Inner ear balance sensing. Coloured scanning electron micrograph (SEM) of bundles of cilia (hair cells, yellow) and otoliths (round, red) in the human inner ear. The cilia and otoliths detect directional movement, such as the tilting of the head. They are immersed in a fluid, called the endolymph. Currents in this fluid displace the position of the cilia and otoliths, triggering nerve impulses that are sent to the brain through the vestibular nerve.