CVS Practice Test

During the resting state of phase 4 in a non-pacemaker action potential, potassium channels play a crucial role in maintaining the membrane potential. In this state, some potassium channels are indeed closed to help stabilize the resting membrane potential, while others may be leaky. These leaky channels allow a small, steady flow of potassium ions out of the cell, which is essential for maintaining the negative resting potential inside the cell compared to the outside.

The presence of both closed and leaky potassium channels ensures that the cell is ready to respond to the next depolarization event, as the channels can quickly open in response to stimuli. This balance is critical for the excitability of the cell and its ability to propagate action potentials effectively.

The other options do not accurately reflect the state of potassium channels during phase 4; if all channels were open, the cell would be unable to maintain a resting potential, and if they were inactive or blocked, the cell would not effectively prepare for the next action potential.