Tactile sensitivity (Latin tactilis - tangible, from tango - I touch)

a sensation that occurs when various mechanical stimuli act on the skin surface. Including - a type of touch (See Touch) ; depends on the type of impact: touch, pressure, vibration (rhythmic touch). Tactile stimuli are perceived by free nerve endings, nerve plexuses around hair follicles, and Pacinian corpuscles ( rice. 1 And 2 ), Meissner and Merkel discs (see Meissner corpuscles, Merkel cells), etc. Several Merkel discs or Meissner corpuscles can be innervated by one nerve fiber, forming a kind of tactile formation. Encapsulated Receptors (such as Pacinian and Meissner corpuscles) determine the threshold of T. h.: they are excited by touch and vibration and quickly adapt. The sensation of pressure occurs when slowly adapting receptors (such as free nerve endings) are stimulated. Compared to other skin sensations, tactile sensitivity quickly decreases with prolonged irritation, since in general adaptation processes in tactile receptors develop very quickly. The most differentiated T. occurs when the tips of the fingers, lips, and tongue are irritated, where a large number of different mechanoreceptor structures are located. The cortical part of the tactile analyzer a is represented in the postcentral and anterior ectosylvian gyri (see Organs of touch).

Lit.: Ilyinsky O. B., Physiology of skin sensitivity, in the book: Physiology of sensory systems, part 2, L., 1972 (Manual of Physiology); Esakov A. I., Dmitrieva T. M., Neuro-physiological foundations of tactile perception, M., 1971.

O. B. Ilinsky.


Great Soviet Encyclopedia. - M.: Soviet Encyclopedia. 1969-1978 .

See what “Tactile sensitivity” is in other dictionaries:

    TACTIL SENSITIVITY- (English tactile sensitivity) a type of skin sensitivity that is associated with mechanical stimuli. Sensations of touch (see Tangoreceptors), pressure, and partially vibration (see Vibra ...) are associated with T. Great psychological encyclopedia

    - (from lat. tactilis tangible, from tango I touch, I touch), a sensation that occurs when acting on the skin surface of decomposition. mechanical irritants; a type of touch. Tactile receptors are located on the surface of the skin and certain mucous membranes... ... Biological encyclopedic dictionary

    TACTIL SENSITIVITY- (from lat. tactilis touch...) a type of skin sensitivity, which is associated with sensations of touch, pressure and partly vibration. A set of human organs (skin receptors, nerve pathways, corresponding centers in the cortex... ... Encyclopedic Dictionary of Psychology and Pedagogy

    Tactile sensitivity- a type of touch that distinguishes the shape and size of an object, the nature of its surface, associated with the sensation of touching the object. Possible due to the presence of tactile exteroceptors. The largest number of tactile... ... Physical Anthropology. Illustrated explanatory dictionary.

    TACTIL SENSITIVITY- [from lat. tactilis tactile] a type of touch; reflection in consciousness of certain mechanical properties of an object acting on the corresponding receptors of the skin surface as one of the types of irritations of touch, pressure,... ... Psychomotorics: dictionary-reference book

    Tactile sensitivity- A type of skin sensitivity associated with sensations of touch, pressure and partly vibration... Adaptive physical culture. Concise encyclopedic dictionary- SENSITIVITY, the ability of animals and humans to perceive irritations from the external environment and from their own tissues and organs. In animals with a nervous system, specialized sensory cells (receptors) have a highly selective... ... Modern encyclopedia

    Sensitivity is the body’s ability to perceive irritations emanating from the environment or from its own tissues and organs, and respond to them with differentiated forms of reactions. Types of sensitivity General sensitivity Superficial... ... Wikipedia


Skin receptors are responsible for our ability to sense touch, heat, cold and pain. Receptors are modified nerve endings that can be either free, unspecialized 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 interact effectively and safely with the external environment.

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 Pacinian, Meissner, Merkel and Ruffini corpuscles. 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 Pacinian receptors in these areas.

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

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

Skin receptors responsible for tactile sensitivity

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

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

Skin receptors that respond to temperature changes

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 hot. Other theories of thermoreception claim that it is free nerve endings that are designed to sense temperature. In this case, thermal stimulation is analyzed by deep nerve fibers, and cold stimulation by superficial ones. Between themselves, 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 located in the skin are responsible for the perception of pain.

