. Movement plays a major role in this process: motor differentiation helps sensory differentiation. Thus, to distinguish visual information, eye movements are necessary, which inevitably accompany the process of viewing an object, as well as various hand positions that arise when feeling it. The same principle applies to the formation of phonemic hearing. To distinguish speech sounds well - phonemes - it is not enough to hear the speech of another person (even with excellent diction of the speaker), you also need to have a good feel for your own articulatory apparatus (lips, tongue, palate, larynx, cheeks), and feel the differences in its positions when reproducing sounds. Many methods of teaching children of preschool and primary school age, as well as correctional techniques, rely on this mechanism.

A subtle analysis of stimuli requires the activity of the subject of cognition himself. If a person himself wants to participate in a particular activity, and it evokes positive emotions (interest, joy), then his sensory sensitivity to various signals increases significantly. Voluntary attention plays an active role in this process. This result is achieved due to control from the cerebral cortex and the nearest subcortex of the underlying sections of the analyzers with the help of efferent neurons (see Fig. 14.1).

Thus, sensory processes cannot be considered only as a physiological reflection of the objective properties of objects, since they also reflect a subjective factor - the needs, emotions and associated behavior of the subject, which influence the emerging sensory images.

One of the questions that arises when studying sensory systems is how information is transmitted in analyzers. In the receptors, under the influence of a stimulus, nerve impulses of a certain frequency are formed, which propagate along the afferent pathways in groups - “volleys” or “packs” (sensory frequency code). It is believed that the number of impulses and their frequency is the language with which receptors transmit information to the brain about the properties of the reflected object.

At the present stage, it is impossible to establish a clear correspondence between one or another property of the stimulus and the method of its fixation in the nervous system. Existing scientific information describes only some general principles of information transmission in the nervous system (Fig. 14.3).

Rice. 14.3.

The scheme of this process is as follows. The sensory code in the form of nerve impulses comes from receptors to the subcortical centers of the brain, where they are partially decoded, filtered, and then sent to specific centers of the cortex - the centers of the analyzer, where sensations are born. Then a synthesis of various sensations occurs, from where impulses are sent to the hippocampus (memory) and the structures of the limbic system (emotions), and then return to the cortex, including the motor center of the frontal lobe. The excitement is summed up and a sensory image is built.

Thus, not only sensations, but also movements, memory and emotions are involved in constructing a holistic image of an object and recognizing it. Previously encountered impressions (sensory images) are stored in memory, and emotions signal the significance of the information received.

Perception does not arise mechanically or purely physiologically. The subject himself, his consciousness, his attention take an active part in its formation. In other words, the person himself must pay attention to the object, isolate it, voluntarily switch attention from the whole to the parts and have a desire for this, some kind of goal. That is why children's education can only be successful when it makes them want to know what is offered to them, if it is of interest to them.

Properties of the conductor section of analyzers

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

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

2. From each specific sensory pathway, collaterals extend 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 nonspecific pathways, in addition, the reticular formation is the site of inter-analyzer interaction.

3. There is a multichannel conduction of excitation from receptors to the cortex (specific and nonspecific paths), which ensures the reliability of information transfer.

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

spinal or stem (medulla oblongata);
thalamus;
the corresponding projection zone of the cerebral cortex.

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

5. In addition to specific and nonspecific 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 a stimulus, etc. Thus, the sensory function is carried out on the basis of the interconnected activity of specific, nonspecific and associative brain formations, which ensure the formation of adequate adaptive behavior of the body.

Central, or cortical, division 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 zones of the cortex are distinguished. Excitation from the corresponding receptors to the primary zones is directed along fast-conducting specific pathways, while activation of the secondary and tertiary (associative) zones occurs along polysynaptic nonspecific pathways. In addition, the cortical zones are interconnected by numerous associative fibers.

