Types of tactile receptors. Tactile receptors

Skin receptors are responsible for our ability to feel touch, heat, cold and pain. Receptors are modified nerve endings that can be either free non-specialized or encapsulated complex structures that are responsible for a certain type of sensitivity. Receptors perform a signaling role, so they are necessary for a person to effectively and safely interact with the external environment.

The main types of skin receptors and their functions

All types of receptors can be divided into three groups. The first group of receptors is responsible for tactile sensitivity. These include the bodies of Pacini, Meissner, Merkel and Ruffini. The second group is
thermoreceptors: Krause flasks and free nerve endings. The third group includes pain receptors.

The palms and fingers are more sensitive to vibration: due to the large number of Pacini receptors in these areas.

All types of receptors have different zones in terms of the width of sensitivity, depending on the function they perform.

Skin receptors:
. skin receptors responsible for tactile sensitivity;
. skin receptors that respond to changes in temperature;
. nociceptors: skin receptors responsible for pain sensitivity.

Skin receptors responsible for touch sensitivity

There are several types of receptors responsible for tactile sensations:
. Pacinian corpuscles are receptors that quickly adapt to changes in pressure and have wide receptive fields. These receptors are located in the subcutaneous fat and are responsible for gross sensitivity;
. Meissner's bodies are located in the dermis and have narrow reception fields, which determines their perception of fine sensitivity;
. Merkel bodies - slowly adapt and have narrow receptor fields, and therefore their main function is to sense the structure of the surface;
. Ruffini's bodies are responsible for the sensation of constant pressure and are located mainly in the area of ​​\u200b\u200bthe soles of the feet.

Also, receptors located inside the hair follicle are separately isolated, which signal the deviation of the hair from its original position.

Skin receptors that respond to changes in temperature

According to some theories, there are different types of receptors for the perception of heat and cold. Krause flasks are responsible for the perception of cold, and free nerve endings are responsible for the perception of hot. Other theories of thermoreception claim that it is the free nerve endings that are designed to sense temperature. In this case, thermal stimuli are analyzed by deep nerve fibers, while cold stimuli are analyzed by superficial ones. Between themselves, the temperature sensitivity receptors form a "mosaic" consisting of cold and heat spots.

Nociceptors: skin receptors responsible for pain sensitivity

At this stage, there is no final opinion regarding the presence or absence of pain receptors. Some theories are based on the fact that free nerve endings, which are located in the skin, are responsible for the perception of pain.

Prolonged and strong pain stimulation stimulates the emergence of a stream of outgoing impulses, and therefore, adaptation to pain slows down.

Other theories deny the presence of separate nociceptors. It is assumed that tactile and temperature receptors have a certain threshold of irritation, above which pain occurs.

Tactile receptors, or touch and pressure receptors are located on the surface of the skin.

Touch receptors are Meissner's bodies, located in the skin papillae, and Merkel discs, located especially in large numbers on the fingertips and lips. On skin covered with hair, the hair is highly sensitive to touch. This is due to the fact that the hair root is wrapped around the nerve plexus and any touch to the hair is transmitted to this plexus, causing its excitation. Shaving hair greatly reduces the sensitivity of the skin to touch. Pressure receptors are Pachinian corpuscles.

The conductors of tactile reception are thick myelin fibers. Electrophysiological registration of action potentials showed that even with a very short stimulation tactile receptors not one impulse occurs in them, but a whole series of discharges.

Adaptation of touch receptors. Tactile receptors way to quickly adapt, so only the change in pressure is felt, not the pressure itself. If a load is placed on the plantar pad of a cat's paw, then nerve impulses arise in the receptor, the frequency of which can reach 250-350 pulses / sec. This impulsation lasts a few seconds and stops due to the onset of adaptation. In humans, a decrease in the frequency of impulses is accompanied by a decrease in the strength of sensation.
The rate of adaptation of different skin receptors is not the same. The receptors located at the roots of the hair and Pacinian bodies adapt most quickly.
Due to adaptation, a person feels the pressure of clothing only at the moment when he puts it on or when the clothes rub against the skin during movement.

