Transmission electron micrograph (TEM) of pillar cells of the mammalian organ of Corti. In the organ of Corti in the inner ear, the hair cells responsible for transduction of mechanical vibration to a nerve impulse are supported by rows of cells called pillar cells. The micrograph shown here illustrates the thick-walled microtubules in a pillar cell. These highly ordered stable arrays of microtubules, interrupted by occasional mitochondria and tubular elements of the endoplasmic reticulum, are believed to exemplify a purely mechanical cytoskeletal function of microtubules.