Semicircular Canals

Three fluid filled loops that sense head rotation

Overview

Each inner ear has three semicircular canals, anterior, posterior, and horizontal, arranged roughly at right angles to one another so that together they can detect rotation in any direction. Each canal is filled with endolymph and has a swelling, the ampulla, containing a gelatinous cupula embedded with hair cells. When the head turns, the fluid lags behind and bends the cupula, signalling the direction and speed of rotation. The canals on the two sides work in matched pairs. Loose otoconia drifting into a canal cause BPPV, and a thinned bony wall causes superior canal dehiscence.