During carotid endarterectomy, the surgeon stimulates the carotid sinus and causes bradycardia and hypotension. The afferent limb of this reflex is carried by which nerve to the brainstem?

• A Vagus nerve (CN X)
• B Cervical sympathetic fibres via the carotid plexus
• C Internal laryngeal nerve (branch of superior laryngeal nerve)
• D Glossopharyngeal nerve (CN IX) via Hering's nerve ✓

Explanation

The carotid sinus baroreceptor reflex is mediated by the sinus nerve of Hering, a branch of the glossopharyngeal nerve (CN IX). Mechanical or chemical stimulation of the carotid sinus activates these stretch receptors; impulses travel via CN IX to the nucleus tractus solitarius in the medulla, triggering the cardioinhibitory (vagal) efferent response that produces bradycardia and hypotension. Local anaesthetic block of CN IX prior to carotid surgery prevents this haemodynamic response.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.