Gag Reflex Afferent — FRCA Primary MCQ

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ModerateAnatomyGag Reflex AfferentFRCA Primary

During cranial nerve examination, stimulation of the left posterior pharyngeal wall produces no gag response. Stimulation of the right posterior pharyngeal wall produces a bilateral response, and palatal elevation during phonation is symmetrical. Which cranial nerve carries the afferent limb from the left posterior pharyngeal wall?

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Correct answer: C — Glossopharyngeal nerve (CN IX)

The correct answer is C, the glossopharyngeal nerve (CN IX). Sensory stimulation of the posterior pharyngeal wall is conveyed predominantly through CN IX to the medulla, forming the afferent limb of the gag reflex. The vagus nerve (CN X) provides the efferent limb through motor supply to the palatal and pharyngeal muscles. Here, a bilateral response after right-sided stimulation and symmetrical palatal elevation indicate that the vagal motor pathway is intact; failure after left-sided stimulation therefore localises to the left afferent pathway. CN V supplies much of the facial and anterior oral somatic sensation, CN VII carries taste from the anterior two-thirds of the tongue, and CN XII is the motor nerve to the tongue.

Reference: BMJ Best Practice, Assessment of cranial nerve mononeuropathy, Glossopharyngeal and vagus nerve-testing sections, current online version accessed 19 August 2026. https://uhmeded.uhcw.nhs.uk/Portals/0/AssetUploads/CHESS%20Book%20Clinical%20Skills%20Workbook%202022-23.pdf?ver=ELcRsPPRSWHk3baBgJ2INQ%3D%3D