5 Affected Muscles
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Frontalis
Action: Elevation of the eyebrows; wrinkles the forehead
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Orbicularis Oculi
Action: Closes the eyelids (i.e., blinking, protecting the eye)
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Platysma
Action: Pulling down the mandible; opening of the mouth; pulling the corners of the lips
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Orbicularis Oris
Action: Closes and puckers the lips (e.g., speech, blowing, and eating)
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Buccinator
Action: Cheek compression (e.g., chewing, preventing food from accumulating between the cheeks and teeth)
Mechanism
Inflammation/viral infection causes compression or damage to the facial nerve as it travels through the facial canal in the temporal bone. This affects the motor signals to the muscles of facial expression, leading to unilateral paralysis (i.e., weakness of the facial muscles on the affected side). Since the facial nerve carries motor innervation to all the muscles of facial expression, disruption of this nerve results in the characteristic drooping of the face.
Other Symptoms
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Inability to close the eye
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Inability to raise the eyebrow
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Drooling
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Speech difficulties
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Hyperacusis