all-or-none law

n. 1. In neurophysiology, the theory that the axon of any neuron propagates its impulse at full strength or does not propagate an impulse at all. Thus the strength of a neural input does not affect the strength of the next neuron's output though it may affect the frequency of impulses. 2. In learning, the theory that associations are formed in a single trial. If an association is formed in a single trial, its strength may be increased by further trials but the association itself is an all-or-none situation.