[Campbell Biology P.1123] Which of the following statements correctly describes the events oc... | Practice Question

Which of the following statements correctly describes the events occurring during phase 4 Falling phase of the action potential as shown in Figure 48.12?

  • A: Most voltage-gated sodium channels are open, leading to Na+ influx.
  • B: Most voltage-gated potassium channels open, causing K+ outflow, while sodium channels become inactivated.
  • C: Both gated sodium and potassium channels are closed, maintaining resting potential.
  • D: Some sodium channels open, and Na+ inflow depolarizes the membrane to threshold.

Explanation

According to the text for phase 4, 'Most sodium channels become inactivated, blocking Na+ inflow. Most potassium channels open, permitting K+ outflow, which makes the inside of the cell negative again.' This accurately matches option B.