The primary functions of the zygomatic branch of the facial nerve are to control muscles involved in eye closure and elevation of the corners of the mouth (smiling).
Detailed Explanation
The zygomatic branch is a key division of the facial nerve (cranial nerve VII). After the facial nerve exits the stylomastoid foramen, it branches out to control various muscles of facial expression. The zygomatic branch specifically innervates muscles located around the zygomatic bone (cheekbone), playing a vital role in these facial movements:
- Eye Closure: The zygomatic branch innervates the orbicularis oculi muscle, which is responsible for closing the eyelids. This action is crucial for protecting the eye from injury and keeping it lubricated.
- Smiling and Cheek Elevation: The zygomatic branch innervates the zygomaticus major and minor muscles. These muscles pull the corners of the mouth upward and outward, creating a smile. They are also involved in elevating the cheeks. Notably, the nerve to zygomaticus major, arising from the zygomatic branch, innervates the zygomaticus major muscle and, importantly, also supplies the palpebral portion of the orbicularis oculi.
Muscles Innervated
Here's a breakdown of the key muscles innervated by the zygomatic branch:
| Muscle | Function | Facial Expression |
|---|---|---|
| Orbicularis Oculi | Closes eyelids, involved in blinking and squinting | Protection, emotion |
| Zygomaticus Major | Elevates and retracts the corner of the mouth | Smiling, laughing |
| Zygomaticus Minor | Elevates the upper lip | Smiling, showing teeth |
Clinical Significance
Damage to the zygomatic branch, such as from trauma or surgery, can result in:
- Difficulty closing the eye: This can lead to dry eye, corneal irritation, and potentially corneal damage.
- Facial asymmetry when smiling: One side of the mouth may not elevate as much as the other, resulting in a crooked smile.
- Weakness in cheek elevation.
