Sensitivity I

the ability of the organism to perceive various stimuli emanating from the external and internal environment, and to respond to them.

Ch. is based on the processes of reception, the biological significance of which lies in the perception of stimuli acting on them, their transformation into excitation processes (Excitation) , which are the source of the corresponding sensations (pain, temperature, light, auditory, etc.). Subjectively experienced appears with threshold stimulation of certain receptors (Receptors) . In those cases when the incoming receptors in the c.n.s. below the threshold of sensation, it does not cause this or that sensation, however, it can lead to certain reflex reactions of the body (vegetative-vascular, etc.).

For understanding the physiological mechanisms of Ch., the teachings of I.P. Pavlova about analyzers (Analyzers) . As a result of the activity of all links of the analyzer, a subtle and synthesis of stimuli acting on irritations is carried out. In this case, not only the transmission of impulses from the receptors to the central analyzer occurs, but also difficult process reverse (efferent) regulation of sensitive perception (see Self-regulation of physiological functions) . The excitability of the receptor apparatus is determined both by the absolute intensity of stimulation, and by the number of simultaneously stimulated receptors or by the quality of their repeated irritations - the law of summation of receptor irritations. the excitability of the receptor depends on the influence of the central nervous system. and sympathetic innervation.

Sensory impulses from the peripheral receptor apparatus reach the cerebral cortex along specific pathways and nonspecific pathways. reticular formation(Reticular formation) Non-specific afferent impulses pass along the spinoreticular pathway, which at the level of the brainstem (Brain Stem) has connections with the cells of the reticular formation. The activating and inhibitory systems of the reticular formation (see Functional systems) carry out the regulation of afferent impulses, participate in the selection of information coming from the periphery to the higher parts of the Ch. system, passing some impulses and blocking others.

There are general and special Ch. General Ch. is divided into exteroceptive, proprioceptive and interoceptive. Exteroceptive (superficial, skin) include pain, temperature (thermal and cold) and tactile Ch. () with their varieties (for example, electrocutaneous - sensations caused by various types electric current; feeling of humidity - hygroesthesia , It is based on a combination tactile sensation with temperature; a feeling of itching is a variant of tactile Ch., etc.).

Proprioceptive (deep) Ch. - bathiesthesia includes muscular-articular Ch. (a sense of the position of the body and its parts in space), vibration (), pressure (). To interoceptive (vegetative-visceral) is Ch., associated with the receptor apparatus in the internal organs and blood vessels. Allocate also complex types sensitivity: two-dimensional-spatial sense, localization, discriminatory Ch., stereognosis, etc.

The English neurologist Ged (N. Head) proposed to divide the general sensitivity into protopathic and epicritical. Protopathic Ch. is phylogenetically older, associated with the thalamus, and serves to perceive nociceptive stimuli that threaten the body with tissue destruction or even death (for example, strong pain stimuli, sudden temperature effects, etc.). Epicritical Ch., phylogenetically younger, is not associated with the perception of damaging effects. It enables the body to navigate in the environment, to perceive weak stimuli, to which the body can respond with a choice reaction (an arbitrary motor act). Epicritical Ch. include tactile, low temperature fluctuations (from 27 to 35 °), irritation, their difference (discrimination), and muscular-articular feeling. Decrease or function of the epicritical Ch. leads to disinhibition of the function of the protopathic Ch. system and makes the perception of nociceptive irritations unusually strong. At the same time, pain and temperature stimuli are perceived as especially unpleasant, they become more diffuse, spilled and do not lend themselves to precise localization, which is indicated by the term "".

Special Ch. is associated with the function of the sense organs. It includes Vision , Hearing , Smell , Taste , Body balance . Taste Ch. is associated with contact receptors, other types - with distant receptors.

