Question

Which of the following is an effect of parasympathetic activity to the heart?

A) Postganglionic neurons release acetylcholine, which binds to nicotinic cholinergic
receptors in the SA node.
B) SA nodal cells are depolarized.
C) Heart rate is increased.
D) The rate of spontaneous depolarization in SA nodal cells decreases.
E) cAMP is activated.

Answer 1

Parasympathetic activity to the heart slows down heart rate by decreasing the rate of spontaneous depolarization in SA nodal cells.

Step-by-step explanation:

Parasympathetic activity to the heart affects heart rate by slowing it down.

This is accomplished through the release of acetylcholine (ACh) which binds to muscarinic receptors in the SA node. This causes SA nodal cells to hyperpolarize, making it more difficult for them to reach the threshold for generating an action potential. As a result, the rate of spontaneous depolarization in SA nodal cells decreases, leading to a decrease in heart rate.

In contrast, sympathetic activity increases heart rate by releasing norepinephrine (NE) onto adrenergic receptors in the SA node, which causes the cells to depolarize faster.