Expansion
Semicircular canals sense rotation; otolith organs sense linear acceleration and gravity
Expansion
Semicircular canals (anterior, posterior, horizontal): sense angular acceleration. Endolymph lags behind head movement, deflecting the cupula and hair cells within the ampulla. The three canals lie at right angles, and each is paired with its opposite counterpart on the other side, working in a push-pull fashion.
Otolith organs: sense linear acceleration and head tilt, using calcium carbonate otoconia resting on a gelatinous membrane
- Utricle: horizontal plane
- Saccule: vertical plane
Vestibulo-ocular reflex: head rotation produces an equal and opposite eye movement, stabilising gaze. It is tested by the head impulse test and by caloric testing.
Clinical correlates:
- Benign paroxysmal positional vertigo: otoconia displaced into a semicircular canal, usually the posterior, giving brief vertigo on position change with a characteristic latency and fatigability. Treated by repositioning manoeuvres
- Vestibular neuronitis: sudden unilateral loss, with an abnormal head impulse test
- Central causes are suggested by a normal head impulse test with direction-changing nystagmus and skew deviation