Myelinated nerve fibre. Coloured scanning electron micrograph (SEM) of a section across a nerve fibre to reveal its structure. The central nerve cell axon (red) is the output process of a nerve cell. It is surrounded by an insulating fatty layer (myelin sheath, brown). Myelin isolates the nerve from its surroundings, increasing the speed of nerve transmissions. Nerves collect, interpret and relay information, passing it to other parts of the body, such as the muscles and organs like the brain.