Which structures constitute the peripheral vestibular apparatus and what are their sensory roles?

• A. Semicircular canals detect angular acceleration; otolith organs detect linear acceleration and gravity.
• B. Utricle and saccule detect angular acceleration; semicircular canals detect gravity.
• C. Cochlea detects sound; otoliths detect linear acceleration.
• D. Semicircular canals detect gravity; otolith organs detect angular velocity.

Answer: (A)

The peripheral vestibular apparatus is made up of two functional parts: semicircular canals and otolith organs. The semicircular canals sense rotational head movements, i.e., angular acceleration. Inside each canal is a crista ampullaris, a sensory epithelium that detects the flow of endolymph when the head rotates. That flow bends hair cells, signaling changes in angular velocity as the head turns.

The otolith organs—the utricle and the saccule—detect linear acceleration and gravity. They contain maculae with otoconia (calcium carbonate crystals) that shift under linear motion or changes in head position relative to gravity, deflecting hair cells and signaling linear movement and tilt.

Cochlea is for hearing, not part of the vestibular apparatus, and gravity is sensed via the otolith organs rather than the semicircular canals. The described roles match the correct understanding of how these peripheral vestibular structures work.