The following are the 5 muscles affected and their corresponding actions:
- Frontalis – draws the scalp anteriorly, raises eyebrows, and wrinkles skin of the forehead horizontally
- Orbicularis oculi – closes the eye
- Orbicularis oris – closes and protrudes lips, compresses lips against teeth, and shapes lips during speech
- Buccinator – presses cheeks against teeth and lips, draws corner of the mouth laterally, and assists in chewing
- Platysma – draws the outer part of the lower lip inferiorly and posteriorly, and depresses the mandible
His muscle weakness results from the damage to the facial (VII) nerve. Because of this, the entire side of his face is drooped. He cannot close his eye, wrinkle his forehead, or move the lips on the affected side. Moreover, as a result of facial muscle weakness, the patient could exhibit drooling and difficulty in swallowing.