CLASSIFICATION OF RECEPTORS

The classification of receptors is based primarily on on the nature of sensations that arise in humans when they are irritated. Distinguish visual, auditory, olfactory, gustatory, tactile receptors, thermoreceptors, proprioceptors and vestibuloreceptors (receptors for 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 exteroceptors, And internal , or interoreceptors. Exteroceptors include auditory, visual, olfactory, taste and tactile receptors. Interoreceptors include vestibuloreceptors and proprioceptors (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 stimulation (visual, auditory and olfactory), and contact – excited by direct contact with a 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 are 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 tension, osmolarity and pH, glucose levels and other substances). Such receptors are found in the mucous membrane of the tongue and nose, carotid and aortic bodies, hypothalamus and medulla oblongata.

· 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, midbrain, medulla oblongata and spinal cord.

· Photoreceptors The retina of the eye perceives light (electromagnetic) energy.

· Nociceptors , the excitation of which is accompanied by painful sensations (pain receptors). The irritants of these receptors are mechanical, thermal and chemical (histamine, bradykinin, K + , H +, etc.) factors. Painful stimuli are perceived by free nerve endings, which are found in the skin, muscles, internal organs, dentin, and blood vessels. From a psychophysiological point of view, receptors are divided according to the sense organs and the sensations generated into visual, auditory, gustatory, olfactory And tactile.

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

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

Secondary sensory receptors respond to the action of a stimulus only by the appearance of a receptor potential, the magnitude of which determines the amount of mediator released by these cells. With its help, secondary receptors act on the nerve endings of sensitive neurons, generating action potentials depending on the amount of mediator released from the secondary 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 often classified as primary receptors, but their lack of ability to generate action potentials indicates their similarity to secondary receptors.

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

Most receptors are excited in response to stimuli of only one physical nature and therefore belong to monomodal . They can also be excited by some inappropriate 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 in such cases it is impossible to obtain qualitatively distinct sensations.

Along with monomodal there are multimodal receptors, the adequate stimuli of which can be irritants of different nature. This type of receptor includes some pain receptors, or nociceptors (Latin nocens - harmful), which can be excited by mechanical, thermal and chemical stimuli. Thermoreceptors have polymodality, reacting to an increase in potassium concentration 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, thanks to the interaction of the visual analyzer with other analyzers, quite 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 external world, the degree of illumination and the length of daylight hours.

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

1. Peripheral section - the eyeball, in particular - the retina (receives light stimulation)

2. Conducting section - axons of ganglion cells - optic nerve - optic chiasm - optic tract - diencephalon (geniculate bodies) - midbrain (quadrigeminal) - thalamus

3. Central section - occipital lobe: area of the calcarine sulcus and adjacent gyri.

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

After the chiasm, 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 cerebral peduncles and end in the external 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 pathway and the primary visual center.

The ganglion cells of the external geniculate body end with the fibers of the optic tract and begin with the fibers of the central neuron, which pass through the posterior knee of the internal capsule and then, as part of the Graziole bundle, are directed to the occipital lobe cortex, the cortical visual centers, in the area of the calcarine sulcus.

So, the neural pathway of the visual analyzer begins in the layer of ganglion cells of the retina 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. The central neuron begins here and ends in the occipital lobe of the brain.

The physiological significance of the visual pathway is determined by its function in conducting 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.

To see an object clearly, it is necessary that the rays of each point of it be focused on the retina. If you look into the distance, then close objects are seen unclearly, blurry, since the rays from nearby points are focused behind the retina. It is impossible to see objects at different distances from the eye with equal clarity 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 rays passing through the peripheral parts of the lens are refracted more strongly than 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 the 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), i.e. the ability of the eye to refract, is measured in conventional units - diopters. Diopter is the refractive power of a lens in which parallel rays, after refraction, converge at a focus at a distance of 1 m.

We see the world around us clearly when all parts of the visual analyzer “work” harmoniously and without interference. In order for the image to be sharp, the retina obviously must be in the back focus of the eye's optical system. Various disturbances in 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, farsightedness, age-related farsightedness and astigmatism (Fig. 5).

Fig.5. Ray path for 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 consider two separate points visible at an angle of 1 minute.

