The zygomaticus major is the primary smiling muscle, running obliquely from the cheekbone to the corner of the mouth and producing the upward lateral movement of the mouth angle that creates a genuine smile. It is the most important of the muscles of facial expression for social communication. Facial nerve palsy from any cause paralyses the zygomaticus major on the affected side, producing a flattened smile and asymmetric facial movement that can severely impact social interaction and psychological wellbeing.
| Origin | Zygomatic bone anterior to the zygomaticotemporal suture |
|---|---|
| Insertion | Angle of the mouth, blending with the orbicularis oris and depressor anguli oris |
| Nerve Supply | Zygomatic and buccal branches of the facial nerve (CN VII) |
| Blood Supply | Facial artery |
| Actions | Draws the angle of the mouth upward and laterally to produce a smile |
|---|
Its oblique course from the zygomatic bone to the mouth angle creates the nasolabial fold and draws the cheek upward during smiling, a movement universally recognised as expressing positive emotion across cultures.
Facial nerve palsy (Bell palsy, stroke, or parotid tumour invasion) produces ipsilateral zygomaticus major paralysis causing an inability to smile symmetrically on the affected side. Reinnervation after facial nerve reconstruction using cable grafts or nerve transfers targets the zygomaticus branch specifically because its function is most socially important. Botulinum toxin injection into the zygomaticus major for aesthetic facial slimming or asymmetry correction is increasingly performed.
The zygomaticus major is palpable as an oblique band running from the cheekbone toward the mouth angle, becoming firm during smiling or resisted mouth corner elevation.
Paralysis of the zygomaticus major and other facial muscles from facial nerve injury at any level, producing asymmetric smile, eye closure difficulty, and significant psychosocial impact managed with reinnervation procedures and facial retraining.
