Myelin is a substance that forms an insulating sheath around the axons of nerve cells in the central and peripheral nervous systems. Myelin is mainly made up of lipids and in the central nervous system is formed from the oligodendrocytes, a form of neuroglia that serve to protect and insulate axons. In the peripheral nerve system, myelin is formed from Schwann cells.
Any disorder that leads to the destruction of this myelin covering is referred to as demyelinating disease. Damage to the myelin sheath disrupts nerve signal conduction, resulting in neurological symptoms such as reductions in sensation, cognitive ability and movement as well as decreases in any other functions that depend on nerve signalling.
The mechanisms underlying demyelination are not clearly understood but contributory factors thought to be involved include:
The symptoms of demyelination depend on the type of demyelinating disease a person has and whether the central nervous system or peripheral nervous system is affected. Examples of some of the symptoms that may manifest in demyelinating diseases include: