Neurons, Nervous System, And Signal Transmission Practice Test

The question tests how a neuron’s ability to fire again changes right after an action potential. After firing, there are two refractory phases that change excitability. During the absolute refractory period, the voltage-gated Na+ channels are inactivated and cannot reopen, so no stimulus—regardless of strength—can elicit another action potential. As those channels recover and the membrane returns toward resting potential, the absolute period ends and a relative refractory period begins. In this phase, some channels are ready to open again, but the membrane is hyperpolarized, so a higher-than-normal stimulus is needed to reach threshold and trigger another action potential. So the correct description is that the absolute refractory period has no possible action potential, while the relative refractory period requires a stronger-than-normal stimulus to evoke one.