Myelin is a dielectric (electrically insulating) material that forms a layer, the myelin sheath, usually around only the axon of a neuron. It is essential for the proper functioning of the nervous system.
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Demyelination
Further information: Demyelinating disease
Demyelination is the loss of the myelin sheath insulating the nerves, and is the hallmark of some neurodegenerative autoimmune diseases, including multiple sclerosis, acute disseminated encephalomyelitis, Neuromyelitis Optica, transverse myelitis, chronic inflammatory demyelinating polyneuropathy, Guillain-Barré syndrome, central pontine myelinosis, inherited demyelinating diseases such as leukodystrophy, and Charcot-Marie-Tooth disease. Sufferers of pernicious anaemia can also suffer nerve damage if the condition is not diagnosed quickly. Subacute combined degeneration of spinal cord secondary to pernicious anaemia can lead to slight peripheral nerve damage to severe damage to the central nervous system, affecting speech, balance, and cognitive awareness. When myelin degrades, conduction of signals along the nerve can be impaired or lost, and the nerve eventually withers.[clarification needed] A more serious case of myelin deterioration is called Canavan Disease.
The immune system may play a role in demyelination associated with such diseases, including inflammation causing demyelination by overproduction of cytokines via upregulation of tumor necrosis factor[7] or interferon.
Symptoms
Demyelination results in diverse symptoms determined by the functions of the affected neurons. It disrupts signals between the brain and other parts of the body; symptoms differ from patient to patient, and have different presentations upon clinical observation and in laboratory studies.
Typical symptoms include:
blurriness in the central visual field that affects only one eye, may be accompanied by pain upon eye movement
double vision
loss of vision/hearing
odd sensation in legs, arms, chest, or face, such as tingling or numbness (neuropathy)
weakness of arms or legs
cognitive disruption, including speech impairment and memory loss
heat sensitivity (symptoms worsen or reappear upon exposure to heat, such as a hot shower)
loss of dexterity
difficulty coordinating movement or balance disorder
difficulty controlling bowel movements or urination
fatigue
Myelin repair
Research to repair damaged myelin sheaths is ongoing. Techniques include surgically implanting oligodendrocyte precursor cells in the central nervous system and inducing myelin repair with certain antibodies. While results in mice have been encouraging (via stem cell transplantation), whether this technique can be effective in replacing myelin loss in humans is still unknown.[8] Cholinergic treatments, such as acetylcholinesterase inhibitors (AChEIs), may have beneficial effects on myelination, myelin repair, and myelin integrity. Increasing cholinergic stimulation also may act through subtle trophic effects on brain developmental processes and particularly on oligodendrocytes and the lifelong myelination process they support. By increasing oligodendrocyte cholinergic stimulation, AChEIs, and other cholinergic treatments, such as nicotine, possibly could promote myelination during development and myelin repair in older age.[9] Glycogen synthase kinase 3β inhibitors such as lithium chloride have been found to promote myelination in mice with damaged facial nerves. Cholesterol is a necessary nutrient for the myelin sheath.[10]
