AEMCA Practice Exam

What function is associated with muscarinic M2 receptors in the parasympathetic system?

1. Activate bronchoconstriction

2. Reduce heart rate by acting on the heart

3. Control salivation and digestion

4. Enhance gastric acid secretion

The correct answer is: Reduce heart rate by acting on the heart

The function associated with muscarinic M2 receptors in the parasympathetic system is the reduction of heart rate through their action on cardiac tissues. Muscarinic M2 receptors, when activated by acetylcholine, primarily influence the heart by decreasing the heart rate. This effect is facilitated by the receptors' location on the atrial muscle and the sinoatrial node, leading to a decrease in conduction velocity and an overall reduction in cardiac output, which is characteristic of the parasympathetic nervous system’s role in promoting a restful state. While bronchoconstriction and control of salivation and digestion are indeed functions of the parasympathetic system, those actions are typically mediated by different receptors or pathways. For instance, bronchoconstriction is more closely related to the effects of other muscarinic receptor types, while gastric acid secretion is mainly influenced by other factors, such as gastrin and histamine, rather than being directly connected to M2 receptor activation. Thus, the specificity of M2 receptors for reducing heart rate in the parasympathetic context is what distinguishes this function.