Which cranial nerve provides motor innervation to the intrinsic and extrinsic muscles of the tongue, excluding the palatoglossus?

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

Answer: (A)

Motor control of the tongue is provided primarily by a single cranial nerve that delivers somatic motor innervation to the intrinsic tongue muscles and all extrinsic tongue muscles except one. The intrinsic muscles—such as the longitudinal, transverse, and vertical groups—and the extrinsic muscles like genioglossus, hyoglossus, and styloglossus are chiefly innervated by this nerve as it courses to the tongue. The one exception is palatoglossus, which originates from the soft palate and is innervated not by this nerve but by the pharyngeal branch of the vagus nerve. So, the nerve responsible for the bulk of tongue motor function is the hypoglossal nerve. The other nerves play different roles: the trigeminal nerve handles chewing muscles and facial sensation (and contributes sensory innervation to the anterior two-thirds of the tongue), the glossopharyngeal nerve provides motor to stylopharyngeus and taste/sensation to the posterior tongue, and the vagus nerve supplies muscles of the palate and pharynx (including palatoglossus).