Which cranial nerve governs sensation from the forehead and face and the clenching of the jaw?

• A. Olfactory
• B. Optic
• C. Trigeminal
• D. Vagus

Answer: (C)

The key idea is which cranial nerve provides facial sensation and controls the muscles used to bite and clench the jaw. The trigeminal nerve is the primary sensory nerve for the face, with three branches that cover the forehead and the rest of the face, carrying touch, pain, and temperature signals. It also carries motor fibers to the muscles of mastication, such as the masseter and temporalis, enabling jaw clenching and chewing. The other nerves listed don’t handle both facial sensation and jaw-closing muscles: olfactory is smell, optic is vision, and vagus controls many autonomic functions and some throat muscles, not facial sensation or jaw movement.