Degenerating nerve. Coloured transmission electron micrograph (TEM) of a section through a Schwann cell that has lost it's axon and contains large amounts of myelin debris (brown) from the degenerated nerve sheath. A nerve's myelin sheath helps it conduct electrical impulses and when the myelin sheath is lost, nerve function is impaired. This is seen in nerve disorders such as multiple sclerosis (MS), where patches (lesions) of myelin sheath are destroyed. Magnification: x 3000 when printed at 10 centimetres wide.