Hop, Walk or Run?

kangaroo-clip-art
After years of reading about MS, I found myself unable to answer a very basic question. What exactly is attacked by our nervous system in MS? As I was trying to define how MS attacks, I realized I didn’t know the answer to a very basic question. With MS, does our immune system target our nerves or “just” the myelin sheaths? I’ve used this for a basic understanding for years: http://www.ms-gateway.com/my-life-with-ms/introduction/what-is-ms-179.htm

The link says, “demyelinated axons, however, cannot conduct electrical impulses efficiently. When nerve fibres have been stripped, i.e. have been demyelinated, they may begin to “short circuit” or fail to properly transmit signals within the nervous system. Thus, when myelin sheaths are damaged, impulses are slower than they used to be. Messages then have to be passed on along the entire length of the nerve fibres which is much slower than if impulses could still jump from node to node.
Transmission is slowed or even blocked.”

I was then looking at http://www.unm.edu/~jimmy/myelin_sheath.jpg which gives a great graphical representation of the myelin sheath and a cross section of a nerve.

Given that the impulses travel more readily by jumping along the outer membrane of the myelin sheath and often fail completely without the myelin, why do we think our nerve signals ever naturally travel the length of the nerve fibers instead of traveling along the outer membrane of the myelin sheath?

Heather on Patients like me gave me the answers I was seeking. We have unmyelinated nerves which conduct signals. I finally got the an answer which fits in my head too when Heather explained the signals traveling faster when hopping from point to point. Now I picture my nerve signals like a kangaroo. I imagine timing a walking kangaroo in a race against a hopping one. I can also look at footsteps in the dirt. When we run, our steps are further apart. With these two images in my head, I can understand how a signal might travel faster jumping between the nodes in the myelin sheath.

Thread on Patients Like Me: https://www.patientslikeme.com/forum/ms/topics/125826

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