Damage to the trigeminal nerve (CN V) would most directly affect which function?

• A. Reduced facial expression
• B. Reduced tongue mobility
• C. Reduced vocal fold movement
• D. Reduced mastication

Answer: (D)

Damage to the trigeminal nerve mainly disrupts the muscles that chew. The motor part of CN V, especially through the mandibular division, innervates the muscles of mastication—the masseter, temporalis, and the medial and lateral pterygoids. When this nerve is damaged, these muscles weaken or lose coordination, making chewing difficult and reducing bite force.

Other functions listed involve different nerves: facial expression is controlled by the facial nerve (CN VII), tongue movement by the hypoglossal nerve (CN XII), and vocal fold movement by branches of the vagus nerve (CN X). So the direct and most noticeable impact of CN V damage is on mastication.