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Myelin surrounding a nerve axon, coloured transmission electron micrograph (TEM). The concentric round rings are the sheets of a Schwann cell's myelin membrane (blue rings) tightly wound around the axon (centre). Schwann cells wrap themselves around nerve axons of the peripheral nervous system, creating a myelin sheath (myelination). Myelination helps to both electrically insulate the nerve from surrounding tissue and propagate (speed up) electrical impulses along the axon. Not much of the actual Schwann cell can be seen as the myelin profile takes up most of the image. Magnification: x25,000 when printed 10 centimetres wide.
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