Overview

First-order neurons have cell bodies in the vestibular (Scarpa) ganglion in the internal acoustic meatus; their peripheral processes innervate the maculae and cristae, and their central processes enter the brainstem with the cochlear nerve. Most end in the four vestibular nuclei (superior, lateral [Deiters], medial and inferior) in the floor of the fourth ventricle; some pass directly to the flocculonodular lobe of the cerebellum (the only primary sensory afferents to reach the cerebellar cortex directly).

Vestibulo-ocular reflex (VOR): stabilises images on the retina during head movement by rotating the eyes equally and opposite to the head, with a latency of <10 ms — far faster than visual tracking. For a head turn to the left: left lateral canal excited → left medial vestibular nucleus → crosses to the right abducens nucleus → right lateral rectus, and via the medial longitudinal fasciculus (MLF) to the left oculomotor nucleus → left medial rectus: both eyes move right. This three-neuron arc (vestibular ganglion → vestibular nucleus → ocular motor nucleus) is one of the simplest reflexes in the CNS. Sustained rotation produces nystagmus: a slow vestibular phase followed by a fast corrective saccade (named by the fast phase).

Vestibulospinal tracts: the lateral vestibulospinal tract (from Deiters nucleus, ipsilateral, whole cord) excites antigravity extensors; the medial vestibulospinal tract (bilateral, cervical) mediates the vestibulocollic reflex for head stability. Ascending projections via the thalamus (ventral posterior nuclei) reach a multisensory vestibular cortex in the parieto-insular region, contributing to the conscious sense of orientation. Connections with the reticular formation and area postrema underlie motion sickness (sensory conflict) and vomiting.

Location: Vestibular ganglion (internal acoustic meatus) → vestibular nuclei (pontomedullary floor of the fourth ventricle) → MLF, spinal cord, cerebellum, thalamus and cortex.

Parts & subdivisions

Vestibular ganglion and nerve
Superior and inferior divisions of the vestibular nerve.
Vestibular nuclei
Superior, lateral (Deiters), medial and inferior — integrate vestibular, visual, proprioceptive and cerebellar input.
Medial longitudinal fasciculus
Links vestibular, abducens, trochlear and oculomotor nuclei for conjugate eye movements; lesion → internuclear ophthalmoplegia.
Vestibulospinal tracts
Lateral (extensor tone, ipsilateral) and medial (neck muscles, head stabilisation).
Flocculonodular lobe (vestibulocerebellum)
Calibrates the VOR and controls balance; lesions → truncal ataxia and nystagmus.

Function

Stabilise gaze during head movement (VOR)
Maintain posture and balance (vestibulospinal reflexes)
Coordinate head–neck–eye movements and spatial orientation

Clinical significance

Doll's-eye (oculocephalic) reflex

In a comatose patient with an intact brainstem, turning the head causes the eyes to move in the opposite direction (VOR). Absence indicates brainstem dysfunction.

Peripheral vs central vertigo

Peripheral (labyrinth/nerve): unidirectional horizontal–torsional nystagmus suppressed by fixation, positive head-impulse test, often hearing symptoms. Central (brainstem/cerebellum): direction-changing or purely vertical nystagmus, normal head impulse, skew deviation, other neurological signs, inability to walk unaided — "HINTS" exam to detect stroke.

Motion sickness

Conflict between vestibular and visual signals (reading in a car, ships) produces nausea, pallor and vomiting; antihistamines (cyclizine) and antimuscarinics (hyoscine) help.

Mnemonics

Nystagmus naming

Nystagmus is named after its fast phase; in peripheral lesions it beats away from the hypofunctioning (damaged) side.

Test yourself

Brief vertigo on rolling over in bed, with torsional up-beating nystagmus after a few seconds' latency on the Dix–Hallpike test, is most likely due to:

Ménière disease
Vestibular neuritis
Benign paroxysmal positional vertigo of the posterior canal
Vestibular schwannoma

Answer: Benign paroxysmal positional vertigo of the posterior canal

Otoconia displaced from the utricle into the posterior semicircular canal (canalithiasis) cause BPPV — brief positional vertigo with latent, fatiguing torsional up-beating nystagmus. It is treated with the Epley manoeuvre.

Ice-cold water irrigated into the right ear of a conscious patient produces nystagmus whose fast phase beats:

To the left
To the right
Upwards
Downwards

Answer: To the left

COWS — Cold Opposite, Warm Same. Cold water inhibits the right lateral canal, producing a slow drift to the right and a corrective fast phase to the left.