Vestibular nerve

At a glance

English

Vestibular nerve

Latin (TA2)

Nervus vestibularis

System

Nerve

Region

Head

Side

Paired, left and right

About the vestibular nerve

Together with the cochlear nerve, the vestibular nerve makes up the eighth cranial (vestibulocochlear) nerve. It is made of bipolar sensory neurons whose cell bodies form the vestibular ganglion (of Scarpa), which lies at the lateral, deep end of the internal acoustic meatus. Their peripheral processes reach the hair cells of the inner ear's balance organs, and their central processes run medially with the cochlear nerve to enter the brainstem at the pontomedullary junction.

Distally the nerve divides as it passes through the perforated fundus of the meatus. A superior part goes through the upper vestibular area to the macula of the utricle and the ampullae of the anterior and lateral semicircular ducts. An inferior part crosses the lower vestibular area to the macula of the saccule. A posterior branch runs through a separate small canal, the foramen singulare, to the ampulla of the posterior duct. Some texts merge the last two and describe only two divisions. Centrally, most fibres end in the vestibular nuclei in the lateral floor of the fourth ventricle, spanning pons and medulla; some go straight to the cerebellum.

The otolith organs report gravity and straight-line acceleration of the head, while the canals report turning. Together they tell the brain where the head is and how it is moving, so that posture can be corrected and the eyes held steady on a target through the vestibulo-ocular reflex. The nerve's input also feeds into spatial memory, navigation and the reflex adjustment of blood pressure when the body changes position.

Damage, as in vestibular neuritis, Ménière's disease, inflammation or ototoxic antibiotics, causes sudden vertigo with nausea and vomiting, unsteadiness and horizontal nystagmus. Most people recover within days to weeks as the brain recalibrates, a process called vestibular compensation; balance exercises with a physiotherapist speed this up, and betahistine is sometimes given. A few never fully compensate and have recurrent attacks. A vestibular schwannoma, a benign tumour of the Schwann cells of this nerve within the meatus, usually presents with one-sided hearing loss and tinnitus.

Course and supply

Arises from

Bipolar neurons of the vestibular ganglion in the lateral part of the internal acoustic meatus.

Ends in

Peripherally the maculae of utricle and saccule and the ampullary crests of the three semicircular ducts; centrally the vestibular nuclei and the cerebellum.

Supplies

Sensory for balance: head position relative to gravity, linear acceleration and rotation, used for posture and gaze stability.