What is the effect of parasympathetic stimulation on heart rate?

Parasympathetic stimulation primarily has a decreasing effect on heart rate. This is achieved through the action of the vagus nerve, which releases acetylcholine at the heart's pacemaker cells, primarily located in the sinoatrial (SA) node. The release of acetylcholine slows down the rate of depolarization in the pacemaker cells, effectively reducing the heart rate.

In a typical resting state, the parasympathetic nervous system is dominant, and stimulation leads to a decrease in heart rate, promoting a state of rest and recovery in the body. This is in contrast to sympathetic stimulation, which increases heart rate by enhancing cardiac output during times of stress or exertion. Understanding the balance between these two branches of the autonomic nervous system is crucial when studying cardiac physiology and dysrhythmias.