The term "all-or-nothing phenomenon" has several different meanings in the biomedical sciences:
- 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.
- In cardiology, it refers to the same phenomenon observed in the heart muscle, which will either contract fully or not at all.
- 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 http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.