What happens to the heart rate during a parasympathetic response?

The heart rate decreases during a parasympathetic response due to the activation of the parasympathetic nervous system, primarily through the action of the vagus nerve. The parasympathetic nervous system is responsible for the "rest and digest" functions of the body, promoting a state of relaxation and conserving energy. When stimulated, it releases acetylcholine, which acts on the heart to slow down the firing rate of the sinoatrial (SA) node, the natural pacemaker of the heart. This results in a lower heart rate, which is essential for allowing the body to restore itself and maintain homeostasis after periods of stress or activity.

In contrast, the sympathetic nervous system, which is activated during times of stress or danger, accelerates the heart rate to prepare for 'fight or flight' responses. The correct answer highlights the specific effect of parasympathetic activity on heart function, showcasing the balance between the two branches of the autonomic nervous system in regulating physiological responses.