The facial nerve is a cranial nerve. It plays a major role in the control and sensation of facial muscles and the sensation of taste.
Some viruses can affect the facial nerve, resulting in a loss of the ability to control the facial muscles. Physicians check the health of the facial nerve by asking the patient to make exaggerated facial movements such as pursing the lips and puffing out the cheeks. The patient should be able to do this easily and there should be no noticeable asymmetry between the left and right sides.