Each semicircular duct widens at one end into an ampulla that opens into the utricle. Inside each ampulla is a ridge, the crista ampullaris, carrying hair cells whose stereocilia project into a gelatinous dome called the cupula. The cupula spans the ampulla like a swinging door.
| Location | Ends of the anterior, posterior and lateral semicircular ducts near the utricle |
|---|---|
| Parts |
|
| Nerve Supply | Ampullary nerves of the superior and inferior vestibular nerves (CN VIII) |
| Blood Supply | Anterior and posterior vestibular arteries |
House the receptors that sense rotational acceleration of the head.
When the head rotates, endolymph lags behind and pushes the cupula, bending the hair cells and changing nerve firing. The caloric test warms or cools the ear canal to set up convection currents in the lateral duct and stimulate its crista. Alcohol can change the density of the cupula relative to endolymph, causing positional vertigo when drunk.
Reduced response of one lateral crista on caloric testing, indicating unilateral peripheral vestibular weakness.
Alcohol diffuses unevenly into the cupula and endolymph, making the cupula sensitive to gravity and causing positional vertigo.
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