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How do the semicircular canals detect head rotation?

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Compound eye — Senses Vespid wasps (Vespidae), similar to other insects, have compound eyes that consist of thousands of tiny optical units known as ommatidia, which contain light-sensitive photoreceptor cells.

The three semicircular canals—positioned at right angles to one another—function as rotary accelerometers to detect head rotation in three-dimensional space.12

When the head begins to rotate, the inertia of the endolymph fluid within the canals causes it to lag behind. This movement of fluid exerts pressure on the cupula, a gelatinous structure located in the ampulla at the base of each canal. As the cupula is deflected, it bends the stereocilia of the sensory hair cells embedded within it.132

This mechanical bending triggers the hair cells to send nerve impulses to the brain. The direction of the deflection determines the response: bending the stereocilia toward the kinocilium depolarizes the hair cells and increases the rate of nerve discharge, while bending them in the opposite direction hyperpolarizes the cells and decreases the discharge rate. Through these varying levels of excitation, the vestibular system accurately detects the direction and speed of head rotation.12