Ch.'s differentiation is connected with structural and physiological features of a peripheral sensitive neuron - its receptor and a dendrite. Normal for 1 cm 2 skin has an average of 100-200 pain, 20-25 tactile, 12-15 cold and 1-2 heat receptors. Peripheral sensitive nerve fibers(dendrites of the cells of the spinal node, trigeminal node, jugular node, etc.) conduct excitation impulses with different speed depending on the thickness of their myelin layer. Group A fibers, covered with a thick layer of myelin, conduct an impulse at a speed of 12-120 m/s; group B fibers, which have a thin myelin layer, drive impulses at a speed of 3-14 m/s; group C fibers - unmyelinated (have only one) - at a speed of 1-2 m/s. Group A fibers serve to conduct impulses of tactile and deep Ch., but they can also conduct pain stimuli. Group B fibers conduct pain and tactile stimuli. Group C fibers are conductors of mainly pain stimuli.

The bodies of the first neurons of all types of Ch. are located in the spinal ganglia ( rice. one ) and in the nodes of sensory cranial nerves (Cranial nerves) . The axons of these neurons, as part of the posterior roots of the spinal nerves and the sensory roots of the corresponding cranial nerves, also enter the brain stem, forming two groups of fibers. Short fibers terminate in a synapse at the cells of the posterior horn spinal cord(their analogue in the brainstem is the descending spinal tract of the trigeminal nerve), which are the second sensitive neuron. The axons of most of these neurons, having risen by 2-3 segments, pass through the anterior white commissure to the opposite side of the spinal cord and go up as part of the lateral spinothalamic tract, ending in a synapse at cells of specific ventrolateral nuclei of the thalamus. These fibers carry pain and temperature pulses. Another part of the fibers of the spinothalamic pathway, passing through the simplest types of tactile sensitivity (, hair sensitivity, etc.), is located in the anterior funiculus of the spinal cord and makes up the anterior spinothalamic tract, which also reaches the thalamus. cells of the nuclei of the thalamus (third sensory neurons) axons, forming the posterior third of the posterior thigh internal capsule, reach the sensory neurons of the cortex big brain(Cerebral cortex) (posterior central and parietal).

A group of long fibers from the posterior root passes uninterruptedly in the same direction, forming thin and wedge-shaped bundles. As part of these bundles, axons, without crossing, rise to the medulla oblongata, where they end in nuclei of the same name - in the thin and wedge-shaped nuclei. Thin (Goll) contains fibers that conduct Ch. from lower half body, wedge-shaped (Burdaha) - from the upper half of the body. The axons of the cells of the thin and sphenoid nuclei pass at the level of the medulla oblongata to opposite side- upper sensitive medial loops. After this decussation in the suture, the fibers of the medial loop go up in the posterior part (tire) of the pons and midbrain and, together with the fibers of the spinothalamic tract, approach the ventrolateral nucleus of the thalamus. Fibers from the thin nucleus approach the cells located laterally, and from the sphenoid nucleus - to more medial groups of cells. The axons of sensitive cells of the nuclei of the trigeminal nerve also fit here. neurons of the thalamic nuclei, axons pass through the posterior third of the posterior thigh of the internal capsule and, ending at the cells of the cortex of the postcentral gyrus (fields 1, 2, 3), the upper parietal lobule (fields 5 and 7) of the cerebral hemispheres. These long fibers carry out muscular-articular, vibrational, complex types of tactile, two-dimensional-spatial, discriminatory Ch., feelings of pressure, stereognosis - from the receptors of the same half of the body to the medulla oblongata. Above the medulla oblongata, they reconnect with conductors of pain and temperature sensitivity of the corresponding side of the body.

Research methods sensitivity is divided into subjective and objective. Subjective Methods are based on the psychophysiological study of sensation (absolute and differential thresholds of Ch.). Clinical Study H. (see Examination of the patient , neurological examination) should be carried out in a warm and quiet room. In order to better focus on the perception and analysis of sensations, he should lie with his eyes closed. The results of Ch.'s research depend on the patient's reaction, his attention, the safety of consciousness, etc.

Pain sensitivity is examined by a pin prick or other sharp object; temperature - by touching the skin with test tubes filled with cool (not higher than 25 °) and hot (40-50 °) water. More accurately, temperature Ch. can be examined using a thermoesthesiometer, and pain - with a Rudzit algesimeter. The threshold characteristic of pain and tactile sensitivity can be obtained by examining graduated bristles and hairs using the Frey method. Tactile Ch. is examined by lightly touching the skin with a brush, pieces of cotton wool, soft paper, etc. Discriminatory Ch. is examined with Weber's compass. Normally, two separate irritations on the palmar surface of the fingers are perceived when one is removed from the other by 2 mm, on the palmar surface of the hand, this distance reaches 6-10 mm, on the forearm and dorsum of the foot - 40 mm, and on the back and hips - 65-67 mm.

