Bell's palsy is caused by damage to the facial (VII) nerve due to possible causes such as disease, infection, or surgical damage. The damage to the facial (VII) nerve inhibits the transfer of action impulses to the following facial muscles along with their actions:
Muscle: Occipitofrontalis
Action: Wrinkles forehead, draws scalp anteriorly, and raises eyebrows
Muscle: Orbicularis oculi
Action: Closes eye
Muscle: Orbicularis oris,
Action: Shapes, compresses, closes, and protrudes lips
Muscle: Buccinator
Action: Mastication, presses cheek, and draws corner of mouth laterally
Muscle: Platysma
Action: Draws lower lip inferiorly and posteriorly, and depresses mandible
Furthermore, due to the facial muscle weakness of the patient, they may have trouble consuming food and liquids, drooling, and a dry left eye.