From Big Medical Encyclopedia

IRRITANTS — the external impacts on a cell of a live organism causing active (i.e. connected with internal energy sources) change of nature of its life activity. The most widespread R. are mechanical, chemical, electric, temperature and light influences. Many R. directly interact with the perceiving structures of a cell, some can have the effect on a cell only indirectly. So, force of terrestrial gravitation — gravitation — is perceived through intermediate mechanical Rubles. Irritants, to the Crimea the corresponding cells are especially adapted, call adequate. At R.'s interaction to the structures perceiving it in them there are certain reorganizations «starting» this or that sequence physical. - chemical and biochemical reactions of a cell (see. Irritation ). Thus, R. in essence are the signals causing quick response of an organism to changes in the environment of its dwelling.

Living tissue (cell) can have receptor structures for several types P.; at the same time existence of the cells which are specially adapted for perception of certain types P. is characteristic of more difficult organisms (see. Receptors ). Such specialization of cells is expressed in extraordinary increase in their sensitivity at the expense of special mechanisms of transformation of energy of an irritant in energy, the most suitable for start of the subsequent cellular processes.

R.'s parametrization is made by measurement of force of the corresponding external influence; the last is expressed in sizes of its energy referred at a size of the perceiving surface. In physiology assessment of force of influence of R. on caused by them fiziol, to effect was widely adopted; at the same time it is considered that dependence between R.'s force and response of a cell always has nonlinear character (through participation in operation of R. on a cell of composite reaction of the relevant receptor structure). Reaction develops only at R.'s achievement of a certain threshold value; reactions do not cause subthreshold R. Superthreshold R. can be compared among themselves on that, in how many time their force exceeds threshold value. Strengthening of reaction at R.'s strengthening happens only to a certain limit; The Rubles causing limit reaction are called maximum.

System reaction of an organism to R. is based on set of reactions of the sensory cells starting the related reflex activity of a nervous system (see). At the same time certain R. can remain for an organism indifferent (indifferent) though they also are perceived by the corresponding sensory cells; response can be absent because the signal going from sensitive structures is insufficient for activation of the subsequent nervous structures or its passing is blocked by processes of the central braking (see). Rubles who cause system response are allocated on the nature of the reaction and designated as food, defensive, sexual, approximate, locomotory, etc. At various patol, processes proceeding in an organism, strong R. can arise in its fabrics due to change of normal structure of internal environment and other disturbances.

According to I. P. Pavlov's doctrine about uslovnoreflektorny activity unconditional and conditional Rubles distinguish. Conditional R. name external influence, a cut as a result of numerous coincidence to action of the irritants which are constantly causing response of an organism (unconditional R.) gain ability to cause the reactions characteristic for unconditional (see. Conditioned reflex ). In case of not reinforcement conditional R. lose alarm value and become indifferent. Conditional R. subdivide on natural and artificial; they can have both the exciting, and braking value in activity of an organism. The person in connection with development of the second alarm system by conditional R. has a word (see. Speech ).

Bibliography: Granite P. An electrophysiologic research of reception, the lane with English, M., 1957; To about with t yu to P. G. Fiziologiya of the central nervous system, page 178, etc., Kiev, 1977; General physiology of a nervous system, under the editorship of P. G. Kostiuk and and A. I. Roytbaka, L., 1979; Pavlov I. G1. Complete works, t. 3, book 1 — 2, M. — L., 1951.

P. G. Kostiuk.