The muscular-articular feeling is examined in the position of the patient lying down, always with his eyes closed. produces an unsharp passive in individual small or large joints - extension, adduction, etc. The subject must determine the direction, volume and these movements. You can use a kinesthesiometer. With a pronounced violation of the muscular-articular feeling, a sensitive (Ataxia) .

The feeling of pressure is determined by distinguishing pressure from a light touch, and also by detecting the difference in the degree of pressure applied. The study is performed using a baresthesiometer - a spring apparatus with a pressure intensity scale expressed in grams. Normally, it distinguishes between an increase or decrease in pressure on the arm by 1/10 - 1/20 of the original pressure.

Vibrating frequency is examined with a tuning fork 64-128 Hz. The leg of a sounding tuning fork is placed on protrusions (ankles, forearms, iliac crest, etc.). Normal vibration at the ankles lasts 8-10 With, on the forearm - 11-12 With.

The ability to recognize two-dimensional stimuli is examined by asking the patient to determine, with his eyes closed, the numbers, letters and figures that he draws with a pencil or the blunt end of a pin on the skin of the subject.

The stereognostic sense is defined by the ability to recognize coins, a pencil, a key, etc. when touched with closed eyes. The subject evaluates the shape, consistency, temperature, surfaces, approximate mass and other qualities of the object. The complex act of stereognosis is associated with the associative activity of the brain. When defeated general types sensitivity is impossible - secondary (pseudoastereognosis). Primary happens with a disorder of higher brain (cortical) functions - gnosis (see Agnosia) .

Sensitivity disorders often seen with various diseases nervous system and, as a rule, are used to clarify the tonic diagnosis, as well as to control the dynamics of the pathological process under the influence of the patient's treatment. Distinguish between quantitative and qualitative violations of Ch. Quantitative are a decrease in the intensity of sensation - or a complete loss of Ch. -. This applies to all types of Ch., analgesia - a decrease or absence of pain Ch., thermoanesthesia - a decrease or absence of temperature Ch., topohypesthesia, topanesthesia - a decrease or loss of localization of irritations, etc. An increase in Ch. - is associated with a decrease in the threshold of perception of one or another irritation . Qualitative disturbances of Ch. include a perversion of the perception of external stimuli, for example: the occurrence of a sensation of pain during cold or thermal irritation, a sensation of a larger size of a palpated object - macroesthesia, a sensation of many objects instead of one - polyesthesia, a sensation of pain in another zone in relation to the injection site - synalgia, sensation of irritation not in the place of its application - alloesthesia, sensation of irritation in a symmetrical area on the other hand -, inadequate perception of various irritations -. special shape Ch. represents a qualitative change - a kind of painful perception of various sharp irritations. With hyperpathy, excitability increases (light irritations are perceived in the hyperpathic zone less clearly than normal, and intense irritations are sharply painful, extremely unpleasant, painful), irritations are poorly localized by the patient, and they are noted for a long time.

Ch.'s disorders include paresthesias - various sensations not associated with any external influence - goosebumps, numbness, tingling, stiffness of skin areas, pain in the hair roots (trichalgia), a feeling of skin moisture, drops of liquid on it (). Especially often, a variety of paresthesias are observed with dorsal tabes (Tapes dorsalis) , funicular myelosis (Funicular myelosis) and other diseases of the nervous system, in which the posterior cords of the spinal cord and posterior roots are involved in the process.

Depending on the localization of the pathological process in the nervous system, there are different types disorders Ch. When the receptor apparatus is affected, local damage is observed due to a decrease in the number of receptor points, as well as changes in the threshold characteristics of different types of Ch. (an increase or decrease in the threshold for pain, tactile, and other types of Ch.).

