The otoliths consist of two organs in the inner ear: saccule and utricle. Both consist of stones (small calcium carbonate particles in a gelatinous membrane) resting on hairs (stereocilia). Motions of the head result in the stones exerting a shearing force on the hairs, which is detected by the hair cells. The impulse is sent to the brain via branches of the vestibular nerve, with that from the saccule traveling via the inferior division and the utricle via the superior division of the nerve. Both organs sense gravity and linear acceleration. However, given their orientation in the head, the utricle (in the axial plane) is sensitive to horizontal accelerations and the saccule (in the coronal plane) to vertical motion. Both organs are formed during early embryogenesis with their formation being completed in the early postembryonic period. Prenatal stimulation of the otoliths during the third trimester has been linked to hand preference and auditory lateralization in postnatal life according to the left-otolithic dominance hypothesis. The specific effects of this stimulation are posited to be dependent on head position in utero (delivery position) during the last trimester.
See Conditional knockouts, Cranial nerves, Delivery position (or presentation), Hand preference, Vestibular labyrinths, Vestibular system