Localization of tactile sensations. A person very accurately relates all sensations of touch and pressure to a specific place on the skin. Localization of tactile sensations is developed through experience under the control of other senses, mainly vision and muscular sense. For proof, we can cite the famous experiment of Aristotle: touching a small ball with crossed index and middle fingers gives the sensation of touching two balls, since everyday experience teaches that only two separate balls can touch the inside of the index finger and the outside of the middle finger at the same time.

Measurement of tactile sensitivity. Tactile sensitivity is developed very differently in different parts of the skin. Tactile sensitivity is measured with a Frey esthesiometer, which determines the pressure required to stimulate the receptors and produce sensations.

The threshold of irritation of the most sensitive areas of the skin is 50 mg, the least sensitive - 10 g. The sensitivity of the lips, nose, tongue is the highest, the sensitivity of the back, soles of the feet, and the abdomen is the lowest.

Thresholds of space. When touching two points of the skin at the same time, two touches are not always felt: if these two points lie close to each other, then only one touch may be felt. That smallest distance between two points of the skin, upon stimulation of which there is a sensation of two touches, is called the threshold of space.

The thresholds of space are measured using a compass, or Weber's esthesiometer, which is a compass with a scale indicating the distance between its legs in millimeters.

Structural and functional characteristics of the skin analyzer

Connection of cutaneous and visceral pathways in:
1 - Gaulle's bundle;
2 - Burdakh's bundle;
3 - back spine;
4 - front spine;
5 - spinothalamic tract (conduction of pain sensitivity);
6 - motor axons;
7 - sympathetic axons;
8 - front horn;
9 - propriospinal path;
10 - rear horn;
11 - visceroreceptors;
12 - proprioceptors;
13 - thermoreceptors;
14 - nociceptors;
15 - mechanoreceptors

Its peripheral section is located in the skin. These are pain, touch and temperature receptors. There are about a million pain receptors. When excited, they create a feeling that causes the body's defenses.

Touch receptors cause the sensation of pressure and touch. These receptors play an essential role in the knowledge of the surrounding world. With the help, we determine not only whether the surface of objects is smooth or rough, but also their size, and sometimes even their shape.

No less important is the sense of touch for motor activity. In motion, a person comes into contact with support, objects, air. The skin stretches in some places, shrinks in others. All this irritates the tactile receptors. The signals from them, coming to the sensory-motor zone, the cerebral cortex, help to feel the movement of the whole body and its parts. Temperature receptors are represented by cold and heat points. They, like other skin receptors, are unevenly distributed.

The skin of the face and abdomen is most sensitive to the effects of temperature irritants. The skin of the legs compared to the skin of the face is two times less sensitive to cold and four times less sensitive to heat. Temperature helps to feel the structure of the combination of movements and speed. This happens because with a rapid change in the position of body parts or a high speed of movement, a cool breeze arises. It is perceived by temperature receptors as a change in skin temperature, and by tactile receptors as a touch of air.

The afferent link of the skin analyzer is represented by the nerve fibers of the spinal nerves and the trigeminal nerve; the central sections are mainly in, and the cortical representation is projected into the postcentral.

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

Tactile Analyzer is part of the skin analyzer. It provides sensations of touch, pressure, vibration and tickling. The peripheral section is represented by various receptor formations, the irritation of which leads to the formation of specific sensations. On the surface of the skin devoid of hair, as well as on the mucous membranes, special receptor cells (Meissner bodies) located in the papillary layer of the skin react to touch. On the skin covered with hair, the hair follicle receptors, which have moderate adaptation, respond to touch. Receptor formations (Merkel discs) located in small groups in the deep layers of the skin and mucous membranes react to pressure. These are slowly adapting receptors. Adequate for them is the deflection of the epidermis under the action of a mechanical stimulus on the skin. Vibration is perceived by Pacini's bodies, located both in the mucous and on parts of the skin not covered with hair, in the adipose tissue of the subcutaneous layers, as well as in the articular bags, tendons. Pacini corpuscles have a very fast adaptation and respond to acceleration when the skin is displaced as a result of mechanical stimuli, several Pacini corpuscles are simultaneously involved in the reaction. Tickling is perceived by free-lying, non-encapsulated nerve endings located in the superficial layers of the skin.

