5 AFFECTED MUSCLES:
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OCCIPITOFRONTALIS
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ACTION: Draws the scalp anteriorly, raises the eyebrows, and horizontally wrinkles the skin of the forehead.
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PLATYSMA
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ACTION: Draws the outer part of the lower lip inferiorly and posteriorly, and depresses the mandible.
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BUCCINATOR
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ACTION: Draw the corner of the mouth laterally and press the cheeks against the teeth and lips.
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ORBICULARIS ORIS
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ACTION: Shuts and protrudes the lips, compresses the lips against the teeth, and shapes the lips during speech.
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ORBICULARIS OCULI
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ACTION: It blinks, then closes the eye.
MECHANISM OF MUSCLE WEAKNESS:
Bell's palsy is caused by cranial nerve VII dysfunction, connecting the brain to the muscles responsible for controlling facial expression (the nerve is also associated with taste and auditory sense). Rarely, both of one's facial sides may be affected by Bell's palsy.
OTHER SYMPTOMS DUE TO FACIAL MUSCLE WEAKNESS:
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Having trouble swallowing
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Drooling from one side of the mouth
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Difficulty closing an eyelid, resulting in eye dryness
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Pain or unusual sensations in the face
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Excessive tearing in one eye
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Difficulties with tasting
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Low threshold for loud noise
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Pain around the jaw and behind the ear
References:
Bell’s Palsy. (2023). National Institute of Neurological Disorders and Stroke. https://www.ninds.nih.gov/health-information/disorders/bells-palsy
Tortora, G. J., & Derrickson, B. (2017). Principles of ANATOMY & PHYSIOLOGY (15th ed.). Wiley.