A medical student performs carotid sinus massage on a volunteer. Heart rate falls promptly from 72 to 50 beats per minute. The afferent limb of this reflex travels in which nerve, and the efferent limb in which nerve?

• A Afferent: vagus; efferent: glossopharyngeal
• B Afferent: glossopharyngeal; efferent: sympathetic chain
• C Afferent: vagus; efferent: vagus
• D Afferent: glossopharyngeal; efferent: vagus ✓

Explanation

Baroreceptors in the carotid sinus send their impulses through the sinus (Hering) nerve, a branch of the glossopharyngeal nerve, to the nucleus tractus solitarius. The efferent response is increased vagal (parasympathetic) traffic to the sinoatrial node, producing bradycardia. Option B is tempting because the sympathetic limb is suppressed during this reflex, but suppression is not conduction; the active efferent change is vagal.

Reference: Guyton and Hall Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.