All-or-None Law(redirected from all-or-none phenomenon)
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all-or-none law[¦ȯl ər ¦nən ‚lȯ]
in physiology, the fact that excitable tissue (nervous and muscular) apparently will not respond at all to a stimulus if it is inadequate (subthreshold) or will respond maximally if the stimulus is of threshold magnitude. A further increase in the force of the stimulus will not alter the magnitude or duration of the tissue response. The all-or-none law was derived from a broad interpretation of the data obtained by H. Bowditch (USA, 1871) in stimulating the cardiac ventricle of a frog. Further research demonstrated the relativity of the law (more precisely, principle): a stimulus close to threshold force provokes a local response in the area stimulated; a stimulus of more than threshold force provokes a response, recorded from its action potential, that may in-crease, depending on the condition of the tissue stimulated.