Final answer:
The facial nerve is assessed by asking the patient to puff out their cheeks and smile, which tests the control of muscles responsible for facial expressions.
Step-by-step explanation:
The cranial nerve being assessed when a patient is asked to puff out their cheeks and then smile really big is the facial nerve. The facial nerve controls the muscles of facial expression, including actions such as smiling, frowning, and puffing the cheeks.
In addition to assessing facial symmetry and movement, this nerve examination is crucial to identify any potential deficits that might indicate neurological problems. The buccinator muscle, which is integral for actions like blowing and sucking, is controlled by the facial nerve.
During a medical examination, the test might involve resistance, like having a patient attempt to keep their eyes closed while the examiner tries to open them, to ensure proper muscle function. This helps the healthcare professional determine the strength and functioning of the facial nerve and any possible issues that might be present.