Final answer:
When a doctor encourages a patient to show their teeth or raise their eyebrows and close their eyes, they are testing the functions of the cranial nerves associated with facial expressions and eye movements.
Step-by-step explanation:
When a doctor encourages a patient to show their teeth or raise their eyebrows and close their eyes, they are testing the functions of the cranial nerves associated with facial expressions and eye movements. Specifically, they are testing the functions of the facial nerve (cranial nerve VII) for facial expressions like smiling, the oculomotor nerve (cranial nerve III) for raising the eyebrows, and the oculomotor and facial nerves for closing the eyes.
These tests help assess the patient's neurological function and can indicate the presence of any deficits or abnormalities in the cranial nerves. For example, if a patient is unable to raise their eyebrows or close their eyes on one side of their face, it may suggest damage to the corresponding cranial nerve on that side.