Affected Muscles and Their Actions
1. Frontalis
- Action: Elevates the eyebrows and wrinkles the forehead.
2. Orbicularis Oculi
- Action: Closes the eyelids (e.g., blinking and protecting the eye).
3. Platysma
- Action: Pulls down the mandible, opens the mouth, and pulls the corners of the lips.
4. Obicularis Oris
- Action:: Closes and puckers the lips (e.g., for speech, blowing, and eating).
5. Buccinator
- Action: Compresses the cheek (e.g., during chewing and preventing food from accumulating between the cheeks and teeth).
Mechanism
Inflammation or viral infection can compress or damage the facial nerve as it travels through the facial canal in the temporal bone. This disruption affects the motor signals to the facial expression muscles, leading to unilateral paralysis (weakness on one side of the face). Since the facial nerve innervates all facial expression muscles, its impairment causes the characteristic drooping of the facts.
Other Symptoms
1. Inability to close the eye.
2. Inability to raise the eyebrow.
3. Drooling.
4. Speech difficulties.
5. Hyperacusis.