DAY 2 — CASE 6 (Hairy tongue): The lesion is in the POSTERIOR 1/3 of the tongue. If a biopsy were performed in this area, which nerve could be damaged?

Correct answer: B. Glossopharyngeal nerve (CN IX)

• A. The vagus nerve (CN X) provides some pharyngeal sensation and motor supply to the pharynx but is not the primary sensory nerve of the posterior tongue mucosa.
• B. The GLOSSOPHARYNGEAL NERVE (CN IX) provides BOTH general sensation AND taste sensation to the POSTERIOR 1/3 of the tongue. A biopsy of the posterior tongue risks damaging CN IX, which would affect taste (posterior tongue) and potentially trigger or damage the gag reflex (CN IX mediates the sensory limb).
• C. CN V3 (lingual nerve, branch of trigeminal) provides general sensation to the ANTERIOR 2/3 of the tongue — not the posterior third.
• D. CN VII (facial nerve / chorda tympani) provides taste and general sensation to the ANTERIOR 2/3 of the tongue — not the posterior third.