Vestibule of the inner ear

Vestibulum auris internae

Also known as: vestibule, otolith organs, vestibular apparatus

The central oval chamber of the bony labyrinth (≈4–5 mm), between the cochlea and semicircular canals; it contains the utricle and saccule (otolith organs), which sense gravity and linear acceleration.

Overview

Size≈4–5 mm

Openings of semicircular canals5 (common crus shared)

The bony vestibule communicates anteriorly with the scala vestibuli of the cochlea and posteriorly with the semicircular canals through five openings (the anterior and posterior canals share a common crus). Its lateral wall contains the oval window (occupied by the stapes footplate); its medial wall faces the fundus of the internal acoustic meatus and has two depressions — the spherical recess (for the saccule) and the elliptical recess (for the utricle) — perforated by vestibular nerve filaments (maculae cribrosae). The vestibular aqueduct, carrying the endolymphatic duct, opens on the medial wall.

Within it, suspended in perilymph, lie the two otolith organs of the membranous labyrinth: the larger utricle and the smaller saccule. Each contains a sensory macula of hair cells covered by an otolithic membrane loaded with calcium carbonate crystals (otoconia). Because otoconia are denser than endolymph (≈2.7×), gravity and linear acceleration shift the membrane relative to the hair cells, deflecting their bundles. Each macula contains hair cells oriented in all directions, with polarity reversing across a curved line, the striola, so every direction of tilt or linear acceleration excites a specific population.

The utricular macula lies roughly horizontal (sensing horizontal acceleration and head tilt), and the saccular macula roughly vertical (sensing vertical acceleration, e.g. lifts and jumping). Together with the semicircular canals they form the vestibular apparatus, sending information via the vestibular nerve to the vestibular nuclei and cerebellum.

Location

Central part of the bony labyrinth, medial to the middle ear (oval window), between the cochlea (anterior) and semicircular canals (posterior).

Parts & subdivisions

Utricle

Larger otolith organ with a horizontal macula; receives the five openings of the semicircular ducts.

Saccule

Smaller otolith organ with a vertical macula; connected to the cochlear duct.

Otoconia

Calcium carbonate (calcite) crystals ≈1–30 µm embedded in the otolithic membrane.

Striola

Line of hair-cell polarity reversal in each macula.

Oval window

In the lateral wall; closed by the stapes footplate.

Anatomy

Innervation

Superior vestibular nerve — utricular macula and part of the saccular macula (plus anterior and lateral cristae); inferior vestibular nerve — most of the saccular macula (plus posterior crista). Cell bodies in the vestibular (Scarpa) ganglion in the internal acoustic meatus.

Arterial supply

Anterior vestibular artery (from the labyrinthine artery) and the vestibular branch of the common cochlear artery.

Clinical significance

Vestibular neuritis

Viral inflammation of the (usually superior) vestibular nerve: sudden, severe, continuous vertigo lasting days, nausea, horizontal–torsional nystagmus beating away from the affected side and an abnormal head-impulse test, without hearing loss. Must be distinguished from posterior circulation stroke (HINTS examination).

Vestibular evoked myogenic potentials (VEMPs)

Loud clicks stimulate the saccule, producing a reflex inhibition of the ipsilateral sternocleidomastoid (cervical VEMP); used to test saccular/inferior vestibular nerve function and to diagnose superior canal dehiscence.