Prolonged and severe painful 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.

Meissner's corpuscles located in the superficial layers of the skin (dermis) of the lips and the oral mucosa itself, respond to touch. When mechanical stimulation increases, they become excited Merkel wheels, which are localized in the deep layers of the skin epidermis and mucous epithelium. Sensations of pressure and vibration occur when irritated Pacinian corpuscle located in the subcutaneous tissue and submucosal layer. Due to the deep location of Pacinian corpuscles, local application of anesthesia to the superficial layers of the mucous membrane and skin does not eliminate the sensation of pressure and vibration, which the patient must be warned about before surgery in these conditions.

From most tactile mechanoreceptors of the oral region, sensory signals enter the central nervous system along myelinated Ab nerve fibers at a speed of 30-70 m/s. The central section of the tactile sensory system is located in the posterior central gyrus of the cerebral cortex.

Tactile sensations can be caused by irritation of only certain areas of the skin and mucous membranes, which are called sensitive tactile points . The spatial threshold of tactile sensitivity is inversely proportional to the number of receptors per unit area and directly proportional to the distance between the receptors. The spatial threshold of tactile sensations on the tips of the fingers, tongue and lips is significantly lower (1-3 mm) than on other parts of the body (50-100 mm). This is due to the difference in the density of receptors per unit surface area.

The most dense tactile receptors are located on the tip of the tongue, the mucous membrane and the red border of the lips, which is necessary for testing food for edibility. The upper lip is most sensitive to mechanical irritation. The mucous membrane of the hard palate has a relatively high level of tactile sensitivity, which ensures the formation of a food bolus during chewing. The mucous membrane of the vestibular surface of the gums has the least tactile sensitivity. At the same time, in the area of ​​gingival papillae there is a decreasing gradient of sensitivity from the incisors to the molars.

A method for studying absolute or spatial thresholds of tactile sensitivity is called esthesiometry . The study of tactile perception by the oral mucosa makes it possible to predict individual characteristics of adaptation to removable dentures in patients with partial or complete edentia. The prosthesis is a foreign body that irritates tactile receptors, which leads to reflex hypersalivation, the occurrence of a gag reflex, and impaired coordination of chewing, swallowing and speech. However, most tactile receptors are fast-adapting. In this regard, and also due to the absence of non-adaptive tactile receptors, significant problems with getting used to dentures, as a rule, do not arise. In this case, along with the adaptation of the receptor apparatus, adaptation of the conductive and central sections of the analyzer occurs. This is the result of the high plasticity of the nerve centers, which ensure rapid adaptation of the functions of chewing, swallowing and speech to new conditions. The denture ceases to feel like a foreign body, chewing efficiency is restored, the gag reflex fades, salivation, swallowing and speech are normalized.


Temperature reception in the oral region provides the perception of thermal stimuli - heat and cold. Thermoreceptors that perceive cold are histologically represented by Krause flasks, located in the epidermis of the red border of the lips and the epithelium of the oral mucosa. Thermal receptors - Ruffini bodies - are localized deeper - in the actual dermal layer of the lips and in the actual mucous membrane of the mouth. Thin myelinated fibers of type Ad with an excitation speed of 5-15 m/s depart from cold receptors, and non-myelinated fibers of type C (0.5-3 m/s) depart from heat receptors. The central section of the temperature sensory system is located in the posterior central gyrus of the cerebral cortex.

As a rule, heat and cold receptors are excited by stimuli of appropriate quality. However, under certain conditions, cold receptors can perceive thermal stimuli at temperatures above 45 0 C (for example, when immersed in a hot bath). Depending on the initial conditions, the same temperature can cause both a feeling of warmth and a feeling of cold.

The predominance of thermoreceptors in the skin and mucous membranes that respond to cold stimuli (10:1), and the deep location of thermal receptors, cause higher sensitivity to cold. In this case, cold sensitivity decreases from the anterior to posterior parts of the mouth, and thermal sensitivity, on the contrary, increases. The tip of the tongue and the red border of the lips are most sensitive to temperature irritations, which ensures testing of the suitability of the food consumed. The mucous membrane of the cheeks is insensitive to cold and heat. The perception of heat in the center of the hard palate is completely absent, and the central part of the back surface of the tongue does not perceive either thermal or cold influences.

