Head & Neck Anatomy · Surgery

Muscles of Facial Expression

All muscles of facial expression derive from the second pharyngeal arch and are all supplied by CN VII. They insert into skin, conveying emotion.

✦ The Mnemonic

"Five Regions Of Zest Build Personality"

Five groups — all innervated by CN VII branches (Temporal, Zygomatic, Buccal, Marginal mandibular, Cervical)

F Frontalis / Occipitofrontalis Raises eyebrows; CN VII temporal branch

R Orbicularis Oculi Closes eye — orbital (tight) and palpebral (blink); temporal + zygomatic

O Orbicularis Oris Closes and purses lips; buccal branch

Z Zygomaticus Major + Minor Draws corner of mouth up and out — smiling; zygomatic + buccal

B Buccinator Compresses cheek against teeth; buccal branch

P Platysma Depresses mandible and lower lip; tenses neck skin; cervical branch

📚 Clinical Breakdown

The five CN VII branches: "Two Zebras Bit My Cat" — Temporal, Zygomatic, Buccal, Marginal mandibular, Cervical. These emerge from the parotid gland. The marginal mandibular branch runs at the inferior mandibular border — controls lower lip depressors; most commonly injured in submandibular surgery.

Bell's palsy (idiopathic LMN CN VII): complete ipsilateral facial weakness including the forehead. Eye cannot close → corneal exposure keratopathy risk. Prednisolone within 72 hours significantly improves recovery. Add antivirals if Ramsay Hunt syndrome suspected.

SMAS (superficial musculoaponeurotic system): the fibromuscular layer investing the muscles of facial expression — the plane of dissection in facelifts and parotidectomy.

All innervated by CN VII — 5 branches (TZBMC)

Forehead spared in UMN lesion — bilateral cortical representation

Forehead involved in LMN lesion — Bell's palsy, parotid tumour

Marginal mandibular risk Jaw margin surgery → lower lip drooping

⭐ Clinical Pearl

Ramsay Hunt syndrome: VZV reactivation in the geniculate ganglion. Causes LMN facial palsy + vesicular rash in the external auditory meatus and/or hard palate. CN VIII involvement adds sensorineural hearing loss and vertigo. Worse prognosis than Bell's palsy. Treat with aciclovir + prednisolone.

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