During the absolute refractory period, what happens to the Na+ channels?

During the absolute refractory period, what happens to the Na+ channels?

• A. They are opened.
• B. They are inactivated.
• C. They are activated.
• D. They are degraded.

Answer: (B)

During the absolute refractory period, voltage-gated Na+ channels are inactivated. After they open to drive the rapid depolarization of the action potential, an inactivation mechanism closes the channels even though the membrane is still depolarized. This inactivated state blocks Na+ entry and cannot be overcome by a new stimulus, so another action potential cannot be produced until the channels recover from inactivation. Recovery requires repolarization and resetting of the gates back to the closed state, at which point the channels can be activated again. This guarantees unidirectional propagation and sets the minimum interval between successive action potentials.

During the absolute refractory period, voltage-gated Na+ channels are inactivated. After they open to drive the rapid depolarization of the action potential, an inactivation mechanism closes the channels even though the membrane is still depolarized. This inactivated state blocks Na+ entry and cannot be overcome by a new stimulus, so another action potential cannot be produced until the channels recover from inactivation. Recovery requires repolarization and resetting of the gates back to the closed state, at which point the channels can be activated again. This guarantees unidirectional propagation and sets the minimum interval between successive action potentials.