Receptors in dentin and dental pulp have the ability to perceive temperature. The threshold of cold sensitivity for incisors is on average 20 0 C, and for canines, premolars and molars - 11-13 0 C. The threshold of thermal sensitivity for incisors is a temperature of about 52 0 C, for other teeth - 60-70 0 C.

The study of temperature sensitivity by determining heat or cold thresholds is called thermoesthesiometry . To study the temperature sensitivity of teeth, they are irrigated with hot or, more often, cold water or a cotton swab soaked in ether is used, which, evaporating, cools the tooth. If temperature stimuli cause adequate sensations of heat or cold, this indicates the normal condition of the dental tissues. With caries, cold irritation causes pain. With pulpitis, pain is caused by thermal stimuli, and cold stimuli, on the contrary, reduce it. A pulpless tooth does not react to either cold or heat.

Tactile and temperature sensitivity of the mouth is complemented muscle-articular reception, which provides a sense of the spatial position of the lower jaw relative to the upper jaw, the sensation of its movement, and the perception of contractile force of the muscles. This type of sensitivity is provided proprioceptors, which are localized in intrafusal muscle fibers, temporomandibular joints, in the ligamentous apparatus of masticatory and facial muscles. Sensory signals from proprioceptors enter the central nervous system mainly through thick myelinated nerve fibers of type Aa at a speed of 70-120 m/s. The central section of the proprioceptive sensory system is located in the posterior central gyrus of the cerebral cortex.

The most important sensory function of the oral region is pain reception, which provides the perception of stimuli that can lead to damage or destroy body tissue. Unlike all other types of sensory modalities, pain perception does not have an adequate stimulus. Almost any super-strong stimulus can cause pain.

Pain is a universal unpleasant sensory sensation and emotional experience associated with the threat of destruction or tissue damage that has already occurred.

According to biological significance, two types of pain are distinguished: physiological And pathological. The main tasks of physiological pain:

1) informing the body about any form of threat to its existence or integrity,

2) participation in the organization of adaptive behavior aimed at preventing the spread and eliminating damage or eliminating its threat.

Pain ensures the mobilization of most body systems to protect against tissue damage and is accompanied by the deployment of defensive behavior. Depending on the situation, the sensation of pain and the accompanying behavioral and reflexive reactions can be consciously suppressed. However, humoral as well as vegetative changes persist in any case, which is an inevitable sign of tissue damage. Therefore, when relieving pain syndromes, it is advisable to use medications that can stabilize the physiological functions of the body.

After the organization of protective behavior, pain loses its adaptive functions and acquires the significance of an independent pathogenetic factor. For many diseases, pain is one of the first, and sometimes the only manifestation of pathology and the main diagnostic indicator.

Based on the location of the damaging factor, two types of pain are distinguished: somatic And visceral. Somatic pain is associated with extreme external influences, while visceral pain is caused by internal pathological processes.

Somatic pain is divided into two types: primary And secondary. Primary (epicritic )pain manifests itself immediately after damage, is quickly recognized, easily determined by quality and localization, disappears after the cessation of harmful stimulation, and is accompanied by adaptation. Secondary (protopathic )pain manifests itself 0.5-1 s after the initial sensation, is slowly realized, is poorly determined in quality and localization, persists for a long time after the cessation of stimulation, and is not accompanied by adaptation.

Currently, there are three main theories of the mechanisms of pain perception:

1) intensity theory,

2) theory of specificity,

3) theory of impulse distribution.

According to the intensity theory, superstrong stimulation of receptors, regardless of their modality, causes high-amplitude RP and high-frequency discharge activity of sensory neurons, which is transformed by the central nervous system into the sensation of pain (amplitude-frequency coding).

According to the theory of impulse distribution, damaging stimuli cause a special order (pattern) of afferent impulses, which differs from discharge activity caused by factors indifferent to the body (pulse interval coding). In this case, the central nervous system converts the incoming afferent flow into a sensation of pain.

In contrast, the specificity theory assumes (by analogy with other sensory systems) the existence of special receptors and afferents that respond with excitation only to stimuli of such intensity that can damage tissue (binary and spatial coding).

