Facial nerve (VII)

At a glance

English

Facial nerve (VII)

Latin (TA2)

Nervus facialis (VII)

System

Nerve

Region

Head

Side

Paired, left and right

About the facial nerve (vii)

Cranial nerve VII, the facial nerve, is above all the motor nerve of facial expression, but it is mixed. Alongside its large motor root it carries a smaller root, the intermediate nerve (nervus intermedius), that holds its taste, parasympathetic and few skin-sensory fibres; together the two are sometimes called the intermediofacial nerve. Both leave the brainstem at the lower border of the pons, in the cerebellopontine angle, between the abducens nerve medially and the vestibulocochlear nerve laterally.

Its course is described in segments. After crossing the posterior cranial fossa it enters the internal acoustic meatus with the eighth nerve, then the facial canal of the petrous temporal bone. The short labyrinthine segment ends at a sharp bend, the genu, where the geniculate ganglion lies and the greater petrosal nerve leaves; that nerve passes through the pterygoid canal to the pterygopalatine ganglion, whose fibres drive the lacrimal gland and the glands of the nose and palate. The tympanic segment runs back along the medial wall of the middle ear above the oval window, close to the lateral semicircular canal; at the pyramidal eminence the nerve turns down as the mastoid segment, giving the nerve to stapedius and the chorda tympani. The chorda brings taste from the tongue's front two-thirds and secretory fibres for the submandibular and sublingual glands.

The nerve leaves the skull through the stylomastoid foramen. It at once gives the posterior auricular nerve to the muscles around the ear and twigs to stylohyoid and to the back belly of digastric. It then enters the parotid gland, which it passes through without supplying, and divides into the parotid plexus, from which five groups of branches fan out over the face; from above down they are the temporal, zygomatic and buccal branches, the marginal branch along the jaw, and the cervical branch.

Weakness of the face is the key sign of damage. A lesion of the nerve itself, as in Bell's palsy, which is thought to follow viral inflammation, weakens the whole of one side: the brow cannot wrinkle, the eye cannot close firmly and the mouth droops. A stroke above the nucleus spares the forehead, because the upper face receives input from both hemispheres. The nerve is also the outgoing limb of the blink (corneal) reflex.

Course and supply

Arises from

The facial motor nucleus in the pons (motor root) and, through the intermediate nerve, the superior salivatory nucleus, solitary nucleus and geniculate ganglion; it leaves the brainstem at the cerebellopontine angle.

Ends in

Ends in the parotid plexus, whose branches spread to the temple, cheekbone, cheek, jaw margin and neck, after giving the greater petrosal nerve, nerve to stapedius, chorda tympani and posterior auricular nerve.

Supplies

Motor to the muscles of facial expression, stapedius, stylohyoid and the hind belly of digastric; taste from the front two-thirds of the tongue; parasympathetic to the lacrimal, nasal, palatine, submandibular and sublingual glands; skin sensation from part of the outer ear.

Blood supply

Within the temporal bone it is supplied by the petrosal branch of the middle meningeal artery and the stylomastoid branch of the posterior auricular artery; the labyrinthine segment is the thinnest-supplied part.