Picture of Nerve Fibers and Myelin Attack in MS
In multiple sclerosis, an agent such as a virus or foreign antigen, in theory, may alter or interact with the immune system so that the immune system perceives myelin as an intruder and attacks it. Inflammation occurs and causes myelin to disappear. Consequently, the electrical impulses that travel along the nerves decelerate, that is, become slower. In addition, the nerves themselves are damaged. While some of the myelin may be repaired after the assault, some of the nerves are stripped of their myelin covering (become demyelinated). Scarring also occurs, and material is deposited into the scars and forms plaques. As more and more nerves are affected, a person experiences a progressive interference with functions that are controlled by the nervous system such as vision, speech, walking, writing, and memory.
Image Source: MedicineNet
Text: MedicineNet: "Multiple Sclerosis."