How do the semicircular canals detect rotation of the head?

The three semicircular canals—positioned at right angles to one another—detect rotational head movements through the movement of endolymph, a fluid contained within these structures.12

When the head begins to rotate, the inertia of the endolymph causes it to lag behind, exerting pressure that deflects the cupula, a jellylike mass located in the ampulla at the base of each canal. This deflection bends the stereocilia and kinocilia of the hair cells embedded within the cupula.1234

The direction of this bending determines the neural response:
* Depolarization: When stereocilia bend toward the kinocilium, ion channels open, allowing an influx of potassium ions that increases the rate of nerve impulses sent to the central nervous system.125
* Hyperpolarization: When stereocilia bend away from the kinocilium, ion channels close, decreasing the rate of discharge.125

This mechanism allows the vestibular system to perceive angular acceleration and maintain balance and visual stability during movement.123