Which nerve mediates taste to the posterior third of the tongue and also innervates salivary glands such as the parotid?

• A. Glossopharyngeal (CN IX)
• B. Facial (CN VII)
• C. Vagus (CN X)
• D. Hypoglossal (CN XII)

Answer: (A)

Taste from the posterior third of the tongue is carried by the glossopharyngeal nerve, and this same nerve provides parasympathetic (secretomotor) input to the parotid gland. The pathway for parotid secretion starts with preganglionic fibers in the inferior salivatory nucleus traveling with the tympanic nerve to the tympanic plexus, then via the lesser petrosal nerve to the otic ganglion. From there, postganglionic fibers hitch a ride with the auriculotemporal nerve (a branch of V3) to reach the parotid gland. So, this single nerve handles both taste for the back of the tongue and stimulating the parotid to produce saliva.

The other nerves don’t fit both roles: facial nerve handles taste from the front two-thirds of the tongue and parasympathetic supply to the submandibular and sublingual glands; vagus provides taste to areas like the epiglottis and other visceral innervation; hypoglossal mainly motor-controls tongue muscles.