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An extremely brief but relevant overview of the nervous system One

What’s myelin and why is it important?

For this we need some background.

When we think of the nervous system, we generally think of two parts, first there’s the brain, called the Central Nervous System, CNS. Then there is the part that passes information to and from the brain. We call this the Peripheral Nervous System, PNS.

Nerve impulses from the body are passed along nerves by shifting chemicals. It is a slow process. Some nerves are fine with slow impulses, the nerves that cause your intestines to move food along, for instance. Then there are the nerves that must pass information very quickly.

clip_image002Imagine placing a hand on a hot stove. It wouldn’t do for the information to take a long time to get to the brain then a long time for the brain to communicate to the muscles to move the hand. The quicker the better. To do that, the fast nerves have a method to move the impulses quickly down a nerve. What happens is that the nerve is insulated with a sheath, this allows the impulse to rapidly skip down the nerve jumping long distances across the insulated portions. This insulation is called a myelin sheath.

If the myelin sheath doesn’t work properly, the nerve impulses don’t go quickly. This makes the myelin sheath extremely important. To coordinate complicated actions such as walking, running, and chewing, for examples, muscle groups need to work in complex coordinated patterns. Each muscle or set of muscles needs to contract in the proper sequence and exactly on cue. Any interruption or delay has severe consequences.

Animals and people have these important rapid transit nerves. Unfortunately, this myelin sheath can be damaged. Generally, it is the body’s own defense system that attacks this myelin sheath. It’s the same defense system that helps you conquer disease, and ward off infections. The body has a way of defining what is part of the body, named “self”, and what doesn’t belong, “non-self” which includes invading bacteria, virus, or protozoa. The body routinely attacks any “non-self” invaders and destroys them.

This “self” identification system is usually perfect. Not always, though. If the body misidentifies something that should be “self” as “non-self”, the body attacks the “non-self” with all the resources it has available. In general, it’s the immune system that is called into action. There’s also the inflammatory system which works hand in hand with the immune system to destroy invaders.

So how can this happen?

The body breaks down the invaders into small pieces. The body identifies each of these pieces, classifies them as “non-self” and produces antibodies against these pieces. This way the body can wipe out the invaders by attaching antibodies at many places. Think of an antibody like a hook. Each antibody is very specific and only attaches to the piece that it is meant to attack. The body produces a sea of these antibody hooks. If the target piece exists, the antibody hooks automatically attach and the rest of the immune system uses these hooks to help destroy the invaders.

Now suppose the system that determines “self” and “non-self” gets mixed up- or even duped. Suppose an invader doesn’t get classified as “non-self”. The body will not recognize it as an invader and will not attack it. Some bacteria will take advantage of this, they’ll coat themselves with materials that the body doesn’t recognize as foreign. Parasites disguise themselves by changing the way they present themselves, varying the expression of genes. Sometimes parasites are masters of disguise and hijack “self”-proteins in order to manipulate the immune system. The result is that if the body misinterprets what should be “self” as “non-self”, those antibody hooks will attach to normal tissue and the immune system will attack it.

This can happen with the myelin. There are several ways it can happen. Once it does happen, the immune system will break down the myelin sheaths. When that happens, myelin fragments are released into the blood stream. We test the blood for antibodies against myelin to see if those fragments are present. If they are present, we know that there is a problem.

Suppose one has a horse and that horse develops a coordination problem. Suppose it doesn’t walk well, it staggers and falls. If we test the blood and find the myelin fragments, that goes a very long way toward telling us why the horse has a problem and what to do about it.

If myelin is attacked by the immune system, all the myelin is attacked. We won’t generally see a single problem, we’ll see an array of signs-diffuse over the body. We call this array of signs “polyneuritis”. “Poly” means many, neuritis means the nerves are affected. If we’re talking about a horse, we tack on the word “equi” so we know we’re talking about the horse.