A patient shows drooping of the corner of the mouth but CAN still close the eye and wrinkle the forehead on the affected side. Which muscle is involved and what nerve mediates it?

Correct answer: A. Orbicularis oris, mediated by the facial nerve (CN VII)

• A. Correct. The drooping mouth corner involves orbicularis oris, a muscle of facial expression supplied by CN VII.
• B. Incorrect. The masseter is a muscle of mastication (CN V3) and is not responsible for mouth-corner droop.
• C. Incorrect. Orbicularis oculi closes the eye and is supplied by CN VII (not CN III); here eye closure is preserved.
• D. Incorrect. The buccinator is supplied by CN VII, not CN IX, and is not the muscle drooping the lip.

Note: Preserved forehead/eye function points to a central (upper motor neuron) lesion sparing the upper face; the lower facial muscles are still supplied by CN VII. A lower motor neuron lesion (Bell's palsy) would also impair eye closure.