Semicircular canals detect angular acceleration

The semicircular canals consist of three torus-shaped pipes, filled with liquid, arranged almost perpendicular to each other like the x, y, and z axes in geometry. They detect the rotational movements of our heads, known as angular accelerations.

When our head moves, the liquid within these closed-end pipes initially maintains its inertia. The resulting relative movement discrepancy causes the sail-shaped receptors(cupula) to tilt in the opposite direction of the movement. The hair cells within the ampulla detect the movement of the cupula, akin to a compass needle always remaining stationary. However, this initial inactivity is short-lived, and if the rotation persists, the liquid begins to rotate with the bony tube around it. When we abruptly stop moving, the fluid within the stationary bone continues to rotate, resulting in the sensation of our head continuing to spin momentarily.

It is worth noting that since there are two sets of semicircular canals on both sides of our head, they work in pairs, and the information they transmit is combined and processed in the brain. This increases the precision of the data and gives redundancy.