Which of the following does not occur when norepinephrine is released onto pacemaker cells? A) The permeability of Na⁺ channels increases. B) The resting potential drifts up more rapidly. C) The permeability of Ca²⁺ channels increases. D) The interval between action potentials increases. E) The heart beats faster.

Question

Quizplus · Accepted Answer

Norepinephrine is a neurotransmitter that generally increases heart rate by increasing the rate of depolarization of pacemaker cells. This is achieved by increasing the permeability of the If channels to Na+ and the permeability of the Ca2+ channels. As a result, the resting potential drifts up more rapidly (B) and the heart beats faster (E). Furthermore, the interval between action potentials decreases (not increases), leading to a faster heart rate. Therefore, the correct answer is D, which is the opposite of what would happen with norepinephrine release.

Which of the Following Does Not Occur When Norepinephrine Is