THERMORECEPTORS (Greek therme warmth, heat + lat. to accept recipere) — the nervous educations specifically sensitive to changes of temperature of the environment surrounding them. Transferring information on changes of ambient temperature, T. play an important role in thermal controls (see) an organism. T. at the person hl are located. obr. in integuments of a body, mucous membranes of a mouth, upper respiratory tracts, a stomach and a rectum, walls of saphenas, bilious and a bladder, a uterus and external genitals, a hypothalamus, an average and spinal cord. The greatest density of T. in face skin, it is less of them on a trunk, it is even less on the lower extremities.
Skin of the person possesses pointed distribution of sensitivity to heat and cold. Heating of one points of skin causes a caumesthesia (a point of «heat»), cooling of others — a cryesthesia (a point of «cold»). Quantity of points of «heat» approximately 10 times less than points of «cold». It is possible that the relative lack of points of «heat» on the periphery is compensated by existence in a hypothalamus of thermal receptors, to-rye react to temperature increase of blood and participate in start of mechanisms of a thermolysis. The quantity of cold and thermal points on a certain site of skin constantly changes depending on the initial level of its temperature, intensity of irritation, and also a temperature schedule of other sites of a body surface.
At any ambient temperature, compatible to life, from peripheral T. on nerve fibrils in c. the item of page arrives a stationary impulsation. Stationary categories of thermal receptors are observed with the temperature range from 20 to 50 °, stationary categories of cold receptors — in the range from 10 to 41 °. At a temperature below 10 ° cold receptors and nerve fibrils of gomoyotermny animals are blocked. At a temperature over 45 ° cold receptors can be activated again. This secondary manifestation of activity of cold receptors explains the phenomenon of a paradoxical cryesthesia observed at strong heating. Strengthening of activity of cold and thermal T. takes place up to t ° 50 °, at more high temperatures of T. are damaged. At t ° 47 — 48 ° along with T. also pain receptors begin to be excited. Explain these unusual sharpness of a paradoxical cryesthesia.
On rapid cooling specific cold T. react sharp increase in frequency of the generated categories; they do not react to bystry warming absolutely or reduce the frequency of an impulsation. Thermal T. increase the frequency of an impulsation in response to bystry warming; rapid cooling is followed by reduction of frequency of pulse categories of thermal T. Period of increase of frequency of an impulsation of T. at change of ambient temperature soon is replaced by the period of its gradual reduction despite the continuing action of an irritant then the frequency of pulse categories T. is established at the new stationary level that is followed by disappearance of a caumesthesia or cold.
Excitement of T. depends as on absolute values of temperature of skin in the place of irritation, and on speed and extent of its change. One T. others react to temperature drop in 0,1 ° — on difference in 1 °, the third are excited when temperature drop reaches 10 °. Idiosyncrasy of T. existence of an optimum of sensitivity at them to irritation is, as criterion to-rogo serves generation by thermoreceptors of an impulsation of the maximum frequency. For cold receptors the optimum of sensitivity lies within t ° 25 — 30 °, for thermal — within 38 — 43 °. In these areas the minimum change of temperature causes the greatest reaction of T.
Along with specific T. in skin there is a big group of receptors, to-rye react both on thermal, and to mechanical irritation. As a rule, such nonspecific T. are excited by fall of temperature of skin owing to what them call tactile and cold. Information on changes of temperature of skin is transferred by these receptors with longer stage of latency and with a smaller frequency of impulses unlike specific T. Besides, more high speed of adaptation to cold irritation is inherent to tactile and cold receptors.
Innervation of T. it is carried out by preferential fine myelin fibers of the A-delta group and amyelenic fibers of group C.
At the person apply a method of the quantitative accounting of thermosensitive points on a certain area of skin to a research of thermoreception. In an experiment apply electrophysiologic methods of a research of pulse activity in the sensitive fibers connected with T.
Bibliography: Ivanov K. P. The temperature alarm system and its processing in an organism, in book: Mechanisms of processing of information in touch systems, under the editorship of V. D. Glezer, etc., page 7, L., 1975; Minut-Sorokhtina O. P. Fiziologiya of thermoreception, L., 1972, bibliogr.; Skin of vertebrates, ed. by R. I. C. Spearman a. P. A. Riley, p. 255, L., 1980.
A. I. Esakov.