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The semicircular canals
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Inside the inner ear there are three small curved tubes, the semicircular ducts, set at right angles to each other, like the three planes that meet in the corner of a room. Together they register the turns of the head, what physiology calls angular acceleration.
Each duct widens at one point into an ampulla, and inside it sits the crista ampullaris, which is the sensory tissue. It is covered by the cupula, a kind of gel that anchors the hair cells, the cells with tiny hairs that turn movement into a signal.
When you turn your head, the fluid inside, the endolymph, accelerates and pushes on those tiny hairs, the stereocilia: depending on which way you turn, it pushes them toward the kinocilium or away from it. When they bend toward the kinocilium, the cell depolarizes, which is its way of signaling.
There is a division of labor worth keeping straight. The crista ampullaris carries no otoliths, tiny crystals: straight-line acceleration and gravity are handled by the utricle and the saccule, not by these three ducts.
In brief
Set at right angles to one another, the three semicircular ducts detect angular acceleration and head rotation.
Three hoops set in the three planes of a corner.
Each duct widens into an ampulla containing the crista ampullaris, capped by the cupula, a gel that holds the hair cells.
When the head turns, endolymph pushes the stereocilia; when they bend toward the kinocilium, the cell depolarizes.
The crista ampullaris has no otoliths; the utricle and saccule sense linear acceleration and gravity.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingPhysiology, Vestibular System, StatPearlsPublished
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