«EVERYTHING OR NOTHING» law

From Big Medical Encyclopedia

«EVERYTHING OR NOTHING» law — empirically established ratio between force of the operating irritant and size of response of excitable structure. According to this law excitable fabric gives the maximum response («everything») with any power of superthreshold irritation (including and threshold) or does not give any answer («anything») at subthreshold irritation (see. Excitability ).

For the first time the similar relations between power of irritation and effect were observed by Boudich (H. Bowditch, 1871). Gradually increasing power of single irritations, it revealed that with the subthreshold power of irritation the muscle of heart is not reduced, and with the threshold power of irritation reduction of heart has the maximum amplitude. At further increase in power of irritation amplitude of reduction does not increase.

Proceeding from the assumption of the chemical nature of process of excitement and its explosive character, Gotch (F. Gotch, 1902) came to a conclusion about applicability of the law «everything or nothing» to nervous tissue. Comparing action currents of a nerve at weak and strong irritations, he found out that duration and a form of currents remain constants. He explained this phenomenon with independence of nervous impulse by nature and forces of the irritant which caused it (if the irritant reached threshold value). Further this consistent pattern was experimentally determined also on single cross-striped muscle fibers.

Physiologists connected manifestation of the law «everything or nothing» in excitable fabrics with the qualitative characteristic of emergence of process of excitement, assuming that «nothing» means total absence of excitement on subthreshold irritation. At achievement of force of the operating irritant of threshold size excitable fabric reacts with full use of all the potentialitys («everything»), as explosion of gunpowder (see. Trigger mechanisms ).

The law «everything or nothing» long time was considered as the general principle of reaction of excitable fabrics. However relativity of this law is experimentally established. It turned out that the muscle of heart not under all conditions answers equally irritants of different force: «everything» changes depending on temperature, an initial muscle strain, degree of her exhaustion.

Researches of excitable structures using thin electrophysiologic methods of a research (see. Electrophysiology ) also relative independence of effect at most of the operating irritant is also established. In single nerve fibril the subthreshold irritation causes the local, not extending change of potential; therefore, it is impossible to say that the irritation does not give «anything». Besides, the all level in turn also changes with change of a functional condition of nerve fibril.

See also Excitement .


Bibliography: I.S's berets. General physiology of a muscular and nervous system, t. 1, M., 1959; Hodorov B. I. Problem of excitability, L., 1969, bibliogr.

Yu. A. Fadeyev.

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