Human hair. Coloured Scanning Electron Micrograph (SEM) of a shaft of human hair, with residue on its surface. Residue is coloured blue. The hair shaft has an outer cuticle of flat overlapping 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: x600 at 6x6cm size. x1000 at 4x5"~SQUARE"