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

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

Astigmatism due to the fact that, due to its innate characteristics, the optical system of the eye (cornea and lens) refracts rays unequally 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). Thus, if the curvature of the corneal surface in the vertical section is greater than in the horizontal section, 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 section. Therefore, light rays passing through an astigmatic eye will be focused in different planes: if the horizontal lines of an object are focused on the retina, then the vertical lines will be in front of it. Wearing cylindrical lenses, selected taking into account the actual defect of the optical system, to a certain extent compensates for this refractive error.

Myopia and farsightedness caused by changes in the length of the eyeball. With normal refraction, the distance between the cornea and the fovea (macula) is 24.4 mm. With myopia (myopia), the longitudinal axis of the eye is greater than 24.4 mm, so 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 glasses in front of myopic eyes, which will push the focused image onto the retina. In the farsighted eye, the longitudinal axis of the eye is shortened, i.e. 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 accommodative effort, i.e. an increase in the convexity of the lens. Therefore, a farsighted person strains the accommodative muscle, examining not only close, but also distant objects. When viewing close objects, the accommodative efforts of farsighted people are insufficient. Therefore, to read, farsighted people must wear glasses with biconvex lenses that enhance the refraction of light.

Refractive errors, in particular myopia and farsightedness, are also common among animals, for example, 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. Located in subcutaneous fat. They are quickly adapting (they react only at the moment the impact begins), that is, they register the force of pressure. They have large receptive fields, that is, they represent gross sensitivity.
Meissner's corpuscles are pressure receptors located in the dermis. They are a layered structure with a nerve ending running between the layers. They are quickly adaptable. They have small receptive fields, that is, they represent subtle sensitivity.
Merkel discs are unencapsulated pressure receptors. They are slowly adapting (react throughout the entire duration of exposure), that is, they record the duration of pressure. They have small receptive fields.
Hair follicle receptors - respond to hair deviation.
Ruffini endings are stretch receptors. They are slow to adapt and 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, ruptures, stretching, radiation exposure, chemical irritants; Immune function of the skin. T lymphocytes present in the skin recognize exogenous and endogenous antigens; Largehans 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 stimulation; 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 medications; The secretory function is carried out by the sebaceous and sweat glands of the skin, secreting sebum and sweat, which, when mixed, form a thin film of water-fat emulsion on the surface of the skin; Respiratory function is the ability of the skin to absorb oxygen and release carbon dioxide, which increases with increasing 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 covering 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.

Classification of pain. There are two types of pain:

1. Somatic, which occurs when the skin and musculoskeletal system are damaged. 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 manifests itself in tingling and pinching. Deep pain, as a rule, is dull, poorly localized, tends to radiate into surrounding structures, and is accompanied by unpleasant sensations, nausea, severe sweating, and a drop in blood pressure.

2.Visceral, which occurs when internal organs are damaged and has a similar picture with deep pain.

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

As an example projection pain A sharp blow to the ulnar nerve can be given. Such a blow causes an unpleasant, difficult to describe sensation that spreads to those parts of the arm 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 area of the receptors of this sensory pathway. One of the 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 cartilaginous discs. Afferent impulses in nociceptive fibers in this pathology cause pain sensations that are projected to the area associated with the injured spinal nerve. Projection (phantom) pain also includes pain that patients feel in the area of the removed part of the limb.

Referred pain Pain sensations are called not in the internal organs from which pain signals come, but in certain parts of the skin surface (Zakharyin-Ged zone). So, with angina pectoris, in addition to pain in the heart area, pain is felt in the left arm and shoulder blade. Referred pain differs from projection pain in that it is caused not 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 conducting pain impulses from the receptors of the affected organ and the receptors of the corresponding area of the skin converge on the same neuron of the spinothalamic tract. 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.

Antipain (antinociceptive) system. In the second half of the twentieth century, evidence was obtained of 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 have a descending activating effect on inhibitory neurons of the spinal cord. These include the central gray matter, raphe nuclei, locus coeruleus, lateral reticular nucleus, paraventricular and preoptic nuclei of the hypothalamus. The somatosensory area of the cortex unites and controls the activity of the structures of the analgesic system. Impairment of this function can cause unbearable pain.

