5 muscles affected and their actions
Orbicular oris - closes and protrudes lip
Orbicularis oculi - Closes eye
Levator anguli oris - Draws angle of mouth laterally and superiorly
Levator labii superioris - Raises upper lip
Corrugator supercilii - draws eyebrow inferiorly, wrinkles skin of forehead
Mechanism of muscle weakness: Facial nerve has been damaged or been afflicted by a disease.
Other possible symptoms: Cannot wrinkle their forehead, close the eye, difficulty in swallowing and more
Reference:
Tortora, G. J., & Derrickson, B. (2017). Principles of anatomy & physiology. Fifteenth edition; Wiley Loose-Leaf Print Companion. Hoboken, New Jersey, John Wiley & Sons, Inc.