all or none law

Main Entry: all–or–none law
Function: noun
: a principle in physiology: in any single nerve or muscle fiber the response to a stimulus above threshold levelis maximal and independent of the intensity of the stimulus

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.

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all'-or-none' adj.