Thus, an irritant can cause a sensation of pain only if, under its influence, a special, algogenic signaling- a flow of afferent excitations, in which, according to the amplitude-frequency-spatial principle, information about the threat of destruction or damage to the body’s tissues has already occurred is encoded.

The sensory system that provides the perception of harmful stimuli is called nociceptive . The receptors of this system are nociceptors, are divided into four types:

1) mechanosensitive, which are excited as a result of mechanical displacement of the receptor membrane,

2) chemosensitive, reacting to chemicals released by damaged cells (acetylcholine, histamine, serotonin, prostaglandins),

3) thermosensitive, which are activated under the influence of thermal stimuli outside the physiological range,

4) multimodal, responding both to chemicals and to intense mechanical and thermal stimuli.

Nociceptors are non-adaptive, high-threshold receptors. In the skin of the face and oral mucosa, as well as periodontium, pulp and dentin of teeth, they are predominantly represented by free nerve endings.

The mucous membrane of the vestibular surface of the lower jaw in the area of ​​the lateral incisors is characterized by pronounced pain sensitivity. The lingual surface of the gum mucosa is characterized by the least pain sensitivity. On the inner surface of the cheek in the area of ​​the upper molars there is a narrow section of mucous membrane, absolutely devoid of pain sensitivity.

An exceptionally strong pain sensation occurs even with a light touch of the tooth pulp, which is due to the high density of highly sensitive nerve endings and fibers that penetrate the dentin right up to the enamel-dentin border. There are 15,000-30,000 pain receptors per 1 cm 2 of dentin; at the border of enamel and dentin, the number of nociceptors reaches 75,000, while in the skin their number does not exceed 200. All this is the reason for the particular severity of pain that occurs under the influence of temperature, chemical and mechanical stimuli in case of damage and destruction of dental tissue, including during their treatment.

Sensory signals from the nociceptors of the oral region enter the central nervous system through myelinated nerve fibers of types Ab and Ad, as well as through unmyelinated fibers of group C, most of which pass through the second and third branches of the trigeminal nerve. Information from nociceptors about the dysfunction of the oral tissues comes to posterior central gyrus and to the medial sections orbital cortex cerebral hemispheres.

The close relationship between the various nuclei of the trigeminal nerve and their interaction with the nuclei of the reticular formation causes a wide irradiation of excitation, making it difficult to localize toothache and its reflection (projection) to fairly distant areas of the face, head and neck.

Sometimes after surgery to remove the affected tooth, a feeling of pain persists, which is called phantom . Phantom pain is caused by the fact that nociceptive afferentation from the affected tooth preceding removal causes neurogenic (central ) sensitization - increased sensitivity associated with increased excitability in the conduction and central parts of the nociceptive system. Additional irritation during surgery causes the appearance of persistent pathologically enhanced foci of excitation circulation in the central nervous system, which is perceived by the cells of the cerebral cortex as prolonged, often continuous pain. Local therapeutic measures do not lead to a reduction or cessation of such pain, since their source lies in the structures of the central nervous system, which should be influenced by activating the antinociceptive system of the brain.

The main functions of the endogenous antinociceptive system are limiting the level of pain excitation, as well as regulating and maintaining the threshold of pain sensitivity. This is ensured through the mechanisms of presynaptic and postsynaptic inhibition of nociceptive neurons at all levels of the central nervous system. Opiate, adrenergic, dopaminergic and serotonergic brain structures participate in the implementation of the influence of the antinociceptive system. The production of opiate morphine-like compounds - endorphins, enkephalins and dinarphins - is of key importance.

The pain threshold is the result of the interaction of the nociceptive and antinociceptive systems, which are in a state of constant tonic activity. Elimination of the constant inhibitory influence of the antinociceptive system can lead to a condition hyperalgia or even the occurrence of spontaneous pain. An increase in tonic activity of the antinociceptive system leads to the development of congenital analgia- insensitivity to pain.

Fear, suppressing the activity of the antinociceptive system, sharply increases the reaction to pain, reduces the threshold of pain sensitivity, and states such as aggression-rage, on the contrary, increase it. Overestimation of pain intensity may be associated with preparation and anticipation of medical procedures. However, pain sensitivity decreases when a person is warned in advance about the nature of the upcoming impact. Explanation or distracting conversations before surgery significantly reduce pain and reduce the need for painkillers.

