All-or-None Phenomena

Definition

The principle stating that once an action potential is initiated, it will always fire at full strength. There is no partial or graded response; either it occurs completely or not at all.

Related terms

Subthreshold Stimulus: A stimulus that is not strong enough to generate an action potential in a neuron.

Overshoot: The phase during an action potential where the voltage inside the neuron becomes more positive than resting membrane potential.

Refractory Period:

A brief period after an action potential when another stimulus cannot initiate another action potential.