Myelin is an electrically insulating phospholipid (fatty) layer that surrounds nerves cells and allows for faster and complete nerve conduction of messages.

Demyelination is the loss of the myelin sheath insulating the nerves, resulting in impairmant of nerve function  The hallmark of demyelnation is neurodegenerative autoimmune diseases in which the immune system may play an important role.

Heavy metal poisoning from mercury and other toxicities have been implicated as a major casue of demyelination.  It is written in medical literature that demyelnated fibers of the mammalian central nervous system do not regenerate, but contradicting evidence exists.