otolit

Otoliths are tiny, calcareous structures found in the inner ear of all vertebrate animals, including humans. They are also commonly referred to as ear stones or statoconia. These structures are composed primarily of calcium carbonate in the form of aragonite crystals, embedded within an organic matrix. Otoliths are located within the sacculus and utricle, two of the three fluid-filled sacs of the vestibular system, which is responsible for sensing balance and spatial orientation.

The primary function of otoliths is to detect linear acceleration and gravity. They are denser than the surrounding fluid in the inner ear. When the head moves, inertia causes the otoliths to shift their position relative to the sensory hair cells of the maculae, specialized sensory areas within the sacculus and utricle. This movement bends the cilia of the hair cells, generating nerve impulses that are transmitted to the brain. These signals provide information about the head's position relative to gravity and its linear movements, such as forward or backward motion, and changes in speed. This information is crucial for maintaining balance, posture, and coordinating eye movements with head movements. In fish, otoliths are also important for hearing, as they transmit sound vibrations. The size, shape, and arrangement of otoliths vary significantly between different species, and their study can provide insights into the evolutionary history and ecology of fish.