From Big Medical Encyclopedia

EXCITABILITY — ability of high-organized fabrics (nervous, muscular, ferruterous) to react to irritations change of physiological properties and generation of process of excitement. The fabrics having this ability are called excitable. Is one of forms century irritability (see) also provides the most optimum adaptation of organisms to the changing conditions of the environment.

In the course of evolution of a cell of some fabrics (first of all nervous) adapted quickly to react to irritation. However intensity, duration and speed of reactions in response to irritations are not identical to various living tissues. The minimum (critical) size of influence causing the extending process of excitement is called an excitation threshold.

All environmental factors can under the known conditions be the irritants causing reaction of living tissue. However certain fabrics possess specific V., i.e. hypersensitivity to adequate irritants, napr, visual receptors — to light, acoustical — to a sound etc. In experimental physiology development of a problem B. at observations over a complete organism is carried out by use of adequate irritants, i.e. the corresponding subjects, to - ry affect an organism under natural conditions. In experiences on the isolated fabrics and bodies electric current is usually used, to-ry it is closest to external manifestation of process of V. and it can be precisely graduated on force, duration and the nature of the influence.

It is inseparably linked with features of functions of a superficial cell membrane century (see. Membranes biological ). The membranes capable to generation of pulse action potentials at irritation, refer to categories of electroexcitable membranes, and the membranes not capable to pulse electrogenesis — to electrounexcitable membranes. Electroexcitability call ability of a membrane to generation of action potentials. Sravnitelnofiziologichesky features of a cell — its V. are the reason of distinctions in ability to electrogenesis of membranes and lability (see).

For definition fiziol, properties of separate links of functional systems of a complete organism there is a concept «selective excitability», i.e. V. in relation to certain factors of surrounding and internal environment, napr, to hormones, mediators, an osmotic factor, etc. It is especially possible to raise a question of so-called trigger excitability, i.e. ability of fabric to react to irritation with use trigger mechanism (see), starting function of this fabric or body.

See also Excitement .

Bibliography: Vvedensky H. E. Complete works, t. 4, L., 1953; Latmanizova L. V. Sketch of physiology of excitement, M., 1972; Ukhtomsky A. A. Collected works, t. 4, L., 1945; Hodgkin A. L. The conduction of the nervous impulse, Liverpool, 1965; Katz B. Electric excitation of nerve, Oxford, 1939.

L. V. Latmanizova.