Skin receptors: 1 - Meissner's body; 2 - Merkel disks; 3 - Paccini's body; 4 - hair follicle receptor; 5 - tactile disk (Pincus-Iggo body); 6 - the end of Ruffini

Each type of sensitivity corresponds to special receptor formations, which are divided into four groups: tactile, thermal, cold and pain. The number of different types of receptors per unit surface is not the same. On average, there are 50 painful, 25 tactile, 12 cold and 2 heat points per 1 square centimeter of the skin surface. Skin receptors are localized at different depths, for example, cold receptors are located closer to the skin surface (at a depth of 0.17 mm) than thermal receptors, located at a depth of 0.3–0.6 mm.

Absolute specificity, i.e. the ability to respond only to one type of irritation is characteristic only of some receptor formations of the skin. Many of them react to stimuli of different modality. The occurrence of various sensations depends not only on which receptor formation of the skin was irritated, but also on the nature of the impulse coming from this receptor in.

The sense of touch (touch) arises with light pressure on the skin, when the skin surface comes into contact with surrounding objects, it makes it possible to judge their properties and navigate in the external environment. It is perceived by tactile bodies, the number of which varies in different parts of the skin. An additional receptor for touch is the nerve fibers that braid the hair follicle (the so-called hair sensitivity). The feeling of deep pressure is perceived by lamellar bodies.

Pain is perceived mainly by free nerve endings located both in the epidermis and in the dermis.

The thermoreceptor is a sensitive nerve ending that responds to changes in ambient temperature, and when located deep, to changes in body temperature. Temperature sensation, the perception of heat and cold, is of great importance for the reflex processes that regulate body temperature. It is assumed that thermal stimuli are perceived by Ruffini bodies, and cold stimuli are perceived by Krause end flasks. There are much more cold points on the entire surface of the skin than thermal ones.

Skin receptors

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

Schematic incision of the skin: 1 - corneal layer; 2 - clean layer; 3 - granulosa layer; 4 - basal layer; 5 - muscle that straightens the papilla; 6 - dermis; 7 - hypodermis; 8 - artery; 9 - sweat gland; 10 - adipose tissue; 11 - hair follicle; 12 - vein; 13 - sebaceous gland; 14 - Krause body; 15 - dermal papilla; 16 - hair; 17 - sweat time

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

Tactile sensitivity (touch), the animal's perception of touch, pressure, stretching. On the surface of the body of animals there is a huge number of receptors, which are the endings of sensitive nerve fibers. According to the nature of sensitivity, receptors are divided into pain, temperature (heat and cold) and tactile (mechanoreceptors).

Touch is the ability of animals to perceive various external influences, carried out by the receptors of the skin and the musculoskeletal system.

The tactile sensation can be varied, as it arises as a result of a complex perception of the various properties of the stimulus acting on the skin and subcutaneous tissues. Through touch, the shape, size, temperature, consistency of the stimulus, the position and movement of the body in space, etc. are determined. The basis of touch is the stimulation of specialized receptors and the transformation of incoming signals in the central nervous system into the appropriate type of sensitivity (tactile, temperature, pain).

1. Skin analyzer. The receptors of this analyzer are:

free nerve endings in the epithelium, which perceive pain and temperature sensations, pressure and serve as chemoreceptors;

tactile cells entwined with a network of nerve fibers;

tactile bodies formed by groups of tactile cells enclosed in a connective tissue membrane. They are best developed on the fingers of climbing mammals, at the end of an elephant's trunk, the stigma of a mole, etc.

But the main receptors that perceive these stimuli and partly the position of the body in space in mammals are hair, especially whiskers. Vibrissae react not only to touches to surrounding objects, but also to air vibrations. In norniks, which have a wide surface of contact with the walls of the burrow, vibrissae, except for the head, are scattered throughout the body. In climbing forms, for example, in squirrels and lemurs, they are also located on the ventral surface and on parts of the limbs that come into contact with the substrate when moving through trees.

