True or False: Vagal nerve stimulation causes inhibition of the SA and/or AV node, leading to a slower heart rate and decreased contraction.

Vagal nerve stimulation indeed leads to the inhibition of the sinoatrial (SA) and atrioventricular (AV) nodes. The vagus nerve is a crucial component of the parasympathetic nervous system, which functions to regulate heart rate and maintain homeostasis. When vagal tone increases, such as during rest or relaxation, it enhances parasympathetic activity. This results in a decrease in heart rate due to its inhibitory effects on the SA node, which is responsible for initiating the heartbeat, and on the AV node, which controls the conduction of impulses between the atria and ventricles. Additionally, increased vagal stimulation can decrease the force of contraction in the heart, leading to a reduction in cardiac output. This physiological response is essential in managing the body’s energy use and maintaining cardiovascular stability during periods of low demand.