Which cranial nerve is involved in jaw clenching and jaw movement?

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

Answer: (C)

The main concept here is which cranial nerve supplies the muscles that move and clench the jaw. The jaw’s clenching and chewing actions are carried out by the muscles of mastication—the masseter, temporalis, and the pterygoid muscles—which are innervated by the mandibular division of the trigeminal nerve (the motor component of CN V). This makes trigeminal nerve the correct choice because it provides the motor control needed for jaw closure and movement.

The other nerves don’t serve this function. The facial nerve mainly controls muscles of facial expression and some other roles, not the muscles of mastication. The glossopharyngeal nerve handles taste and some pharyngeal actions, with limited motor roles that are not about jaw movement. The vagus nerve governs many muscles of the throat and more distant autonomic functions, not the jaw muscles.