Myelin

[annedocuk]

Does anyone know how much myelin there is in the brain that can potentially be damaged compared to the spine? I just had to have a brain MRI for very odd visual disturbances (has been put down to old scarring). In the last 2 years I have only 1 new brain lesion which is great! However I have lots of new symptoms-in particular bladder and lower limbs. So is there more myelin in the spine or the brain and by how much. Tried looking it up but can not find an answer.

[MrsBones]

I can't specifically answer your question. The thing to remember, though, is that any lesion in the cord can mean more trouble than the same sized lesion in the brain, regardless of myelin proportions.

Your cord is about as big around as your thumb. Take a look at your thumb now. Imagine a lesion that covers one side of it. See how much of your thumb is unaffected? Now imagine that same lesion in your brain. See how much brain tissue is unaffected?

In spinal cord lesions, like SCI, anything below them is effected.The brain has far more opportunity to reroute and adjust to damage. The cord is limited. Regardless of how much undamaged cord there is, once there is a lesion, the area effected is essentially like a kinked hose as far as impulse conduction goes. Only some of the info is getting through, with no chance to find another route.

So, really, the total amounts of myelin in one or the other, doesn't much matter for the purposes of the potential for symptoms and functional impairments. It's more the fact that any lesion in the spine essentially "blocks" everything below it. You'd only need to be concerned with the amount of undamaged myelin in the cross section of cord that has a lesion in it. A small lesion on one side of the cord, for example, would have less of an effect than one that a large transverse one.

[foxz71]

It's not so much "how much" that would answer your question. It's more about the location of the lesions. The Myelin is the sheath that protects the nerves; so my guess is that there is a whole heck of a lot of it. But there are some people with 30+ lesions that have few symptoms and there are others with only a few lesions that have debilitating symptoms. If you look up "white matter lesions" you will find a host of information on the topic.

[salamandertom]

Hi. Myelin is the coating covering the axon of a neuron. This is what speeds up the signals that our brains send and recieve. With damage to this, the signal can not send at all or be confused.

Myelin can be repaired sometimes if the inflammation stops. Personally I have yet to have that happen, but it does happen.

In your spinal cord, like the above poster said, there is a lot less areas to reroute. I would also like to point out that in your spinal cord there are not new neurons to reroute to even if there were the room. These are interneurons (typically) and they are very long. In our brains there are a lot of neurons and they can change who sends what signal b/c of that. In our spinal cord these neurons are really more for *transmission* than sending and recieving.

For example, you touch a hot stove. The sensory neurons in your hand change that into a pain signal that travels to the dorsal root ganglion and meets with an interneuron which sends it up the spine and into your brain. The brain sends it to various parts of the brain, interprets it, and sends another signal back down the spinal cord which eventually gets sent to a reflex area and you react. Now the neuron that carried the signal afferently probably is not the descending neuron. I haven't studied the pathway in enough detail to know for sure, but I would guess no.

Anyhow, there are limited neurons in our spinal cords and they are like the middle men. Unfortunetly we cannot function well without the middle man.

[Greg]

I have no clue about how much myelin there is, but I did see something on mslearn that stated that the same area of the spine was responsible for bladder, bowel, and sexual function. I am sure that there is a area or areas in the brain that also could effect those functions. But the spine was specifically mentioned with ms sx of these functions.

[0485c10]

Bladder dysfunction is the neck, i've been told.
maybe you had new lesions in the neck which is why they weren't in the brain. The most average progression of ms is from the brain to the neck then down the spine...

thasts the average progression--ms isn't aversge sop i am certain more than a few can post a different progression...

re mylen in the brain & spine. the brain has the ability to route around damage areas, the brain is plastic and can do that but the spine can't.

then something i don't understand but have read. brain lesions in the grey matter cause more visible damage than brain lesions in the white matter. spine tissue is all grey matter. i don't have a great understanding of gry matter versus white matter.

[salamandertom]

The part of the spinal cord that transmits signals from sensory and motor neurons is white matter. Gray matter is the part of the brain that processes the information and decides what to do with it. Lesions in this area I would imagine are much more serious than in the white matter of the brain.

The biggest problem with spinal cord lesions is that when you have them any function at that level or below *can* be affected by that lesion. I have all my spinal lesions in my c-spine or neck, but any functions that are on the area of that lesion or below could be affected. This is what is happening in my case.

[0485c10]

The part of the spinal cord that transmits signals from sensory and motor neurons is white matter. Gray matter is the part of the brain that processes the information and decides what to do with it. Lesions in this area I would imagine are much more serious than in the white matter of the brain.

i don't know the difference between grey white matter entirely, but this does not sound all inclusive or entirely correct, in other words i think you have a piece but not the entire puzzle. begin researching it-it will drive you crazy. its not as easy as you think or as easy to categorize.

white matter is called while matter because it appears white from the myelin. grey matter is called grey because it doesn't have this white coloring and it appears grey. there is grey matter in the outer portion of the brain and spine tissue also appears grey.

[salamandertom]

Hi, I am copying right out of my textbook (Human Anatomy and Phisology, 8th edition, Pearson)

"The basic pattern of the CNS consists of a centeral cavity surrounded by gray matter (mostly neuron cell bodies), external to which is white matter (myelinated fiber tracts)."

There is gray matter in the spinal cord, but it recieves signals from the brain, from the white matter of the spinal cord. At least that is what I was taught.

You are right, it is maddening trying to understand it all. But, what I am saying about the gray matter processing information is correct. The white matter transmits and the gray matter processes and interprets. The myelin is what causes the whitish appearance, but there are axons that are not myelinated in the white matter.

[0485c10]

Yes it is confusing. i re-looked at some sites with your comment in mind-i think its one of those things i can focus on and understand for 5 minutes then its gone.
Dendrites are on the soma and also an the end of the axon?.
it looked like 2x dendrites which need 2 soma's if soma's only have dendrites? but if both soma and axons have dendrites there could be a single processor not dual processors?

neurons in grey matter consist of neuronal cell bodies plus their dendrites.
in contrast with the neurons of the white matter, grey matter neurons do not contain long axons(myelen coated) that transmit to more distant regions of the cns.

40% of brain is made of grey matter and 60% of grey matter. but grey matter consumes about 94% of the oxygen the brain uses.

the majority of MS lesions occur in the white matter but about 5% occur in the grey matter.

well look at that, there is more than 1 kind of neuron. grey matter neurons & a white matter neurons. and they differ.

somehow i think this subject ls like peeling an onion for me, i just peeled one more layer of confusion with many more layers to go.

[0485c10]

40% of brain is made of grey matter and 60% of grey matter.

.

Correction: "40% of brain is made of grey matter and 60% of white matter"