Tactile sensation is due to irritation of mechanoreceptors (Pacini and Meissner bodies, Merkel discs, etc.) located in the skin at some distance from each other. Animals are able to quite accurately determine the location of irritations: crawling of insects on the skin or their bites cause a sharp motor and defensive reaction. The highest concentration of receptors in most animals is noted in the head region, respectively, areas of the scalp, mucous membranes of the oral cavity of the lips, eyelids and tongue have the highest sensitivity to touch. In the first days of life of a young mammal, the main tactile organ is the oral cavity. Touching the lips causes him to suck.

Continuous action on mechano- and thermoreceptors leads to a decrease in their sensitivity, i.e. they quickly adapt to these factors. Skin sensitivity is closely related to internal organs (stomach, intestines, kidneys, etc.). So it is enough to apply irritation to the skin in the stomach area in order to get an increased acidity of gastric juice.

When the pain receptors are stimulated, the resulting excitation is transmitted along the sensory nerves to the cerebral cortex. In this case, the incoming impulses are identified as emerging pain. The feeling of pain is of great importance: pain signals disorders in the body. The excitation threshold of pain receptors is species-specific. So, in dogs it is somewhat lower than, for example, in humans. Irritation of pain receptors causes reflex changes: increased release of adrenaline, increased blood pressure and other phenomena. Under the action of certain substances, such as novocaine, pain receptors are turned off. This is used for local anesthesia during operations.

Irritation of the temperature receptors of the skin is the cause of the sensation of heat and cold. Two types of thermoreceptors can be distinguished: cold and heat. Temperature receptors are unevenly distributed in different areas of the skin. In response to irritation of temperature receptors, the lumen of blood vessels reflexively narrow or expand, as a result of this, heat transfer changes, and the behavior of animals also changes accordingly.

Tactile communication in different taxonomic groups

Although the sense of touch is somewhat limited in its ability to transmit information compared to other senses, in many ways it is the main communication channel for almost all types of living matter that respond to physical contact.

Tactile communication remains important in many vertebrates, in particular birds and mammals, the most social species of which spend a significant part of their time in physical contact with each other. They have an important place in the relationship is the so-called grooming, or caring for feather or coat. It consists in mutual cleaning, licking or simply sorting out feathers or wool. The grooming done by the female during the rearing process and the mutual grooming of the young in the litter plays an important role in their physical and emotional development. Bodily contact between individuals in social species serves as a necessary link in the regulation of relationships between members of the community. So, one of the most effective ways, which are usually resorted to by small songbirds - finches, in order to pacify an aggressive neighbor, is "demonstrating an invitation to clean the feather." With possible aggression of one of the birds directed at another, the object of attack lifts its head high and at the same time puffs up the plumage of the throat or occiput. The reaction of the aggressor is completely unexpected. Instead of attacking a neighbor, he begins to obediently sort out the loose plumage of his throat or nape with his beak. A similar display occurs in some rodents. When two animals that occupy different levels of the hierarchical ladder meet, the subordinate animal allows the dominant to lick its fur. Allowing a high-ranking individual to touch itself, a low-ranking one thereby shows its humility and transfers the potential aggressiveness of the dominant in another direction.

Friendly bodily contact is widespread among highly organized animals. Touch and other tactile signals are widely used in monkey communication. Langurs, baboons, gibbons, and chimpanzees often hug each other in a friendly manner, and a baboon may lightly touch, push, pinch, bite, sniff, or even kiss another baboon as a sign of genuine sympathy. When two chimpanzees meet for the first time, they may gently touch the stranger's head, shoulder, or thigh.

