Some muscles affected by Bell’s Palsy are:
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Frontalis - responsible for elevating the eyebrows
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Depressor Angularis Oris - pulls the angle of the mouth inferolaterally
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Platysma - draws the corners of the mouth inferiorly and widens (commonly for expressing sadness)
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Orbicularis Oculi - closes eyelids
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Buccinator - compresses the cheeks against the teeth and is used in acts such as blowing
Mechanism of Muscle Weakness:
Bell’s palsy is an unexplained episode of facial muscular paralysis or weakening. Over the course of 48 hours, it gets worse suddenly. This disorder is brought on by facial nerve injury, specifically the 7th cranial nerve. Pain and discomfort are more common on one side of the face or head.
Other Symptoms:
Additional symptoms include loss of feeling in the face, headache, tearing, drooling, loss of the sense of taste on the front two-thirds of the tongue, hypersensitivity to sound in the affected ear (hyperacusis), and inability to close the eye on the affected side of the face.
Reference: hopkins.medicine.org