Which cranial nerve provides motor innervation to the tongue muscles?

• A. Hypoglossal nerve (XII)
• B. Trigeminal nerve (V)
• C. Glossopharyngeal nerve (IX)
• D. Vagus nerve (X)

Answer: (A)

Motor control of the tongue muscles comes from the hypoglossal nerve, the twelfth cranial nerve. It supplies all intrinsic tongue muscles and most extrinsic ones (genioglossus, hyoglossus, and styloglossus). The palatoglossus, however, is innervated by the vagus nerve via the pharyngeal plexus. Clinically, a lesion to the hypoglossal nerve causes weakness on the affected side, so the tongue deviates toward that side when you try to protrude it, with possible atrophy and fasciculations. The other nerves listed have different motor targets: trigeminal controls muscles of mastication (and some muscles involved in the palate), glossopharyngeal mainly handles stylopharyngeus and salivary/parotid functions, and vagus supplies the palatoglossus along with many pharyngeal and laryngeal muscles.