A multiple sclerosis patient develops blurred vision and limb weakness that comes and goes. MS destroys myelin — the insulating sheath made by oligodendrocytes in the CNS — so nerve signals slow or scatter. The optic nerve (vision) and spinal tracts (limb strength) are common targets; symptoms flare during attacks and partly remit. This is why MS is a CNS demyelinating disease, distinct from peripheral nerve injuries.