Dictionary of Biological Psychology
A property of an ACTION POTENTIAL describing the fact that once THRESHOLD has been reached the amplitude is not dependent on the size of the stimulus, but on the properties of the underlying ION CHANNEL.
If threshold is reached, the action potential proceeds to its full amplitude (all), but if threshold is not reached, the action potential does not occur (none) and the change in membrane potential dissipates. This principle does not mean that all action potentials are the same size, even in the same neuron, as changes in the ionic environment may cause changes in the absolute size or shape of the action potential.
DOUGLAS D.RASMUSSON
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