What does the term 'absolute refractory period' refer to?

The term 'absolute refractory period' refers to the phase during which a neuron is unable to generate another action potential, no matter how strong the stimulus is. This occurs primarily because sodium (Na+) channels, which are crucial for the depolarization phase of an action potential, become inactive after they open. During this time, the Na+ channels undergo a conformational change and remain closed, preventing further ion flow and thus inhibiting the initiation of another action potential.

During the absolute refractory period, the state of the Na+ channels is key. The channels that opened in response to a stimulus cannot be reopened until they return to their resting state, even if a significant depolarizing current is applied. Therefore, the correct interpretation of the absolute refractory period emphasizes the closed Na+ channels and their change in conformation, rendering them temporarily inactive.

Other options relate to different aspects of neuronal activity but do not accurately describe the absolute refractory period. The opening of Na+ channels does occur during the action potential but does not characterize the refractory period itself. Membrane potentials like 30mV and resting potentials of -70mV represent different points within the action potential cycle but are not specifically tied to the absolute refractory period.