During which phase can a neuronal membrane not be stimulated to undergo an action potential?

The refractory period is the phase following an action potential during which a neuron is unable to be stimulated to fire another action potential. This period is crucial for the proper functioning of neurons, as it ensures that action potentials only propagate in one direction along the axon and allows for the resetting of ion concentrations across the neuronal membrane.

During the refractory period, which consists of two distinct phases—the absolute refractory period and the relative refractory period—the neuronal membrane is temporarily unresponsive to additional stimuli. In the absolute refractory period, no new action potential can be generated regardless of the strength of the stimulus. This occurs because the sodium channels remain inactivated after having opened during the action potential. The relative refractory period follows, during which a stronger-than-usual stimulus may induce an action potential, but the likelihood is considerably diminished due to ongoing repolarization and hyperpolarization processes.

In contrast, during depolarization, the membrane is actively becoming more positive and is in the phase of firing an action potential. During resting potential, the neuron is at its baseline state and can be readily stimulated. During hyperpolarization, while the neuron is less likely to fire due to its negative membrane potential, it is still possible for a sufficiently strong stimulus to induce an action potential if it