5 muscles affected by Bell’s palsy and their actions:
1. Orbicularis oculi
- Action: Closes eye.
2. Orbicularis oris
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Action: Closes and protrudes lips; compresses lips against teeth; and shapes lips during speech.
3. Buccinator
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Presses cheeks against teeth and lips; draws corner of mouth laterally; and assists in mastication (chewing) by keeping food between the teeth (and not between teeth and cheeks).
4. Occipitofrontalis (frontal belly)
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Draws scalp anteriorly, raises eyebrows, and wrinkles skin of forehead horizontally
5. Platysma
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Draws outer part of lower lip inferiorly and posteriorly; depresses mandible.
Mechanism of Muscle Weakness
Bell’s palsy, also known as facial paralysis, is a unilateral paralysis of the muscles of facial expression. It results from dysfunction or damage of cranial nerve VII, which connects your brain to the muscles that control facial expression (the nerve also is involved with taste and ear sensation). The nerve that controls facial muscles passes through a narrow corridor of bone on its way to the face. In Bell's palsy, that nerve becomes inflamed and swollen — usually related to a viral infection. Possible causes include inflammation of the facial nerve due to an ear infection, ear surgery that damages the facial nerve, or infection by the herpes simplex virus. In rare cases, Bell's palsy can affect both sides of your face.
Other symptoms the patient could exhibit as a result of facial muscle weakness:
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Drooling from one side of your mouth
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Difficulty closing an eyelid, which causes eye dryness
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Pain around the jaw or in or behind your ear on the affected side
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Increased sensitivity to sound on the affected side
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Headache
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A loss of taste
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Changes in the amount of tears and saliva you produce
References:
Bell’s Palsy. (n.d.). National Institute of Neurological Disorders and Stroke. https://www.ninds.nih.gov/health-information/disorders/bells-palsy
Bell’s palsy - Symptoms and causes - Mayo Clinic. (2022, May 4). Mayo Clinic. https://www.mayoclinic.org/diseases-conditions/bells-palsy/symptoms-causes/syc-20370028
Taylor, D. C. (2021, May 4). Bell Palsy (S. R. Benbadis, Ed.). Medscape. https://emedicine.medscape.com/article/1146903-overview
Tortora, G. & Derrickson, B. (2017). Chapter 11: The Muscular System. Principles of Anatomy and Physiology (15th ed.). Wiley.