REFRAKTERNOST

From Big Medical Encyclopedia

REFRAKTERNOST (Latin refractorius unreceptive) — the condition of excitable educations after the previous excitement which is characterized by decrease or lack of excitability. For the first time R. was found in a muscle of heart by E. Marey in 1878, and in nerves — Gotchem and Burke (F. Gotch, Page J. Burck) in 1899.

Changes excitabilities (see) nervous and muscle cells are connected with changes of level of polarization of their membranes at emergence of process excitement (see). At reduction of size of membrane potential excitability slightly increases and if after reduction of membrane potential there is an action potential, then excitability completely disappears and the cell membrane becomes insensitive (refractory) to any influences. This fortune of full not excitability was come into by the name of a phase of the absolute River. For the fast-carrying-out nerve fibrils of hematothermal animals its duration makes 0,4 ms, for skeletal muscles of 2,5 — 4 ms, for muscles of heart — 250 — 300 ms. Recovery of initial level of membrane potential is followed by increase in level of excitability and the membrane gains ability to react to superthreshold irritants (relative R.'s phase). In nerve fibrils relative R. lasts 4 — 8 ms, in a muscle of heart — 0,03 ms. Relative R.'s phase is replaced by a phase of a hyperexcitability (an ekzaltatsionny phase P.), edges is characterized by increase in excitability against initial level and is connected with trace depolarization (negative afterpotential). The subsequent after hyperpolarization (positive afterpotential) is followed by secondary decrease in excitability, edge then is replaced by normal excitability at recovery of size of rest potential of a membrane.

All phases P. are connected with origins and changes of membrane potentials and caused by kinetics of permeability of membranes for ions (see. Bioelectric potential ). Duration of phases P. can be determined, applying a method of pair irritations at different intervals between them. The first irritation is called conditioning — it causes process of excitement in excitable fabric; the second — testing — shows the level of excitability of fabric and a phase P.

Age changes, influence of nek-ry medicinal substances, thermal and other factors can exert impact on excitability and, therefore, on duration and expressiveness of separate phases P. Use it for the purpose of management of excitability of fabric at treatment of nek-ry diseases. E.g., lengthening of a phase of relative R. in a muscle of heart leads to decrease in frequency of its reductions and elimination of arrhythmia. R.'s changes caused by disturbance of ionic origins of excitement are observed at a number of diseases of a nervous system and muscles.



Bibliography: Beritashvili I. S. General physiology of a muscular and nervous system, t. 1, M., 1959; B of p e e M. A. Electric activity of a nervous system, the lane with English, M., 1979; To Oka Page. Fundamentals of neurophysiology, the lane with English, M., 1969; Hodorov B. I. General physiology of excitable membranes, M., 1975, bibliogr.; Gotch F. and. In u of with k of Page J. The electrical response of nerve to two stimuli, J. Physiol. (Lond.), v. 24, p. 410, 1899.


Yu. A. Fadeyev.

Яндекс.Метрика