Otoliths, or otoconia, are tiny calcium carbonate crystals embedded in the gelatinous otolithic membrane that lies over the maculae of the utricle and saccule. Because they are denser than endolymph, they lag behind or slide with gravity when the head tilts or accelerates. This drag bends the hair cell bundles beneath them.
| Location | On the otolithic membranes of the maculae of the utricle and saccule |
|---|---|
| Parts |
|
| Nerve Supply | Vestibular nerve fibres serving the underlying hair cells (CN VIII) |
| Blood Supply | None (acellular) |
Give the otolith organs mass so they respond to gravity and linear acceleration.
Otoconia can break loose with age, head injury or inner ear disease and drift into a semicircular duct, most often the posterior one. There they move with gravity and falsely signal rotation, causing benign paroxysmal positional vertigo. The Dix-Hallpike test diagnoses posterior canal BPPV.
Free-floating otoconia in the posterior semicircular duct cause brief vertigo when lying down, rolling over or looking up, with characteristic rotatory nystagmus.
Otoconia stuck to the cupula of a semicircular duct, causing more persistent positional vertigo.
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