IRRITATION — the action on living tissue (cell) of external factors (irritants) leading to active change of nature of its life activity. Ability of living tissue to answer R. with change of nature of the life activity is called irritability (see). The most difficult of such answers is excitement (see) — active reaction, the cut is one of tasks information transfer about properties of the irritants operating on a cell (see). Reaction of excitement is characteristic of nervous, muscle and secretory cells. The River
is the cornerstone the specific molecular organization of a superficial cell membrane (see. Membranes biological ). In a superficial membrane there are macromolecules of the proteinaceous nature having receptor properties — ability to react to action of an irritant change of the structure. These structural changes lead to emergence of the specific signal which is transmitted through a superficial membrane in a cell and, in turn, «starting» a chain physical. - chemical and biochemical, the processes creating response of a cell. The most universal type of such signal is generation of transmembrane current of inorganic ions (ions of sodium, potassium, calcium, chlorine) which distribution between cytoplasm of a cell and the extracellular environment unevenly in connection with activity of the transport fermental systems (ionic pumps) localized in a superficial membrane. At rest the superficial membrane badly passes these ions (see Permeability). However the proteinaceous macromolecules which are built in a membrane under the influence of R. gain ionic conduction (through so-called ion channels). Along with ionic type of transmembrane signal transmission also more difficult mechanisms are possible (see. Transport of ions ).
Two types of irritant action on a cellular membrane — chemical and electric are studied most in detail. In the first case the external irritant enters chemical reaction with special receptor groups of membrane macromolecules; this reaction then causes the restructurings which are followed by changes of an ionic conduction of a membrane. The chemical structure of receptor groups widely varies, as defines specific sensitivity of various cells to these or those chemical irritants. In chemical R.'s organism it is used not only for interaction with the environment, but also for signaling from a cell to a cell (see. Synapse ). In the second case the macromolecules which are built in a superficial membrane have ability to react to change of external electric field thanks to existence in their structure of the loaded groups displaced electrically; shift of these groups leads to change of an ionic conduction of a membrane. Though external electric R. in nature occurs extremely seldom (electroreception at some fishes), such R. plays a paramount role in activity of excitable fabrics, being a basis of self-spread of activation on a cell. Therefore for excitement of fabrics electric current is the most universal artificial irritant especially convenient in connection with ease of its precision measurement and dosing. In the practical purposes for R. of fabrics use generally electronic stimulators (see. Electrostimulation ).
The nature of irritant action of irritants of other types (mechanical, temperature, light) is not clear yet. It is possible that formation of the active chemical agents interacting then with the relevant chemical receptor groups of membrane receptors is its cornerstone.
Bibliography: Ginetsinskiya. G. Chemical transfer of nervous impulse and evolution of muscular function, L., 1970; Katts B. A nerve, a muscle and a synapse, the lane with English, M., 1968; General physiology of a nervous system, under the editorship of P. G. Kostya and A. I. Roytbak, page 85, L., 1979; Hodzhkin A. Nervous impulse, the lane with English, M., 1965.
P. G. Kostiuk.