Five muscles affected and their associated actions:
1. Frontalis: Draws scalp anteriorly, raises eyebrows, and wrinkles skin of forehead horizontally.
2. Orbicularis oculi: Closes eye.
3. Orbicularis oris: Closes and protrudes the lips, compresses lips against teeth, and shapes lips.
4. Buccinator: Presses cheeks against teeth and lips, draws corner of mouth laterally; and assists in mastication (chewing)
5. Platysma: Draws outer part of lower lip inferiorly and posteriorly; depresses mandible.
Mechanism of muscle weakness:
Bell’s palsy is caused by damage or disease of the facial nerve (cranial nerve VII). When this happens, the signals that normally stimulate the facial muscles are disrupted, leading to muscle paralysis or weakness in one side of the face.
Other symptoms associated with facial muscle weakness:
Patient AM cannot wrinkle the forehead, close the eye, or pucker the lips on the affected side. Drooling, altered taste sensation, increased sensitivity to sound, and difficulty in swallowing are some of the other symptoms of Bell’s palsy.