Sodium channel activation is triggered by which event?

Sodium channel activation is triggered by which event?

• A. Rapid depolarization to threshold
• B. Hyperpolarization
• C. Maximum diastolic potential
• D. Plateau onset

Answer: (A)

Activation of fast voltage-gated sodium channels occurs when the membrane rapidly depolarizes to threshold. As the cell moves from its resting potential and crosses about -60 to -50 mV, the activation gates open and sodium ions flood in, producing the rapid upstroke of the action potential. Hyperpolarization and the maximum diastolic potential describe the resting state or a return toward rest, not the trigger for opening these channels. The plateau onset happens later, driven mainly by calcium entry, after the initial sodium-driven upstroke has occurred. So the key trigger is rapid depolarization to threshold.

Activation of fast voltage-gated sodium channels occurs when the membrane rapidly depolarizes to threshold. As the cell moves from its resting potential and crosses about -60 to -50 mV, the activation gates open and sodium ions flood in, producing the rapid upstroke of the action potential. Hyperpolarization and the maximum diastolic potential describe the resting state or a return toward rest, not the trigger for opening these channels. The plateau onset happens later, driven mainly by calcium entry, after the initial sodium-driven upstroke has occurred. So the key trigger is rapid depolarization to threshold.