Anatomy Atlas

Muscles of facial expression

Musculi faciei
Also: Mimetic muscles
MuscleHigh-yielddraftNeuro

Thin subcutaneous muscles derived from the second pharyngeal arch and supplied by the facial nerve (CN VII). Their pattern of weakness distinguishes a peripheral facial palsy (Bell palsy) from a stroke.

Core anatomy

Location

In the superficial fascia of the face, scalp and neck; most insert into the skin.

Group

Second pharyngeal arch derivatives

Origin

Mostly from bones of the face or fascia (e.g. orbicularis oculi from the medial orbital margin; zygomaticus major from the zygomatic bone; buccinator from the alveolar processes and pterygomandibular raphe).

Insertion

Mostly into the skin and each other (e.g. modiolus at the angle of the mouth), which is why they move the skin.

Innervation

Facial nerve (CN VII) — its five terminal branches leave the parotid gland: temporal, zygomatic, buccal, marginal mandibular and cervical ("To Zanzibar By Motor Car"). Also stapedius, stylohyoid and the posterior belly of digastric.

Blood supply

Facial, superficial temporal and transverse facial arteries (branches of the external carotid artery).

Action
  • Orbicularis oculi: closes the eyelids (blinking, tight closure)
  • Frontalis (occipitofrontalis): raises the eyebrows, wrinkles the forehead
  • Orbicularis oris: closes and purses the lips
  • Buccinator: compresses the cheek (keeps food between the teeth; blowing)
  • Zygomaticus major: smiling; depressor anguli oris: frowning
  • Platysma: tenses the skin of the neck, depresses the mandible
Relations

The upper face (frontalis, upper orbicularis oculi) receives bilateral cortical input, whereas the lower face receives mainly contralateral input — the key to localizing facial weakness.

Mentioned in

Generated automatically from links in other entries.

Upper vs lower motor neuron facial palsyEach facial nucleus in the pons has an upper part supplying the forehead and a lower part supplying the lower face. The upper part receives corticobulbar fibers from both motor cortices; the lower part only from the opposite cortex. An upper motor neuron lesion in the right cortex or internal capsule therefore weakens only the lower left face, sparing the forehead, which still receives input from the left cortex. A lesion of the left facial nerve itself, as in Bell palsy, weakens the whole left side of the face including the forehead.ABLeft motor cortexRight motor cortexFacial nucleus — forehead part(input from both sides)Facial nucleus — lower face part(input from the opposite side only)Cortex or internal capsuleLeft facial nervePons (patient's left ← → right)UMN lesion (A)Lower face weakforehead sparedLMN lesion (B)Whole half of theface weakFaces seen from the front · shaded = weak (patient's left)

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Upper vs lower motor neuron facial palsy. The forehead part of each facial nucleus gets corticobulbar input from both cortices; the lower-face part only from the opposite cortex. A stroke in the cortex or internal capsule (A) therefore weakens the opposite lower face and spares the forehead. A facial nerve lesion such as Bell palsy (B) weakens the whole of that side of the face, forehead included. Forehead involved = peripheral; forehead spared = central.
Original schematic, created for this atlas.
Lateral view of the muscles of facial expression, the epicranius (occipitofrontalis) with the galea aponeurotica, and the superficial neck muscles
Muscles of facial expression and the superficial neck muscles.
Henry Vandyke Carter, Gray's Anatomy of the Human Body, 20th ed. (1918), Fig. 378. Source · Public domain (Public domain in the US: published before January 1, 1931 (per Wikimedia Commons))

Clinical correlations

Bell palsy (peripheral facial nerve palsy) PANCE

Mechanism / lesion

Idiopathic (often attributed to HSV reactivation) swelling of the facial nerve in the facial canal — a lower motor neuron lesion.

Classic presentation

Sudden unilateral weakness of the whole face, including the forehead (can't raise the eyebrow or close the eye), drooping mouth, loss of nasolabial fold; may have hyperacusis, loss of taste to the anterior two-thirds of the tongue, and decreased tearing. Treat with oral corticosteroids within 72 hours (± antivirals) and eye protection.

Central (upper motor neuron) facial palsy PANCE

Mechanism / lesion

Stroke or tumor affecting the corticobulbar fibers above the facial nucleus.

Classic presentation

Weakness of the lower face only on the opposite side, with the forehead spared (bilateral upper-face innervation), usually with other deficits (arm weakness, aphasia).

Other causes of peripheral facial palsy PANCE

Mechanism / lesion

Ramsay Hunt syndrome (VZV — vesicles in the ear canal), Lyme disease (may be bilateral), parotid tumors or surgery, temporal bone fracture, otitis media, sarcoidosis.

Classic presentation

Look in the ear for vesicles, ask about tick exposure, and palpate the parotid; bilateral palsy suggests Lyme, Guillain–Barré or sarcoidosis.

High-yield PANCE pearls

  • Forehead involved = peripheral (Bell); forehead spared = central (stroke).
  • Bell palsy → prednisone within 72 h + eye care (lubricant, taping).
  • Vesicles in the ear + facial palsy → Ramsay Hunt (VZV).
  • Bilateral facial palsy → Lyme, Guillain–Barré, sarcoidosis.
  • Facial nerve branches: Temporal, Zygomatic, Buccal, Marginal mandibular, Cervical.

Imaging anatomy

CT

Head CT if stroke is suspected (forehead-sparing weakness, other deficits); temporal bone CT for trauma.

MRI

MRI with contrast for atypical or progressive palsy, recurrence, or no recovery after about 3 months (tumor along the nerve, e.g. parotid or cerebellopontine angle).

Physical exam

Surface landmarks

The facial nerve branches fan out from the anterior border of the parotid gland.

Strength / function testing

Ask the patient to raise the eyebrows (frontalis), close the eyes tightly against resistance (orbicularis oculi), smile and show the teeth, puff the cheeks (buccinator), and tense the neck (platysma). Look for Bell phenomenon (the eye rolls up when trying to close). Check taste, hearing (hyperacusis) and the ear canal.

Self-quiz

Q1.

A 35-year-old woman wakes with drooping of the right side of her face. She cannot raise her right eyebrow or fully close her right eye. There are no other neurologic deficits and the ear canal is normal. What is the best treatment?

Show answer

B

Involvement of the forehead indicates a peripheral (lower motor neuron) lesion — Bell palsy. Corticosteroids within 72 hours improve recovery; protect the eye from exposure keratitis. tPA is for ischemic stroke, which spares the forehead.

Q2.

Why is the forehead spared in a stroke causing facial weakness?

Show answer

B

The part of the facial nucleus supplying the upper face receives input from both cerebral hemispheres, so a unilateral cortical lesion spares the forehead. The lower face receives mainly contralateral input.

Q3.

A 60-year-old has painful vesicles in the right ear canal and new weakness of the whole right side of the face. What is the diagnosis?

Show answer

E

Ramsay Hunt syndrome is reactivation of varicella-zoster in the geniculate ganglion, causing facial palsy with vesicles in the ear canal. Always look in the ear in a facial palsy.

Q4.

Bilateral peripheral facial palsy should raise suspicion for which conditions?

Show answer

A

Bell palsy is almost always unilateral. Bilateral facial palsy suggests Lyme disease, Guillain–Barré syndrome or sarcoidosis.

Q5.

Which nerve supplies the buccinator muscle?

Show answer

D

Buccinator is a muscle of facial expression (2nd arch), supplied by the buccal branch of the facial nerve. The long buccal nerve of V3 is purely sensory to the cheek.

Flashcards

See also