<P> 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 or interferon . </P> <P> 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 . </P> <P> Typical symptoms include: </P> <Ul> <Li> blurriness in the central visual field that affects only one eye, may be accompanied by pain upon eye movement </Li> <Li> double vision </Li> <Li> loss of vision / hearing </Li> <Li> odd sensation in legs, arms, chest, or face, such as tingling or numbness (neuropathy) </Li> <Li> weakness of arms or legs </Li> <Li> cognitive disruption, including speech impairment and memory loss </Li> <Li> heat sensitivity (symptoms worsen or reappear upon exposure to heat, such as a hot shower) </Li> <Li> loss of dexterity </Li> <Li> difficulty coordinating movement or balance disorder </Li> <Li> difficulty controlling bowel movements or urination </Li> <Li> fatigue </Li> <Li> tinnitus </Li> </Ul>

What part of the neuron is covered in myelin sheath