A specific feature of the sensory function of the oral region is taste sensitivity.

Taste– a sensation resulting from the perception of the four elementary taste qualities of chemical substances dissolved in the oral fluid – sweet, bitter, sour And salty.

A sensory system that carries out contact perception and assessment of the taste properties of chemicals acting on organ of taste, called taste analyzer .

Human taste organ presented taste buds which are localized mainly in papillae of the tongue: mushroom-shaped, leaf-shaped And trough-shaped. Mushroom-shaped papillae are located mainly on the mucous membrane of the tip of the tongue, leaf-shaped papillae are located along the lateral surface of the posterior parts of the tongue, and groove-shaped papillae are located across the back, at the root of the tongue. Separate taste buds are present on the soft and hard palate, the posterior wall of the pharynx, tonsils, epiglottis and larynx.

Structural and functional characteristics of the skin analyzer

Connection of cutaneous and visceral pathways in:
1 - Gaulle beam;
2 - Burdach beam;
3 - posterior root;
4 - anterior root;
5 - spinothalamic tract (conducting pain sensitivity);
6 - motor axons;
7 - sympathetic axons;
8 - front horn;
9 - propriospinal tract;
10 - posterior horn;
11 - visceroreceptors;
12 - proprioceptors;
13 - thermoreceptors;
14 - nociceptors;
15 - mechanoreceptors

Its peripheral part is located in the skin. These are pain, tactile and temperature receptors. There are about a million pain receptors. When excited, they create a sensation that triggers the body's defenses.

Touch receptors produce sensations of pressure and contact. These receptors play a significant role in cognition of the surrounding world. With our help, we determine not only whether objects have a smooth or rough surface, but also their size, and sometimes their shape.

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

The skin of the face and abdomen is most sensitive to the effects of temperature irritants. The skin of the feet, compared to the skin of the face, is two times less sensitive to cold and four times less sensitive to heat. Temperatures help to feel the structure of a combination of movements and speed. This happens because when the position of parts of the body quickly changes or the speed of movement is high, 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 nerve fibers of the spinal nerves and the trigeminal nerve; the central departments are mainly in, and the cortical representation is projected into the postcentral.

The skin provides tactile, temperature and pain perception. Per 1 cm2 of skin, on average, there are 12-13 cold points, 1-2 heat 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 hairless skin, as well as on the mucous membranes, special receptor cells (Meissner bodies) located in the papillary layer of the skin react to touch. On skin covered with hair, hair follicle receptors with 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 slow adapting receptors. Adequate for them is the flexion of the epidermis under the action of a mechanical stimulus on the skin. Vibration is sensed by Pacinian corpuscles, located both in the mucous and non-hairy parts of the skin, in the adipose tissue of the subcutaneous layers, as well as in the joint capsules and tendons. Pacinian corpuscles have very rapid adaptation and respond to acceleration when the skin is displaced as a result of mechanical stimuli; several Pacinian 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 body; 4 - hair follicle receptor; 5 - tactile disk (Pincus-Iggo body); 6 - ending 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, per 1 square centimeter of skin surface there are 50 pain, 25 tactile, 12 cold and 2 heat points. Skin receptors are localized at different depths, for example, cold receptors are located closer to the surface of the skin (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 modalities. The occurrence of various sensations depends not only on which receptor formation of the skin has been irritated, but also on the nature of the impulse coming from this receptor to the skin.

The sense of touch (touch) occurs when light pressure is applied to 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 areas of the skin. An additional receptor for touch is the nerve fibers that weave around the hair follicle (the so-called hair sensitivity). The feeling of deep pressure is perceived by the lamellar corpuscles.

Pain is perceived mainly by free nerve endings located in both the epidermis and 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 sense, the perception of heat and cold, is of great importance for reflex processes that regulate body temperature. It is assumed that thermal stimuli are perceived by Ruffini's corpuscles, and cold stimuli by Krause's end flasks. There are significantly more cold spots on the entire surface of the skin than heat spots.

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.

Schematic section 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 - skin 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, 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 and release carbon dioxide, which increases with increasing ambient temperature, during physical work, during digestion, and the development of inflammatory processes in the skin.

