Which cranial nerve has both sensory and motor components and is tested by asking a patient to smile, frown, and puff cheeks?

• A. Facial
• B. Trigeminal
• C. Glossopharyngeal
• D. Vagus

Answer: (A)

The nerve being tested is the one that powers most facial expressions. It’s a mixed nerve, meaning it has motor fibers that control the muscles of facial expression and sensory fibers that carry taste from the front of the tongue (and other small sensory functions). Asking a patient to smile, frown, and puff cheeks directly evaluates the motor function of these facial muscles, such as the orbicularis oris and other muscles around the mouth. If the patient shows weakness or asymmetry in these movements, it suggests facial nerve involvement. The other nerves mentioned don’t govern these facial expressions in the same way, so they aren’t the best fit for this specific motor testing.