Myelinated nerves. Coloured scanning electron micrograph (SEM) of a freeze-fracture through peripheral nerves to show myelinated nerves. A Schwann cell wraps its cell membrane around the nerve a number of times. In-between each cell membrane layer is a layer of myelin (brown), 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 (yellow). Endoneurial connective tissue (pink) envelopes the nerve fibers. Magnification: x1000 when printed at 10 centimetres wide.