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all-or-none law

[awl-er-nuhn] /ˈɔl ərˈnʌn/
noun, Physiology
1.
the principle that under given conditions the response of a nerve or muscle fiber to a stimulus at any strength above the threshold is the same: the muscle or nerve responds completely or not at all.
Origin
1895-1900
1895-1900
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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all or none law in Medicine

all-or-none law n.
The principle that the strength by which a nerve or muscle fiber responds to a stimulus is not dependent on the strength of the stimulus. If the stimulus is any strength above threshold, the nerve or muscle fiber will either give a complete response or no response at all.


all'-or-none' adj.
The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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Encyclopedia Article for all or none law

all-or-none law

a physiological principle that relates response to stimulus in excitable tissues. It was first established for the contraction of heart muscle by the American physiologist Henry P. Bowditch in 1871. Describing the relation of response to stimulus, he stated, "An induction shock produces a contraction or fails to do so according to its strength; if it does so at all, it produces the greatest contraction that can be produced by any strength of stimulus in the condition of the muscle at the time." It was believed that this law was peculiar to the heart and that the other highly specialized and rapidly responding tissues-skeletal muscle and nerve-responded in a different way, the intensity of response being graded according to the intensity of the stimulus. It has been established, however, that the individual fibres of both skeletal muscle and nerve respond to stimulation according to the all-or-none principle. This does not mean that the size of response is immutable, because functional capacity varies with the condition of the tissue, and the response to a stimulus applied during recovery from a previous response is subnormal. The size of response, however, is independent of the strength of stimulus, provided this be adequate. The functional response is essentially alike in these specialized tissues-heart, skeletal muscle, and nerve. The response resembles an explosive reaction in that it depletes for a time the available store of energy on which it depends.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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