Muscles
Brow
| Muscle | Origin | Insertion | Fibers | Action | Expression | AUs |
|---|---|---|---|---|---|---|
| Muscle: Frontalis | Origin: Galea aponeurotica | Insertion: Skin of eyebrows, blending with orbicularis oculi | Fibers: Vertical | Action: Raises brows | Expression: Horizontal forehead wrinkles — surprise | AUs: AU1, AU2 |
| Muscle: Corrugator supercilii | Origin: Medial end of superciliary arch | Insertion: Skin above middle of eyebrow | Fibers: Oblique, up-and-lateral | Action: Draws brows medially and down | Expression: Vertical glabellar furrows — frown | AUs: AU4 |
| Muscle: Depressor supercilii | Origin: Medial orbital rim near the frontal process of the maxilla | Insertion: Skin of the medial eyebrow | Fibers: Vertical | Action: Draws the medial eyebrow downward | Expression: Brow lowering — frown component | AUs: AU4 |
| Muscle: Procerus | Origin: Fascia over nasal bone and upper lateral nasal cartilage | Insertion: Skin of glabella between brows | Fibers: Vertical | Action: Pulls medial brow down | Expression: Transverse wrinkles over nose bridge | AUs: AU4 |
Eye
| Muscle | Origin | Insertion | Fibers | Action | Expression | AUs |
|---|---|---|---|---|---|---|
| Muscle: Orbicularis oculi | Origin: Medial orbital margin, medial palpebral ligament, lacrimal bone | Insertion: Lateral palpebral raphe; skin encircling orbit | Fibers: Concentric rings | Action: Orbital part squeezes eye region (AU6); palpebral part closes/tightens lids (AU7) | Expression: Cheek raise and lid tightening — genuine smile, squint | AUs: AU6, AU7 |
| Muscle: Levator palpebrae superioris | Origin: Lesser wing of sphenoid (orbit roof) | Insertion: Tarsal plate + skin of upper eyelid | Fibers: Anteroposterior | Action: Raises upper lid | Expression: Widened eyes — fear/surprise | AUs: AU5 |
Nose
| Muscle | Origin | Insertion | Fibers | Action | Expression | AUs |
|---|---|---|---|---|---|---|
| Muscle: Nasalis | Origin: Maxilla above incisors | Insertion: Aponeurosis across nasal bridge / nostril ala | Fibers: Transverse | Action: Compresses/flares nostrils | Expression: Nostril flare | AUs: AU9 |
Midface
| Muscle | Origin | Insertion | Fibers | Action | Expression | AUs |
|---|---|---|---|---|---|---|
| Muscle: Levator labii superioris alaeque nasi | Origin: Frontal process of maxilla | Insertion: Nostril ala + skin of upper lip | Fibers: Vertical | Action: Raises lip + flares nostril | Expression: Sneer/disgust | AUs: AU9 |
| Muscle: Levator labii superioris | Origin: Infraorbital margin of maxilla | Insertion: Skin/muscle of upper lip | Fibers: Vertical | Action: Raises upper lip, deepens nasolabial furrow | Expression: Disgust | AUs: AU10 |
Mouth
| Muscle | Origin | Insertion | Fibers | Action | Expression | AUs |
|---|---|---|---|---|---|---|
| Muscle: Zygomaticus major | Origin: Zygomatic bone (lateral surface) | Insertion: Modiolus at mouth corner | Fibers: Oblique down-medial | Action: Pulls lip corner up + lateral | Expression: Smile | AUs: AU12 |
| Muscle: Zygomaticus minor | Origin: Zygomatic bone, medial to major | Insertion: Upper lip medial to corner | Fibers: Oblique | Action: Elevates upper lip | Expression: Smiling/sad blend | AUs: AU11 |
| Muscle: Levator anguli oris | Origin: Canine fossa of maxilla | Insertion: Modiolus (deep to zygomaticus major) | Fibers: Vertical, deep layer | Action: Raises mouth corner directly | Expression: Sharp lip pull | AUs: AU13 |
| Muscle: Buccinator | Origin: Pterygomandibular raphe + alveolar processes of maxilla/mandible at molars | Insertion: Modiolus, blending into orbicularis oris | Fibers: Horizontal, deep layer | Action: Compresses cheek against teeth | Expression: Dimpling, blowing | AUs: AU14 |
| Muscle: Risorius | Origin: Fascia over masseter/parotid | Insertion: Modiolus | Fibers: Horizontal | Action: Retracts corner straight laterally | Expression: Grimace | AUs: AU20 |
| Muscle: Orbicularis oris | Origin: Maxilla + mandible near midline; fibers from modiolus muscles | Insertion: Skin and mucosa of lips | Fibers: Concentric sphincter | Action: Closes, tightens, protrudes lips | Expression: Pursed/pressed lips | AUs: AU23, AU24 |
Chin-Jaw
| Muscle | Origin | Insertion | Fibers | Action | Expression | AUs |
|---|---|---|---|---|---|---|
| Muscle: Depressor anguli oris | Origin: Oblique line of mandible | Insertion: Modiolus | Fibers: Converging upward | Action: Pulls corner down | Expression: Sadness | AUs: AU15 |
| Muscle: Depressor labii inferioris | Origin: Oblique line of mandible (anterior to DAO) | Insertion: Skin of lower lip | Fibers: Oblique up-medial | Action: Pulls lower lip down and lateral | Expression: Lower lip depression | AUs: AU16 |
| Muscle: Mentalis | Origin: Incisive fossa of mandible | Insertion: Skin of chin | Fibers: Vertical | Action: Raises + protrudes lower lip, wrinkles chin | Expression: Pout/doubt | AUs: AU17 |
Neck
| Muscle | Origin | Insertion | Fibers | Action | Expression | AUs |
|---|---|---|---|---|---|---|
| Muscle: Platysma | Origin: Fascia over pectoralis major and deltoid | Insertion: Lower border of mandible, skin of lower face, modiolus | Fibers: Vertical sheet | Action: Tenses neck skin, drags mouth corners down | Expression: Fear/exertion | AUs: AU21 |
Mastication
| Muscle | Origin | Insertion | Fibers | Action | Expression | AUs |
|---|---|---|---|---|---|---|
| Muscle: Masseter | Origin: Zygomatic arch | Insertion: Lateral surface of ramus and angle of mandible | Fibers: Vertical | Action: Elevates mandible | Expression: Clench | AUs: AU26 |
| Muscle: Temporalis | Origin: Temporal fossa | Insertion: Coronoid process of mandible | Fibers: Fan converging downward | Action: Elevates + retracts mandible | Expression: Jaw clench/drop | AUs: AU26 |