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An otolith, (oto-, ear + lithos, a stone) or otoconium is a structure in the saccule or utricle of the inner ear. It is comprised of a combination of a gelatinous matrix and calcium carbonate crystals. Otolith crystals are relatively dense and heavy - they are connected to the rest of the body by the sensory processes of the macular cells. In fish, otoliths can be used for age determination, showing rings of different growth summer/winter, like tree rings.
Details
The otolith organs (the utricle and the saccule) are structures in the inner ear, specifically in the semicircular canals, that are sensitive to gravity and linear acceleration. Because of their orientation in the head, the utricle is sensitive to a change in horizontal movement, and the saccule gives information about vertical acceleration (such as when in an elevator).
Otoliths are small particles of calcium carbonate in the viscous fluid of the saccule and utricle. The inertia of these small particles causes them to stimulate hair cells when the head moves. The hair cells send signals down sensory nerve fibres, which are interpreted by the brain as motion.
In 1991, Martin Lenhardt of the University of Virginia discovered that the saccule has an additional function. As published in Science, Vol. 253, 5, 1991, 82, Lenhardt demonstrated that the saccule is also a hearing organ for ultrasonic sound.
The otolith is made up of a gelatinous matrix and statoconia.
When your head is in a normal upright position, the otolith presses on the sensory hair cell receptors in the ear. This pushes the hair cell processes down and prevents them from moving side to side. However, when the head is tilted, the pull of gravity on statoconia shift the hair cell processes to the side, distorting them and sending a message to the CNS (Central nervous system) that your head is no longer level but now tilted.
"Otolith"