When a sensory nerve is damaged, two zones of disturbance are detected: anesthesia in the zone of autonomic innervation of this nerve and hypesthesia with hyperpathy in the zone of mixed innervation (overlapping zones of innervation with another nerve). Mismatch of violation zones is noted various kinds Ch.: largest surface occupies an area with a violation of temperature Ch., then tactile, and least of all - a site of violation of pain Ch. When the function of the damaged nerve is restored, there is certain sequence return of sensitivity: first, the protopathic Ch. is restored, it becomes possible to distinguish relatively high temperature(above 37°) and low (below 20°), injections are perceived as extremely unpleasant, diffuse, long-lasting sensations. Later (about 1 year later), tactile sensitivity is restored, the ability to distinguish between temperatures from 26 to 37 °, at the same time, the localization error and increased pain stimuli disappear (Ged-Sherren's law). With damage to the peripheral nerve, all types of sensitivity are disturbed (see Neuritis) . For multiple symmetrical lesions peripheral nerves limbs (see Polyneuropathies) characteristic is a violation of all types of Ch. according to the polyneuritic or distal type - in the form of gloves on the hands and stockings (socks) on the legs ( rice. 2 ).

With damage to the posterior roots, disorders of all types of Ch. are localized in the corresponding dermatome ( rice. 3 ). With a viral lesion of the spinal node and sensitive root, paresthesia and hypesthesia are combined with herpetic eruptions in the same dermatome (see Ganglionitis) .

With the defeat of the entire diameter of the spinal cord, a conductor of all types develops with an upper border, which indicates the level of the spinal cord ( rice. four ). With the localization of the pathological focus above the cervical thickening of the spinal cord, the upper and lower extremities, the trunk appear. This is combined with central tetraparesis, dysfunction of the pelvic organs (see spinal cord) . The pathological focus at the level of the upper thoracic segments is manifested by anesthesia on the lower extremities, central lower paraparesis, and dysfunction of the pelvic organs. When the lumbar segments of the spinal cord are affected, conduction anesthesia captures the lower limbs and the anogenital zone.

The pathology of the thalamus causes Dejerine-Roussy, in which all types of Ch. decrease or disappear on the half of the body opposite to the focus, sensitive and moderate develop in the same limbs, contralateral hemianopsia . Characteristic of the defeat of the thalamus is hyperpathy and central against the background of hypesthesia on the entire half of the body. Thalamic pain is always very intense, diffuse, burning and resistant to analgesics.

With the defeat of the posterior thigh of the internal capsule, the so-called capsular one develops on the half of the body opposite to the focus. It is characterized by more pronounced Ch.'s disorders in the distal extremities, especially on the arm.

A pathological focus in the radiant crown or cerebral cortex ( postcentral) causes monoanesthesia on the face or only on the arm, or only on the leg (depending on the location of the focus and in accordance with the somatotopic representation of sensitivity). with cortical pathological foci, it is more pronounced in the distal parts of the limb, and the muscular-articular feeling and vibrational frequency are more disturbed than the superficial frequency.

When the pathological process is localized in the parasagittal region, both paracentral lobules are simultaneously disturbed and sensitivity is impaired on both feet.

Irritation of the sensitive zone of the cerebral cortex (with, cicatricial adhesive process, etc.) leads to Jacksonian sensitive seizures (see Jacksonian epilepsy) : paresthesias in the face, arm or leg, lasting from a few seconds to minutes without a change in consciousness. With damage to the parietal lobe, more complex types of Ch.'s disturbance develop, a weakening of the ability to discriminate, two-dimensional-spatial Ch., stereognosis, and to determine spatial relationships (topognosis).

Bibliography: Krol M.B. and Fedorova E.A. The main neuropathological syndromes, M,. 1966; Skoromets A.A. diseases of the nervous system, L., 1989.

Rice. 4. Scheme of conduction spinal paraanesthesia with an upper limit on Th X .

Rice. 1. Scheme of conductors of superficial (A) and deep (B) sensitivity: 1 - cell of the spinal ganglion; 2 - cell of the posterior horn of the spinal cord; 3 - spinothalamic tract; four - ; 5 - postcentral gyrus (zone of the leg); 6 - cell of the spinal ganglion; 7 - Gaulle's bundle; 8 - Gaulle's beam core; 9 - bulbotalamic tract ().