In the carotid triangle, the carotid body and carotid sinus lie at the bifurcation of the common carotid artery. Which nerve carries afferent impulses from the carotid body chemoreceptors to the brainstem?

• A Sympathetic fibres from the superior cervical ganglion
• B Internal laryngeal nerve (branch of CN X)
• C Hypoglossal nerve (CN XII)
• D Sinus nerve of Hering (branch of CN IX) ✓

Explanation

The carotid body (chemoreceptor detecting PaO2, PaCO2, and pH) and carotid sinus (baroreceptor on the internal carotid artery wall) send afferent signals via the sinus nerve of Hering — a branch of the glossopharyngeal nerve (CN IX) — to the nucleus tractus solitarius (NTS) in the medulla. The NTS integrates cardiovascular and respiratory reflexes. Some vagal (CN X) fibres also contribute a small afferent supply. The superior cervical ganglion provides sympathetic efferents to the carotid body, modulating its sensitivity, but does not carry the primary afferent signal to the CNS.

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

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Written and medically reviewed by the StethoPrep medical team.