[Campbell Biology P.1124] Which of the following statements accurately describes the ionic ev... | Practice Question

Which of the following statements accurately describes the ionic events during the rising and falling phases of an action potential?

  • A: During the rising phase, voltage-gated K+ channels open, leading to K+ outflow.
  • B: The falling phase is characterized by the inactivation of voltage-gated Na+ channels and the opening of voltage-gated K+ channels, causing K+ outflow.
  • C: The undershoot phase occurs when the membrane's permeability to Na+ is higher than at rest, making the potential closer to ENa.
  • D: The rising phase brings the membrane potential toward EK, due to rapid Na+ influx.

Explanation

The rising phase is caused by the rapid influx of Na+ as voltage-gated Na+ channels open, bringing the membrane potential closer to ENa. The falling phase is due to the inactivation of Na+ channels and the opening of voltage-gated K+ channels, which leads to K+ outflow and repolarization back toward EK. The undershoot phase is characterized by an even higher permeability to K+ than at rest, bringing the membrane potential closer to EK before it returns to resting potential.