Sliced open with a diamond-edged knife, a nerve cell looks a bit like a tunnel. The sciatic nerve (lower right corner) carries electrical signals from the spinal cord down the leg – but not without some help. As the nerve develops, its body (known as an axon) is surrounded by Schwann cells – they treat axons a bit like sticks in a candy floss machine, wrapping them in layer upon layer of waxy myelin (black rings). Over 30 myelin rings can be counted around this nerve thanks to the detail of transmission electron microscopy. A myelin ‘sheath’ not only protects the sciatic nerve, but fine-tunes its electrical properties, shaping the sensations we feel in our lower limbs. Researchers have recently managed to grow stocks of fresh Schwann cells from stem cells found in human skin, an important step towards replacing myelin in patients with nerve injuries.
Written by John Ankers
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