CorpusHuman Anatomy
NervousNerve

Facial nerve (CN VII)

Nervus facialis

Also known as: CN VII, seventh cranial nerve, nervus intermedius, chorda tympani

A mixed nerve of the 2nd pharyngeal arch. It supplies the muscles of facial expression and stapedius, carries taste from the anterior two-thirds of the tongue, and is secretomotor to the lacrimal, submandibular and sublingual glands.

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Overview

NucleiFacial motor, superior salivatory, solitary tract (taste)
Exit from skullStylomastoid foramen (enters via internal acoustic meatus)
Facial canal length≈3 cm (narrowest: labyrinthine segment)
GangliaGeniculate (sensory); pterygopalatine & submandibular (parasympathetic)
Pharyngeal arch2nd

CN VII has a large motor root and a smaller nervus intermedius, which carries the sensory and parasympathetic fibres. Both emerge at the cerebellopontine angle (pontomedullary junction), medial to CN VIII. Its nuclei are:
• the facial motor nucleus in the caudal pons (SVE); its axons loop around the abducens nucleus to form the facial colliculus;
• the superior salivatory nucleus (GVE);
• the nucleus of the solitary tract (taste, SVA);
• the spinal trigeminal nucleus (GSA, a small area of the external ear).

The nerve enters the internal acoustic meatus and runs through the facial canal of the petrous temporal bone. Its segments are labyrinthine (the narrowest, and the commonest site of compression from swelling), tympanic and mastoid. At the geniculate ganglion, which contains the cell bodies of the taste fibres, the nerve turns sharply backward (the external genu) and gives off the greater petrosal nerve.

Within the canal it gives off the nerve to stapedius and the chorda tympani. The chorda tympani crosses the tympanic membrane, leaves through the petrotympanic fissure and joins the lingual nerve (V3). The facial nerve then exits through the stylomastoid foramen. It gives the posterior auricular nerve and branches to the posterior belly of digastric and stylohyoid. It then enters the parotid gland, where it divides into five terminal motor branches that run superficial to the retromandibular vein and external carotid artery. The parotid itself is supplied by CN IX, not VII.

Location

Cerebellopontine angle → internal acoustic meatus → facial canal (petrous temporal) → stylomastoid foramen → parotid gland → face.

Parts & subdivisions

  1. Functional components
    Both (mixed): SVE (branchial motor), GVE (parasympathetic), SVA (taste) and GSA. The nervus intermedius carries all the non-motor fibres.
  2. Clinical testing
    - Motor: raise the eyebrows (frontalis), close the eyes tightly against resistance, puff out the cheeks, show the teeth and whistle. Compare the nasolabial folds and look for incomplete eye closure; the eye rolls up on attempted closure (Bell phenomenon). • Corneal reflex: CN VII is the efferent limb. • Taste on the anterior 2/3 of the tongue. • Ask about hyperacusis (stapedius) and dry eye.
  3. Lesion localisation along the canal
    - Above the geniculate ganglion: all functions lost, including reduced lacrimation. • Between the geniculate ganglion and the nerve to stapedius: lacrimation spared, but hyperacusis and loss of taste. • Between the stapedius branch and the chorda tympani: taste lost, hearing normal. • At the stylomastoid foramen or in the parotid: facial weakness only.

Anatomy

Innervation

- Motor (SVE): muscles of facial expression (including orbicularis oculi, orbicularis oris, buccinator, occipitofrontalis and platysma), stapedius, the posterior belly of digastric and stylohyoid.
• Parasympathetic (GVE): lacrimal, nasal and palatine glands (pterygopalatine ganglion) and the submandibular and sublingual glands (submandibular ganglion).
• Taste (SVA): anterior 2/3 of the tongue (chorda tympani) and the palate (greater petrosal).
• General sensation (GSA): a small part of the auricle and external acoustic meatus.

Course

Pontomedullary junction → internal acoustic meatus (with VIII and the labyrinthine artery) → facial canal: labyrinthine segment → geniculate ganglion → tympanic segment (medial wall of the middle ear) → mastoid segment → stylomastoid foramen → enters the parotid gland → parotid plexus (pes anserinus) → five terminal branches fanning over the face.

Branches

In the facial canal:
• Greater petrosal nerve, from the geniculate ganglion. It joins the deep petrosal nerve to form the nerve of the pterygoid canal (Vidian nerve), which runs to the pterygopalatine ganglion. Its targets are the lacrimal gland and the nasal and palatine glands.
• Nerve to stapedius.
• Chorda tympani, which carries taste from the anterior 2/3 of the tongue and preganglionic fibres to the submandibular ganglion for the submandibular and sublingual glands.

After the stylomastoid foramen:
• Posterior auricular nerve (occipitalis and auricular muscles).
• Branches to the posterior belly of digastric and to stylohyoid.
• Five terminal branches: temporal, zygomatic, buccal, marginal mandibular, cervical.

Function

  • Facial expression, eye closure and blink (orbicularis oculi), lip seal and the buccinator role in chewing
  • Dampening of loud sounds (stapedius reflex)
  • Taste from the anterior 2/3 of the tongue
  • Lacrimation and secretion of submandibular and sublingual saliva
  • Efferent limb of the corneal reflex

Clinical significance

Bell palsy (LMN)

Acute, idiopathic, unilateral LMN facial palsy, probably caused by viral (HSV-1) inflammation and swelling in the narrow labyrinthine segment. It produces weakness of the entire half of the face, including the forehead:
• inability to close the eye, with a risk of exposure keratitis;
• a drooping mouth and flattened nasolabial fold;
• often loss of taste, hyperacusis and post-auricular pain.

Treatment is prednisolone within 72 hours plus eye protection. About 70–85% of patients recover completely. Bilateral facial palsy suggests Lyme disease, sarcoidosis or Guillain–Barré syndrome.

UMN facial weakness (forehead sparing)

The part of the facial motor nucleus that supplies the upper face receives bilateral corticobulbar input, whereas the lower face receives mainly contralateral input. A unilateral UMN lesion, such as a stroke in the motor cortex or internal capsule, therefore causes contralateral lower facial weakness with the forehead spared. Emotional (involuntary) smiling may also be preserved.

Ramsay Hunt syndrome and parotid lesions

Ramsay Hunt syndrome is reactivation of varicella-zoster virus in the geniculate ganglion. It causes an LMN facial palsy with painful vesicles in the ear canal and auricle, often with vertigo and hearing loss, and has a worse prognosis than Bell palsy. Parotid malignancy or surgery can injure the terminal branches. Facial palsy in a parotid mass strongly suggests malignancy; benign pleomorphic adenomas rarely cause palsy.

Mnemonics

Terminal branches

"To Zanzibar By Motor Car": Temporal, Zygomatic, Buccal, Marginal mandibular, Cervical.

Facial nerve functions

"Face, ear, taste, tear": muscles of face, stapedius in the ear, taste from the anterior 2/3 of the tongue, and tear (lacrimal) plus salivary secretion.

Compiled from standard anatomy and physiology references — see the Nervous System sources. For education only; not medical advice.