If you or a loved one has multiple sclerosis (MS), you already know about the symptoms. They may include muscle weakness, trouble with coordination and balance, vision problems, thinking and memory issues, and sensations such as numbness, prickling, or "pins and needles."
What you may not know is how this autoimmune disease actually affects the body. How does it interfere with the messaging system that helps your brain control your actions?
MS attacks tissues in the brain and spinal cord, known as the central nervous system (CNS). This system includes the complex network of nerve cells responsible for sending, receiving, and interpreting information from all parts of the body.
During daily life, the spinal cord sends information to the brain via these nerve cells. The brain then interprets the information and controls how you react to it. You can think of the brain as the central computer and the spinal cord as a cable between the brain and the rest of the body.
Nerve cells (neurons) carry messages from one part of the body to another through electrical and chemical impulses. Each has a cell body, dendrites, and an axon. The dendrites are thin, web-like structures that branch out from the cell body. They act like receptors, receiving signals from other nerve cells and transmitting them to the cell body.
The axon, also called a nerve fiber, is a tail-like projection that serves the opposite function as the dendrites: it sends electrical impulses out to other nerve cells.
A fatty material known as myelin covers the axon of the nerve cell. This covering protects and insulates the axon much like the rubber shell that protects and insulates an electric cord.
Myelin is made of up lipids (fatty substances) and proteins. In addition to protecting the axon, it also helps nerve signals travel quickly from one part of the body to another, or to the brain. MS attacks myelin, breaking it down and interrupting nerve signals.
Scientists believe that MS begins with inflammation. Infection-fighting white blood cells that are triggered by some unknown force enter the CNS and attack the nerve cells.
Scientists speculate that a latent virus, when activated, may cause the inflammation. A genetic trigger or an immune system malfunction may also be to blame. Whatever the spark, the white blood cells go on the offensive.
When inflammation spikes, MS is activated. Attacking white blood cells damage the myelin that protects the nerve fiber (axon). Imagine a damaged electrical cord with wires visible, and you'll have a picture of how the nerve fibers appear without myelin. This process is called demyelination.
Just like a damaged electrical cord may short out or create intermittent surges of power, a damaged nerve fiber will be less efficient at transmitting nerve impulses. This can trigger the symptoms of MS.
If you get a cut on your arm, the body forms a scab over time as the cut heals. Nerve fibers also form scar tissue in areas of myelin damage. This tissue is stiff, hard, and blocks or obstructs the flow of messages between nerves and muscles.
These areas of damage are typically called plaques or lesions and are a major signal of the presence of MS. In fact, the words "multiple sclerosis" mean "multiple scars."
During a period of inflammation, attacking white blood cells can also kill glial cells. Glial cells surround nerve cells and provide support and insulation between them. They keep nerve cells healthy and produce new myelin when it is damaged.
However, if glial cells are killed, they are less able to keep up with repair. Some of the new research for an MS cure is focused on transporting new glial cells to the site of myelin damage to help encourage reconstruction.
Myelin damage can occur anywhere in the spinal cord and/or brain, which is why MS symptoms may vary from person to person. Depending on the location and severity of the white blood cell attack, symptoms may include:
An MS episode or period of inflammatory activity can last anywhere from a few days to several months. In between, the patient usually experiences "remission" with no symptoms. During this time, the nerves will try to repair themselves, and may form new pathways to get around the damaged nerve cells. Remission can last from months to years.
There is no known cure for MS. However, current therapies can slow the disease and help control symptoms.