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

Endogenous stimulants of opiate receptors are enkephalins and endorphins. Some hormones, for example corticoliberin, can stimulate their formation. Endorphins act primarily through morphine receptors, which are especially numerous in the brain: in the central gray matter, raphe nuclei, and middle thalamus. Enkephalins act through receptors located primarily 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 occurs when super-strong stimuli act on the receptors of the five senses. 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, the modern theory of pain uses the position about the role of central summation and convergence in the mechanisms of pain. The most important achievement in the development of modern pain theory is the study of the mechanisms of central pain perception and the body's anti-pain system.

Functions of proprioceptors

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

Muscle spindles human, are oblong 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 several units to hundreds.

Thus, muscle spindles, as sensors of the state of muscle strength and the speed 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 spindles under 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. During active muscle contraction, a decrease in its length has a deactivating effect on the spindle receptors, and the excitation of gamma motor neurons, accompanying the excitation of alpha motor neurons, leads to reactivation of the receptors. As a result, impulses from spindle receptors during movement depend on the length of the muscle, the speed of its shortening and the force of contraction.

Golgi tendon organs (receptors) in humans are located in the area of connection between the muscle fibers and the tendon, sequentially relative to the muscle fibers.

The tendon organs are an elongated fusiform or cylindrical structure, the length of which in humans can reach 1 mm. This is the primary sensory receptor. Under resting conditions, i.e. when the muscle is not contracted, background impulses come from the tendon organ. Under conditions of muscle contraction, the frequency of impulses increases in direct proportion to the magnitude of the 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 tendon organs to muscle fibers (and in some cases to muscle spindles), stretching of tendon mechanoreceptors occurs when 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.

Joint receptors react to the position of the joint and to changes in the joint angle, thus participating in the feedback system from the motor system and in its control. 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 joint receptors send information about the size of the joint angle, i.e., about the position of the joint. Their impulse continues throughout the entire period of maintaining a given angle. The greater the angle shift, the higher the frequency. Other joint receptors are excited only at the moment of movement in the joint, i.e. they send information about the speed of movement. The frequency of their impulses increases with the increase in the rate of change in the joint angle.

Conductive and cortical sections proprioceptive analyzer of mammals and humans. Information from muscle, tendon and joint receptors enters through the axons of the first afferent neurons located in the spinal ganglia into the spinal cord, where it is partially switched to alpha motor neurons or interneurons (for example, to Renshaw cells), and partially sent 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 through 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.

The axons of thalamic neurons (third-order neurons) end in the cerebral cortex, mainly in the somatosensory cortex (postcentral gyrus) and in the area of the Sylvian fissure (areas S-1 and S-2, respectively), and also partially in the motor ( prefrontal) region of the cortex. This information is used quite widely by the motor systems of the brain, including for making decisions about the intention of movement, as well as for its implementation. In addition, based on 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 receptors of muscle spindles, tendon organs, joint capsules and tactile receptors of the skin are called kinesthetic, i.e., informing about body movement. Their participation in the voluntary regulation of movements varies. Signals from joint receptors cause a noticeable reaction in the cerebral cortex and are well recognized. Thanks to them, a person perceives differences in joint movements better than differences in the degree of muscle tension during static positions or supporting weight. Signals from other proprioceptors, arriving primarily in the cerebellum, provide unconscious regulation, subconscious control of movements and postures.

Thus, proprioceptive sensations give a person the opportunity to perceive changes in the position of individual parts of the body at rest and during movements. Information coming from the 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, communication with the continuously 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, ensure the formation of sensations and ideas, as well as specific forms of adaptive behavior.

The idea of sensory systems was formulated by I. P. Pavlov in the doctrine of analyzers in 1909 during his study of higher nervous activity. Analyzer- a set of central and peripheral formations that perceive and analyze changes in the external and internal environments of the body. The concept of “sensory system”, which appeared later, replaced the concept of “analyzer”, including the mechanisms of regulation of its various departments using direct and feedback connections. Along with this, the concept of “sense organ” still exists as a peripheral formation that perceives and partially analyzes environmental factors. The main part of the sensory organ is the receptors, equipped with auxiliary structures that ensure optimal perception.

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

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

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

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

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

Internal (visc

Sensory system organs and functions. Human sensory systems (analyzers)

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