Myelin is the material that surrounds the axons of the nerve cells and acts as insulation like rubber or plastic insulation on wires. Nerve axons are like little wires that conduct electrical impulses. There are two types of myelin. Central myelin is in the brain and spinal cord and is made of oligodenrocytes wrapping around the axon. Peripheral myelin is made by Schwann cells wrapping around the axons of peripheral nerves. Peripheral nerves are outside the brain and spinal cord. Demyelinating disease is one where the myelin is damaged, so the nerves can't conduct impulses properly. An example of a central demyelinating disease is MS. An example of a peripheral demyelinating disease is Guillan-Barre syndrome. I hope that this was helpful.
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