Facial nerve (CN VII)
Nerve · CN VII Mixed
The motor root from the facial nucleus and the nervus intermedius (taste and parasympathetic) leave the pons at the cerebellopontine angle, enter the internal acoustic meatus with VIII, and run through the facial canal in the petrous temporal bone, where the greater petrosal nerve leaves at the geniculate ganglion, then the nerve to stapedius, then the chorda tympani. The nerve exits at the stylomastoid foramen and branches within the parotid gland.
Traced from the start
- Pons
- Facial nerve (CN VII)
Detail
- Motor
- Muscles of facial expression, stapedius, posterior belly of digastric, stylohyoid, occipitalis and auricular muscles
- Parasympathetic
- Greater petrosal → pterygopalatine ganglion → lacrimal, nasal and palatine glands; chorda tympani → submandibular ganglion → submandibular and sublingual glands
- Sensory
- Taste from the anterior two-thirds of the tongue and soft palate (chorda tympani, greater petrosal); a small patch of skin of the concha and external auditory meatus
- Upper vs lower motor neurone
- The forehead (frontalis, upper orbicularis oculi) receives bilateral cortical input, so a cortical or capsular lesion spares the forehead; a nuclear or nerve lesion weakens the whole hemiface
When it goes wrong
Bell's palsy: acute idiopathic lower motor neurone palsy, probably herpes simplex reactivation with oedema of the nerve inside the narrow facial canal
Sudden unilateral weakness of the whole hemiface including the forehead, incomplete eye closure with Bell's phenomenon, drooling, often hyperacusis (stapedius), loss of taste (chorda tympani) and post-auricular pain; prednisolone within 72 hours plus eye lubrication and taping, and most recover fully
Stroke or tumour above the facial nucleus (upper motor neurone lesion)
Contralateral weakness of the lower face with forehead sparing, usually with arm weakness or dysphasia from the same lesion
Ramsay Hunt syndrome: varicella zoster reactivation in the geniculate ganglion
Lower motor neurone facial palsy with painful vesicles in the external ear canal or on the palate, often with vertigo and deafness from VIII involvement; aciclovir with prednisolone, and recovery is poorer than Bell's palsy
Lesion proximal to the geniculate ganglion (cerebellopontine angle tumour, petrous fracture) versus at or beyond the stylomastoid foramen (parotid tumour or surgery)
Proximal: dry eye, loss of taste, hyperacusis and facial weakness together. Distal: facial weakness alone with lacrimation, taste and hearing intact
Practise this structure
2 questions in the bank tagged Facial Nerve.
A 52-year-old woman has had two months of numbness over the right forehead, the right upper eyelid and the tip of her nose, with a gritty feeling in the right e…
Foundations · middle twist
A 44-year-old man has had drooping of the right side of his face for three days. He drools from the right corner of his mouth, the right nasolabial fold is flat…
Foundations · common