Each of the following cranial nerves carries sensory fibres EXCEPT:

Correct answer: C. Hypoglossal (CN XII)

• A. The trigeminal nerve is the principal sensory nerve of the face and also carries motor fibres to the muscles of mastication in its mandibular division.
• B. Glossopharyngeal carries general sensation and taste from the posterior third of the tongue, sensation from the oropharynx, and baroreceptor input from the carotid sinus.
• C. CORRECT — this is the EXCEPT. The hypoglossal nerve is PURELY MOTOR. It supplies all the intrinsic tongue muscles and three of the four extrinsic muscles — genioglossus, hyoglossus and styloglossus — but carries no sensory fibres. Palatoglossus is the exception among tongue muscles, being supplied by the vagus via the pharyngeal plexus.
• D. The vagus carries sensation from the larynx, pharynx and thoracic and abdominal viscera in addition to its extensive motor and parasympathetic functions.

Note: The three purely motor cranial nerves are IV (trochlear), VI (abducens) and XII (hypoglossal) — plus III and XI if you count them as motor. Testing CN XII: ask the patient to protrude the tongue; it deviates TOWARD the side of a lower motor neuron lesion because the unopposed contralateral genioglossus pushes it across.