Peripheral nerves. Coloured scanning electron micrograph (SEM) of a freeze-fracture through peripheral nerves to show Schwann cells (yellow) and myelinated nerve fibres (pink). A Schwann cell wraps its cell membrane around a nerve (axon) a number of times. In between each layer of membrane is a layer of myelin, an electrically insulating fatty layer. A Schwann cell effectively thickens a nerve's membrane and increases the speed at which nerve impulses are relayed. Endoneurium, delicate connective tissue (beige) surrounds the myelinated nerve fibres. Magnification not known.