Inner ear hair cells. Coloured scanning electron micrograph (SEM) of sensory inner hair cells (stereocilia) from the organ of corti, in the cochlea of the inner ear. These cells are surrounded by a fluid called the endolymph. As sound enters the ear it causes waves to form in the endolymph, which in turn cause these hairs to move. The movement is converted into an electrical signal, which is passed to the brain. Each group of hairs lies on the top of a single cell. The dividing line between two of these cells is seen running vertically down from centre. Magnification: x12,000 when printed 10cm wide.