Monkeys constantly sort out wool - they clean each other, which serves as a manifestation of true closeness, intimacy. Grooming is especially important in those groups of primates where social dominance is maintained, such as rhesus monkeys, baboons and gorillas. In such groups, a subordinate individual often communicates, by smacking his lips loudly, that she wants to clean another, occupying a higher position in the social hierarchy. In monkeys, grooming is a typical example of sociosexual contact. Although this kind of relationship often unites animals of the same sex, nevertheless, such contacts are more often observed between females and males, with the former playing an active role, licking and combing the males, while the latter are limited to exposing their partner to certain parts of their bodies. This behavior is not directly related to sexual relationships, although occasionally grooming leads to copulation.

The somatic sensory system provides sensation, which arises from information coming from the body's receptors. These receptors can be divided into the following groups:

Mechanoreceptors, including tactile and proprioceptive;

Thermoreceptors (cold and heat)

Pain receptors that are activated by damaging effects.

Characteristics of tactile receptors. The sensations that arise when these receptors are excited are touch, pressure, vibration, perspiration, itching. Tactile receptors are located in different parts of the skin (epidermis and dermis). Sensation occurs when irritation of the superficial areas of the skin, and pressure - deeper.

Tactile receptors there are 6 types:

1. Free nerve endings - polysensory, which can be excited under the action of both mechanical and thermal influences.

2. Meissner bodies - touch receptors, are encapsulated nerve endings. They quickly adapt. there are many of them on the skin of the fingers, palms, plantar surface.

3. Merkel discs - there are also a lot of them at the fingertips. They, together with Meissner's bodies, are involved in the localization of irritations. They are slowly adapting. Merkel discs are sometimes grouped into domed Pincus-Iggo receptors.

4. Rufin's bodies - branched encapsulated endings of nerve fibers. They are located in the deep layers of the skin, do not adapt well.

5. Pacinian corpuscles - The largest large receptors that are bulb-shaped. They are located more deeply and in fascial tissues (Fig. 12.1). Pacinian corpuscles are irritated by rapid tissue movement, therefore they are important for assessing rapid mechanical effects. Adapt quickly. They are found at the junctions of muscles and tendons in the tissues of the joints, their size is from 0.4 to 0.5 mm.

6. Hair follicle receptors, formed by nerve fibers located at the base of the hair. They quickly adapt.

Characterization of tactile receptors

The sensations that arise when these receptors are excited are touch, pressure, vibration, perspiration, itching. Tactile receptors are located in different parts of the skin (epidermis and dermis). Sensation occurs when irritation of the superficial areas of the skin, and pressure - deep.

All tactile receptors are involved in determining the sensation of tissue vibration. At different vibration frequencies, different receptors are excited. The feeling of tickling and itching is mainly associated with free nerve endings, which quickly adapt. Such receptors are found only in the superficial layers of the skin. Itching is very important for recognizing insects crawling on the skin or a mosquito bite that caused itching.

Tactile Threshold Assessment Frey's esthesiometer is used to determine the force of pressure that occurs on the surface of the skin. The threshold of sensation for different parts of the skin is different and is 50 mg for the most sensitive and 10 g for the least sensitive. Spatial resolution thresholds for tactile sensitivity make it possible to estimate the density of receptors. they are determined using Weber's compass, has two "legs" with needles. Pushing them apart, you can find the minimum distance at which two doti-

Rice. 12.1. Scheme of the structure of skin mechanoreceptors in areas without hair (A) and with hair (B):

1 - stratum corneum, 2 - epidermis, 3 - corium, 4 - subcutaneous tissue, 5 - Meissner's body, 6 - Merkel's disc, 7 - Pacini's body, 8 - hair follicle receptor, 9 - tactile disc, 10 - Rufin's end

ki are perceived separately. This will be spatial discrimination threshold. For the receptors of the skin of the lips, it is 1 mm, for the skin of the fingertips - 2.2 mm, for the skin of the hand - 3.1 mm, for the skin of the forearm - 40.5 mm, and for the skin of the back of the head and back - 54-60 mm , hips - 67.6 mm.

