The Two Most Important Facial Nerve Branches for Facial Movement
The temporal (frontal) branch and the marginal mandibular branch are the two most critical facial nerve branches because they control eye closure and mouth/smile function respectively—the temporal branch innervates the frontalis and orbicularis oculi muscles (enabling forehead elevation and eye protection), while the marginal mandibular branch innervates the orbicularis oris and lower facial muscles (enabling mouth closure, smiling, and speech articulation). 1, 2, 3
Temporal (Frontal) Branch Functions
The temporal branch is functionally critical because it provides motor innervation to:
- Orbicularis oculi muscle - Essential for eye closure and corneal protection, preventing permanent corneal damage from exposure keratitis 1, 3
- Frontalis muscle - Controls forehead elevation and eyebrow raising, critical for facial expression and communication 4, 2
- Corrugator supercilii muscle - Enables frowning and medial brow depression 4
Clinical significance: Loss of temporal branch function results in inability to close the eye completely, requiring immediate eye protection measures including lubricating drops, ointment, and eye taping to prevent irreversible corneal damage 1. The temporal branch courses approximately 2.85 cm superior and 2.54 cm lateral to the lateral canthus as it enters the orbicularis oculi muscle 5.
Marginal Mandibular Branch Functions
The marginal mandibular branch is equally critical because it innervates:
- Orbicularis oris muscle - Controls mouth closure, lip pursing, and articulation for speech 2, 3
- Lower facial muscles - Enables smiling, showing teeth, and lower lip depression 2
- Depressor anguli oris - Controls downward mouth corner movement 2
Clinical significance: The marginal mandibular branch was distributed to the orbicularis oris muscle in all 25 cases examined in anatomical studies, confirming its consistent and essential role 3. Loss of this branch results in inability to smile symmetrically, with the mouth pulling only toward the unaffected side, and causes visible drooping of the mouth corner 1.
Anatomical Considerations
Both branches run within specific fascial planes that surgeons must respect:
- The temporal and zygomatic branches course between the deep layer of the superficial temporal fascia and the superficial layer of the deep temporal fascia 4, 6
- The frontal branch of the superficial temporal artery serves as a critical landmark—dissection inferior to this vessel risks injury to the temporal nerve branches 6
- After exiting the stylomastoid foramen, the facial nerve traverses the parotid gland where it divides into five terminal branch groups: temporal, zygomatic, buccal, mandibular, and cervical 2
Why These Two Branches Are Most Important
Eye protection and facial communication represent the most functionally significant outcomes:
- Temporal branch loss threatens vision through corneal exposure, requiring immediate intervention 1
- Marginal mandibular branch loss eliminates the ability to smile, speak clearly, and maintain oral competence—functions essential for quality of life and social interaction 1, 3
The zygomatic and buccal branches, while important, demonstrate more anatomical redundancy and compensation. The zygomatic branch was distributed to both orbicularis oculi and orbicularis oris muscles in some cases, and the buccal branch showed variable distribution patterns 3. In contrast, the temporal branch consistently innervated the orbicularis oculi in all cases, and the marginal mandibular branch consistently innervated the orbicularis oris in all cases 3.