What phenomenon occurs when voltage gated Na channels haven't fully reset yet?

When voltage-gated sodium channels haven't fully reset, the membrane is in a state where it is less capable of responding to additional stimuli. During an action potential, these channels open rapidly in response to depolarization, allowing sodium ions to flow in, which contributes to the rising phase of the action potential. After the action potential, these channels enter an inactivated state, during which they cannot be reopened immediately until they reset back to their closed state.

In this scenario, a larger stimulus is indeed required to reach the threshold for depolarization because the inactivation phase temporarily prevents the channels from opening in response to normal stimuli. This phenomenon elevates the threshold for generating a new action potential, meaning that the usual level of depolarization that would trigger an action potential is no longer sufficient. Therefore, any subsequent stimulation must be stronger to elicit an action potential, reflecting the need for a larger stimulus to compensate for the reduced availability of functional sodium channels. This understanding is essential in grasping the relationship between channel dynamics and neuronal excitability.