The assessment of tactile sensation is important for the clinic of nervous diseases when making a diagnosis of the impression of various parts of the central nervous system.

proprioceptor characterization

Proprioception provides perception of the posture and movements of our body. It provides deep, kinesthetic sensitivity. Proprioreceptors - mechanoreceptors that are irritated by stretching

Proprioreceptors are divided into 2 groups:

1) muscle spindles;

2) Golgi tendon organs.

muscle spindles are in the muscles. They are attached to the working muscles in parallel, therefore, they are excited either when the extrafusal muscles are stretched, or when the muscle fibers of the spindles, the intrafusal muscles, contract. In this regard, they are called stretch receptors. These receptors are involved in the regulation of muscle length and in assessing the rate of change in muscle length.

Golgi tendon organs located in tendons, ligaments, joints. They are attached from one end to the muscle, and from the other to its tendon, therefore they are located in relation to the muscle in series, but they are also irritated by stretching, which occurs when the working muscle contracts and its tension increases. They are involved in the regulation of muscle tone.

characteristic of thermoreceptors

Thermoreceptors are located not only in the skin, but also in the internal organs and even in the central nervous system (hypothalamus). They are primary receptors, since they are formed by free nerve endings and are divided into cold and heat.

The value of thermoreceptors lies not only in determining the temperature of the environment or objects. They play an important role in regulating the constancy of body temperature in humans and animals. Thermoreceptors are well adapted.

The concept of thermoreceptors is debatable. It is believed that free nerve endings, as well as Ruffini's bodies and Krause's flasks, are thermoreceptors in the skin. There are opinions that instead of the term "thermoreceptors" the concept of "thermal points" should be used, which are selectively sensitive to heat or cold. The lack of consensus is due to the fact that morphologically identifying heat or cold receptors turned out to be quite difficult. Before histological examination, tissues are frozen to make thin layered sections, and it is not possible to establish the type of receptors sensitive to heat or cold. Considering this, it is advisable to use the term "thermosensor", and the question of morphological identification remains for the future.

There is evidence that the number of temperature receptors (points) on human skin is not constant and in the same area varies depending on the temperature of this area and a number of other factors. The lower the temperature of the skin and the environment, the more cold receptors and the less functional activity of thermal ones. At high temperatures, the situation is opposite. The hardening of the body is also important. In adapted people, the number of cold receptors in the cold is less than in non-adapted people.

Wire and cortical sections of the somatic sensory system

From proprioreceptors, impulses go as part of the afferent fibers of the A-alpha group (70-120 m / s), from tactile receptors - as part of the afferent fibers of the A-beta group (40-70 m / s) and A-delta (15-40 m / s), and for impulses coming from receptors that cause itching - as part of c-fibers (0.5-3 m / s). Conduction of impulses from thermoreceptors is carried out by fibers of the A-delta group and C-fibers.

From the trunk and limbs, impulses go as part of the spinal nerves, and from the head - as part of the trigeminal nerve. To conduct impulses that provide tactile sensitivity, the spinal-cortical tracts of Gaulle and Burdakh are used.

Cortical representation of the somatic sensory system located in the postcentral gyrus cm-I (Fig. 12.2).

Cork representation of the somatosensory system is characterized by a number of features.

1. somatotopic organization - a certain arrangement of projections of body parts in it. The body is designed upside down in the postcentral gyrus.

2. The discrepancy between the sizes of these projections: the very territories are occupied by the tongue, lips, larynx, hand, as the most important irritation for evaluation. Small areas - projections of the torso and lower extremities.

3. contralateral location of the projections. From the receptors on the left side, impulses enter the right hemisphere, and from the right side - to the left hemisphere.

4. Consists predominantly of monosensory neurons.

Irritation of the cm-I site leads to sensations identical to those that arise when exposed to stimuli (touch, vibration, heat, cold, rarely pain).

The associative region Cm-II is located at the lateral end of the postcentral gyrus on the upper wall of the Sylvian fissure and consists mainly of polysensory neurons. It has a bilateral somatotopic representation of the body, therefore it plays an essential role in the sensory and motor coordination of the two sides of the body (for example, when both hands are involved).

Damage to the CM-I site leads to a violation of the fine localization of sensations, and damage to the CM-II site leads to astereognosia - unrecognizability of objects during palpation (without vision control).