Nerve. Coloured scanning electron micrograph (SEM) of a freeze-fracture through a peripheral nerve. Schwann cells wraps their cell membrane around the nerve a number of times. In-between each cell membrane layer is a layer of myelin (pink), an electrically insulating fatty layer. A Schwann cell effectively thickens a nerve's membrane and increases the speed at which nerve impulses are relayed. The myelin surrounds the axons (cream). Endoneurial connective tissue (yellow) envelopes the nerve fibers. Magnification: x150 when printed at 10 centimetres wide.