In a patient with Down syndrome, which nerve controls the tongue movements that contribute to the characteristic tongue protrusion?

Correct answer: A. Hypoglossal nerve (CN XII)

• A. CORRECT. The HYPOGLOSSAL NERVE (CN XII) supplies all intrinsic tongue muscles and all extrinsic muscles except palatoglossus. In Down syndrome the apparent tongue protrusion is largely RELATIVE macroglossia — generalised hypotonia (including the CN XII-innervated musculature) combined with a small maxilla and reduced oropharyngeal volume — rather than a truly enlarged tongue.
• B. CN IX carries taste and general sensation from the posterior third of the tongue and motor supply to stylopharyngeus. It does not move the tongue body.
• C. CN VII carries taste from the anterior two-thirds via chorda tympani and motor supply to facial expression — not tongue movement.
• D. V3 provides general SENSATION to the anterior two-thirds via the lingual nerve, but no motor supply to the tongue.

Note: Palatoglossus is the exception — it is supplied by the pharyngeal plexus (CN X), not CN XII.