The somatic sensory system provides sensations that arise from information received from receptors in the body. 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 stimuli.

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

Tactile receptors There are 6 types:

1. Free nerve endings - polysensory, which can be excited by both mechanical and temperature influences.

2. Meissner's corpuscles - touch receptors, are encapsulated nerve endings. They adapt quickly. there are many of them on the skin of the fingers, palms, and plantar surfaces.

3. Merkel discs - there are also many of them on the tips of the fingers. They, together with Meissner's corpuscles, participate in the localization of irritations. They are slow to adapt. Merkel discs are sometimes grouped into dome-shaped Pincus-Iggo receptors.

4. Rufin corpuscles are branched encapsulated endings of nerve fibers. They are located in the deep layers of the skin and do not adapt well.

5. Pacinian corpuscles - The largest large receptors that have the shape of an onion. They are located more deeply and in the fascial tissues (Fig. 12.1). Pacinian corpuscles are irritated by rapid tissue movement and are therefore important for assessing rapid mechanical stress. Adapt quickly. They are found at the junction 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 adapt quickly.

Characteristics of tactile receptors

The sensations that arise when these receptors are stimulated are touch, pressure, vibration, tickling, itching. Tactile receptors are located in different parts of the skin (epidermis and dermis). The sensation occurs when superficial areas of the skin are irritated, and pressure occurs in deep areas.

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

Assessment of tactile sensation thresholds occurs using a Frey esthesiometer, which allows you to determine the force of pressure occurring on the surface of the skin. The sensation threshold for different areas 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 allow us to estimate the density of receptors. they are determined using a Weber compass; it has two “legs” with needles. By moving them apart, you can find the minimum distance at which two

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 corpuscle, 6 - Merkel's disk, 7 - Pacinian's corpuscle, 8 - hair follicle receptor, 9 - tactile disk, 10 - ending of Rufin

ki are perceived separately. This is what will happen spatial discrimination threshold. For the skin receptors 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 and neck - 54-60 mm , hips - 67.6 mm.

Assessment of tactile sensation is important for the clinic of nervous diseases when diagnosing the impression of various parts of the central nervous system.

characteristics of proprioceptors

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

Proprioceptors are divided into 2 groups:

1) muscle spindles;

2) Golgi tendon organs.

Muscle spindles are located in the muscles. They are attached in parallel to the working muscles, therefore they are excited either by stretching of the extrafusal muscles, or by contraction of the muscle fibers of the spindles - intrafusal muscles. For this reason, they are called stretch receptors. These receptors are involved in the regulation of muscle length and in estimating the rate of change in muscle length.

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

characteristics of thermoreceptors

Thermoreceptors are located not only in the skin, but also in 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 importance of thermoreceptors lies not only in determining the temperature of the environment or objects. They play a big role in regulating the constancy of body temperature in humans and animals. Thermoreceptors adapt well.

The concept of thermoreceptors is controversial. It is believed that thermoreceptors in the skin are free nerve endings, as well as Ruffini corpuscles and Krause flasks. 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 has proven to be quite difficult. Before histological examination, tissues are frozen to make thin slices, and it is not possible to determine the type of receptors sensitive to heat or cold. Taking this into account, 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 changes 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. Hardening the body is also important. In adapted people, the number of cold receptors in the cold is less than in non-adapted people.

Wired and cortical sections of the somatic sensory system

From proprioceptors, impulses come as part of afferent fibers of the A-alpha group (70-120 m/s), from tactile receptors - as part of 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 - in the composition of c-fibers (0.5-3 m / s). The conduction of impulses from thermoreceptors is carried out by A-delta fibers and C-fibers.

From the torso and limbs, impulses come 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 Burdach are used.

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

The 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 projected upside down in the postcentral gyrus.

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

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

4. Consists primarily of monosensory neurons.

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

The associative area Cm-II is located at the lateral end of the postcentral gyrus on the superior wall of the Sylvian fissure and consists primarily of polysensory neurons. It has a bilateral somatotopic representation of the body, and therefore plays a significant role in sensory and motor coordination of two sides of the body (for example, when operating both hands).

Damage to the cm-I area leads to disruption of the fine localization of sensations, and damage to the cm-II area leads to astereognosia - unrecognizability of objects when palpated (without vision control).