Affected Muscles and Actions:
1. Frontalis: Raises eyebrows, wrinkles forehead.
2. Orbicularis Oculi: Closes eyelids, assists in blinking and squinting.
3. Zygomaticus Major: Elevates corners of mouth (smiling).
4. Orbicularis Oris: Closes and protrudes lips.
5. Buccinator: Compresses cheeks (blowing and chewing).
Mechanism of Weakness:
Bell's palsy is a condition resulting from inflammation of the facial nerve. This inflammation causes the compression or irritation of the facial nerve, which impairs its ability to send signals to the muscles it innervates. Ultimately, this leads to impaired muscle control on one side of the face.
Other Symptoms:
- Difficulty closing the eye: Weakness of Orbicularis Oculi leads to difficulty in closing eyelid fully on affected side, which can lead to dry eye or excessive tearing.
- Loss of nasolabial fold: The crease from the nose to the mouth diminishes or disappears due to weakness in the zygomaticus major and other facial muscles.
- Impaired speech: Difficulty with pronouncing certain sounds, especially those requiring lip movement (e.g., "p," "b," "m").
- Drooling: Caused by weakness in the orbicularis oris, affecting saliva and food control.
- Changes in taste: Loss of taste on the front two-thirds of the tongue if the facial nerve’s chorda tympani is affected.
- Possible increased sensitivity to sound (hyperacusis): Increased sensitivity to sound due to paralysis of the stapedius muscle in the middle ear.