AEMCA Practice Exam

Which action is associated with muscarinic M3 receptors in the parasympathetic system?

1. Bronchoconstriction and bladder contraction

2. Decreased heart rate and pupil dilation

3. Increased lipolysis and gastric motility

4. Inhibition of gastrointestinal secretions

The correct answer is: Bronchoconstriction and bladder contraction

The action associated with muscarinic M3 receptors in the parasympathetic system includes bronchoconstriction and bladder contraction. Muscarinic M3 receptors are primarily found in smooth muscle and glandular tissues, where their activation leads to various physiological responses. When M3 receptors are stimulated, they promote the contraction of smooth muscles in the bronchi, resulting in bronchoconstriction, which is essential for regulating airflow in the lungs. Additionally, these receptors play a critical role in bladder function by facilitating bladder contraction, contributing to urination. The other options involve actions either unrelated to M3 receptors or representing effects linked to different receptor subtypes or physiological processes. For instance, decreased heart rate and pupil dilation are more accurately associated with M2 receptors. Increased lipolysis and gastric motility do not align with the primary roles of M3 receptors, as lipolysis is typically associated with adrenergic actions. Lastly, the inhibition of gastrointestinal secretions corresponds more with adrenergic activity rather than with the actions mediated by muscarinic receptors.