Otolith Organs

The utricle and saccule, sensors of gravity and linear motion

Overview

The otolith organs, the utricle and saccule, are the parts of the vestibular system that detect linear acceleration and the pull of gravity. Each contains a sensory patch called a macula, in which hair cells are covered by a gelatinous membrane studded with otoconia, tiny crystals of calcium carbonate. Because the crystals are denser than the surrounding fluid, tilting the head or accelerating shifts the membrane and bends the hair cells. The utricle is mainly oriented for horizontal motion and the saccule for vertical motion. Dislodged otoconia are the cause of benign paroxysmal positional vertigo.