Which cranial nerve is responsible for mastication?

• A. Facial nerve (VII)
• B. Glossopharyngeal nerve (IX)
• C. Vagus nerve (X)
• D. Trigeminal nerve (V)

Answer: (D)

Chewing is controlled by the motor part of the trigeminal nerve, specifically its mandibular division. This branch sends motor signals to the four muscles of mastication—the masseter, temporalis, and the two pterygoids—which handle the opening, closing, and grinding movements of the jaw. The trigeminal nerve also carries facial-skin sensation, but its motor portion to these jaw muscles is what drives mastication. The other nerves listed have different roles: the facial nerve mainly moves muscles of facial expression; the glossopharyngeal nerve handles taste and some pharyngeal muscles; the vagus nerve governs pharyngeal and laryngeal muscles and autonomic functions.