As part of the nervous system, myelin lines nerve fibers to protect and insulate neurons. Myelin aids in the quick and accurate transmission of electrical current carrying data from one nerve cell to the next. When myelin becomes damaged, the process involves numerous health conditions, including multiple sclerosis.
Nerves are like an electrical wire. Current (the message) must be conducted along a path (the nerve) to successfully get from point A to point B (the brain to a fingertip). The electrical current must travel without being corrupted, scrambled, diverted from the proper path, or leaking energy. Therefore, myelin is like the layer of plastic insulation surrounding an interior wire, which is the nerve. Additionally, myelin speeds the conduction, so it's also analogous to a secondary coating on the wire that reduces the resistance facing an electrical current. The interior wire represents the series of axons and nerve cells that relay the electrical impulse.
Myelin is always made of lipids of proteins, but it functions slightly differently depending on where in our nervous system it's employed. Our body has a Peripheral Nervous System, PNS, that branches from the spinal cord to carry information related to sensory input, while our brain's Central Nervous System, CNS, determines how to act on that input. Each of these systems synthesizes myelin in a different way, so different complications can result.
Dysfunction in the myelin of nerve fibers causes the interruption of smooth delivery of information. Either nerve impulses can be slowed, such that we can't pull our hand away in time to avoid being burned, or mixed up, so we aren't able to determine if a pan is hot in the first place. This is akin to a pet chewing on a wire, causing the device to dysfunction. When problems arise in nerves of the PNS, neuropathy might result, and when injury affects the nerves of the CNS, multiple sclerosis is often diagnosed.
This serious disease, multiple sclerosis, causes demyelination. In demyelination, an auto-immune reaction, our body attacks our own healthy myelin, deteriorating and scarring the important lining. In later stages, the cells that produce myelin in the CNS, oligodendrocytes, are destroyed so that no further replacement is possible. This permanently weakens and damages the entire nerve, resulting in compromised axons in extreme cases. Researchers are looking into preventing this auto-immune response, as well as stimulating oligodendrocytes to replace the damaged myelin before they are themselves attacked.