Normally, your immune system helps protect you. It does this by sending in white blood cells and special proteins whenever a foreign substance (like a bacterium or virus) invades your body.
Multiple sclerosis is an autoimmune disease, meaning your own immune system is damaging your body.
The immune system mistakenly believes the healthy tissues in your brain and spinal cord are foreign invaders. Immune cells are sent from the blood into the central nervous system, where they produce chemicals that cause inflammation.
Myelin is a fatty substance that insulates most nerves and helps speed up the communication between your brain and other parts of your body.
This inflammation causes the myelin around the nerves to break down, and scar tissue begins to form in its place. This process is called "demyelination."
The name "multiple sclerosis" simply refers to the multiple locations where scar tissue, or "sclerosis," builds up in the brain and spinal cord.
As the myelin sheath becomes damaged, the electric signals have a harder time getting through -- or become blocked entirely. As the damage progresses, this leads to problems with your muscle control, vision, speech, sensation, and even your thinking.
The symptoms of MS and how severe they are vary from person to person. This depends on how much myelin has been lost and what parts of the central nervous system are affected.