Which structures in the inner ear are responsible for sensing rotational movement in three planes?

• A. They are located in the hearing cochlea
• B. They detect linear acceleration
• C. They are arranged in perpendicular planes
• D. They sense sound vibrations

Answer: (C)

The semicircular canals in the inner ear detect rotational movement in three planes. They are arranged in perpendicular (orthogonal) planes so that head rotation around any of the three axes—like nodding, shaking, or tilting—creates fluid movement in a corresponding canal. Inside each canal, hair cells in the ampulla bend as endolymph lags behind the motion, sending signals to the brain about angular velocity. This setup lets you sense rotation in all directions.

Rotation isn’t sensed by the hearing cochlea, nor by structures that detect linear acceleration (the otolith organs) or by those that sense sound vibrations.