The peak potential during an action potential is closest to which value?

The peak potential during an action potential is closest to which value?

• A. -70 mv
• B. +40 mv
• C. +70 mv
• D. 0 mv

Answer: (B)

During an action potential, the neuron depolarizes from a typical resting potential of about -70 mV as voltage-gated Na+ channels open and Na+ rushes into the cell. The depolarization continues until these Na+ channels begin to inactivate and voltage-gated K+ channels open, allowing K+ to leave. This opposing K+ current and the inactivation of Na+ channels prevent the membrane from reaching the Na+ equilibrium potential, so the peak of the action potential is limited to around +40 mV. In contrast, the Na+ equilibrium potential itself is closer to +60 to +70 mV, but the peak is lower due to the changing channel states and the outward K+ current. Resting potential sits around -70 mV, and 0 mV is not the peak. Therefore, +40 mV is the best characterization of the peak.

During an action potential, the neuron depolarizes from a typical resting potential of about -70 mV as voltage-gated Na+ channels open and Na+ rushes into the cell. The depolarization continues until these Na+ channels begin to inactivate and voltage-gated K+ channels open, allowing K+ to leave. This opposing K+ current and the inactivation of Na+ channels prevent the membrane from reaching the Na+ equilibrium potential, so the peak of the action potential is limited to around +40 mV. In contrast, the Na+ equilibrium potential itself is closer to +60 to +70 mV, but the peak is lower due to the changing channel states and the outward K+ current. Resting potential sits around -70 mV, and 0 mV is not the peak. Therefore, +40 mV is the best characterization of the peak.