During the relative refractory period, which statement is true?

During the relative refractory period, which statement is true?

• A. A stronger stimulus can evoke an action potential.
• B. A stronger stimulus can elicit an AP as the membrane is partially repolarized.
• C. The neuron is hyperpolarized.
• D. Na+ channels are fully inactivated.

Answer: (B)

During the relative refractory period, excitability returns gradually as some voltage‑gated Na+ channels recover from inactivation while K+ conductance is still helping drive repolarization. This creates a window where the membrane is moving back toward resting potential but still has a higher threshold. Because enough Na+ channels have recovered, a stronger-than-normal stimulus can push the membrane to threshold again and trigger another action potential. The phrase “as the membrane is partially repolarized” captures both the state of channel recovery and the higher threshold, which is why this option is the best description. The other statements don’t fit as precisely: a stronger stimulus alone is not always sufficient without noting the partially repolarized state; the neuron isn’t simply hyperpolarized throughout the phase; and Na+ channels are not all still inactivated during this period.

During the relative refractory period, excitability returns gradually as some voltage‑gated Na+ channels recover from inactivation while K+ conductance is still helping drive repolarization. This creates a window where the membrane is moving back toward resting potential but still has a higher threshold. Because enough Na+ channels have recovered, a stronger-than-normal stimulus can push the membrane to threshold again and trigger another action potential. The phrase “as the membrane is partially repolarized” captures both the state of channel recovery and the higher threshold, which is why this option is the best description. The other statements don’t fit as precisely: a stronger stimulus alone is not always sufficient without noting the partially repolarized state; the neuron isn’t simply hyperpolarized throughout the phase; and Na+ channels are not all still inactivated during this period.