Five Affected Muscles
1. Frontalis
- Action: Raises the eyebrows and wrinkles the forehead; serves for facial expressions
2. Orbicularis oculi
- Action: Closes the eyelids and compresses lacrimal sac
3. Orbicularis oris
- Action: Closes and protrudes the lips
4. Buccinator
- Action: Compresses the cheeks against the teeth (used in chewing and blowing).
5. Zygomaticus major
- Action: Elevates the corners of the mouth
Mechanism of Muscle Weakness
Bell’s palsy induces inflammation of the facial nerve (cranial nerve VII), affecting the muscles used for facial expression. Due to this, it cannot properly send signals to the muscles it innervates, leading to facial droop. Other symptoms that can arise are:
1. Inability to close the eye properly
2. Increased sensitivity to sound in the affected side
3. Facial Asymmetry
4. Drooling