During an action potential, a second stimulus, no matter how…
During an action potential, a second stimulus, no matter how strong, will not produce a second action potential because the membrane is in its This occurs because the voltage-gated channels are either already open or have proceeded to the state. Immediately after an action potential, some of the voltage-gated channels that repolarized the membrane are still . During this time, a second action potential can be produced, but only if the stimulus strength is This is the , which coincides roughly with the period of . During this time, some of the voltage-gated Na+ channels have returned to their state, and could therefore open again.