Question

When you determined the relative refractory period, you actually recorded the interval when a few neurons entered the relative refractory period. Explain why at this interval only some neurons have entered the relative refractory period.

Answer 1

Ans: The relative refractory period is the interval of time during which a second action potential can be initiated, but initiation will require a greater stimulus than before. Refractory periods are caused by the inactivation gate of the Na⁺ channel. This is the time during which another stimulus given to the neuron will not lead to a second action potential. Thus, because Na⁺ channels are inactivated during this time, additional depolarizing stimuli do not lead to new action potentials. The absolute refractory period takes about 1-2 ms.

This period during which a stronger than normal stimulus is needed in order to elicit an action potential is referred to as the relative refractory period (RRP). During this process, since p_K remains above its resting continued K⁺ to flow out of the cell would tend to oppose any depolarization caused by the opening of Na⁺ channels that have recovered from inactivation.