Which branch provides motor innervation to muscles of mastication?

• A. CN V1
• B. CN V2
• C. CN V3
• D. CN X

Answer: (C)

The key idea is that the muscles used for chewing get their motor drive from the motor fibers of the trigeminal nerve, specifically its mandibular division. This division is unique among the three trigeminal branches because it carries motor as well as sensory fibers, while the ophthalmic (V1) and maxillary (V2) divisions are purely sensory. The mandibular division innervates the muscles of mastication—masseter, temporalis, and the medial and lateral pterygoids—and also provides motor input to the mylohyoid and the anterior belly of the digastric via its branches. The vagus nerve does not control these muscles. So the branch delivering motor innervation to the muscles of mastication is the mandibular division of the trigeminal nerve.