Which nerve innervates the muscles of mastication?

• A. Trigeminal nerve, mandibular division (CN V3)
• B. Facial nerve (CN VII)
• C. Glossopharyngeal nerve (CN IX)
• D. Hypoglossal nerve (CN XII)

Answer: (A)

Muscles used for chewing are innervated by the mandibular division of the trigeminal nerve. This division (CN V3) carries the motor fibers that supply the primary masticatory muscles—the masseter, temporalis, and the medial and lateral pterygoids. These muscles arise from the first pharyngeal arch, and their jaw-closing actions require motor input that travels with V3. In addition, V3 gives motor supply to the mylohyoid and the anterior belly of the digastric, which assist jaw movements. The other nerves listed have different roles: the facial nerve controls facial expression muscles; glossopharyngeal nerve supplies a pharyngeal muscle and parasympathetic fibers to the parotid; and the hypoglossal nerve moves tongue muscles. So the nerve that innervates the muscles of mastication is CN V3.