(a) Occipitofrontalis
Action: Draws scalp anteriorly, raises eyebrows, and wrinkles skin of forehead horizontally
(b) Orbicularis oculi
Action: Closes eye
(c) Orbicularis oris
Action: Closes lips, protrudes lips, compresses lips against teeth, shapes lips during speech
(d) Buccinator
Action: Compresses cheek against teeth and gums, draws corner of mouth laterally, assists in chewing by keeping food between the teeth
(e) Platysma
Action: Draws lower lip and angle of mouth downward
Mechanism of Muscle Weakness: Suspected to be caused by an inflammation in the facial nerves resulting in muscle weakness (could be caused by an ear infection, ear surgery that damages facial nerve, or infection by the herpes simplex virus).
Other symptoms: Drooling, pain around the jaw or in or behind ear of affected side, increased sensitivity to sound on affected side, headache, loss of taste, and changes in amount of saliva and tears produced
References:
Cleveland Clinic (n.d.). Bell’s Palsy. Cleveland Clinic. Retrieved from https://my.clevelandclinic.org/health/diseases/5457-bells-palsy#:~:text=is%20Bell%27s%20palsy%3F-,Bell%27s%20palsy%20is%20a%20condition%20that%20causes%20temporary%20facial%20paralysis,you%20can%27t%20fully%20close
Mayo Clinic (2022, May 4). Bell’s Palsy. Mayo Clinic. https://www.mayoclinic.org/diseases-conditions/bells-palsy/symptoms-causes/syc-20370028
Tortora, G. J. & Derrickson, B. (2017). Principles of anatomy & physiology (15th ed.).