Human hair. Coloured Scanning Electron Micrograph (SEM) of the surface of a shaft of human hair. The hair shaft has an outer cuticle of flat over- lapping scales or plates, as seen here, which it is thought, prevent the hairs from matting together. Hair is made up of a fibrous protein called keratin. Internally the hair shaft is divided into three concentric sheaths (layers) called the medulla, cortex and outer cuticle. It consists of non-living tissue. Hair growth occurs when epidermal cells divide within the root bulb. Magnification: x660 at 6x6cm size. x1000 at 4x5"~SQUARE"