5 muscles:
1. Frontalis - Draws scalp anteriorly, raises eyebrows and wrinkles skin of forehead horizontally as in look of surprise
2. Orbicularis oris - Closes and protrudes lips, as in kissing; compresses lips against teeth; and shapes lips during speech
3. Orbicularis oculi - Closes eye
4. Buccinator - Presses cheeks against teeth and lips, as in whistling, blowing, and sucking; draws corner of mouth laterally; and assists in mastication (chewing) by keeping food between the teeth (and not between teeth and cheeks).
5. Platysma - Draws outer part of lower lip inferiorly and posteriorly as in pouting; depresses mandible.
Mechanism of his muscle weakness: Caused by damage or disease of the facial
(VII) nerve, it is the unilateral paralysis of the muscles of facial expression.
Other symptoms: Cannot wrinkle forehead, pucker the lips or close the eye on the affected side, drooling, difficulty in swallowing
References:
Tortora, G. J., & Derrickson, B. (2017). Principles of anatomy and physiology (15th ed., p. 340). Wiley.