The term "all-or-nothing phenomenon" has several different meanings in the biomedical sciences:

  1. It refers to a phenomenon where the strength of a nerve impulse is not dependent on the strength of the stimulus. Instead, there is a threshold level of stimulus strength that must be reached before the nerve will fire an impulse (at full capacity). Below the threshold, the nerve will not fire at all.

  2. In cardiology, it refers to the same phenomenon observed in the heart muscle, which will either contract fully or not at all.

  3. In studies of behavior, it refers to the same phenomenon where a behavioral stimulus will either produce a complete response or no response at all.

This is also called the all-or-nothing principle, all-or-none law, all-or-none responsiveness, etc. For related information, see Kolmogorov's 0-1 law and phase transition.

From the BioTech Dictionary at For further information see the BioTech homenode.

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