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  1. #1
    Senior Member Scott Buxton's Avatar
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    individual phone wires or a thick wire ?

    Is the spinal cord more like a bundle of individual phone wires or a thick wire which is fed via a bunch of small wires and then splits into another bunch of small wires?

    If the latter. how does stem cell therapy find the correct output nerves from the spinal cord?

    If the former, are the nerves that connect the systems (so AD is less likely) some of the first to connect?

    Thanks. Scott.

  2. #2
    Hi Scott,

    Be prepared for lots of reading.
    Here is a website that explains what the spinal cord is http://faculty.washington.edu/chudler/spinal.html

    and a more indepth website here. http://en.wikipedia.org/wiki/Spinal_cord


    As for your question regarding stem cells, I'm not sure and it is all experimental. But it sounds very promising. For some reason, when the stem cells come in contact with the damaged or dead cell they bring it back to life.

    Here is a quote from this website that kind of explains it

    Serving as a sort of repair system for the body, they can theoretically divide without limit to replenish other cells as long as the person or animal is still alive. When a stem cell divides, each new cell has the potential to either remain a stem cell or become another type of cell with a more specialized function, such as a muscle cell, a red blood cell, or a brain cell.
    http://stemcells.nih.gov/info/basics/

  3. #3
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    The spinal cord would be the cable that the individual wires are contained within.

  4. #4
    Quote Originally Posted by eagle18
    The spinal cord would be the cable that the individual wires are contained within.
    That is a simplistic model.
    Daniel

  5. #5
    Quote Originally Posted by Scott Buxton
    Is the spinal cord more like a bundle of individual phone wires or a thick wire which is fed via a bunch of small wires and then splits into another bunch of small wires?

    If the latter. how does stem cell therapy find the correct output nerves from the spinal cord?

    If the former, are the nerves that connect the systems (so AD is less likely) some of the first to connect?

    Thanks. Scott.
    Scott,

    What a great series of questions! Let me add some information that may help you understand better.

    1. The human spinal cord normally has about 20 million axons (nerve fibers) going up (sensory) and down (motor). Probably less than half of these are myelinated (covered with myelin) and go all the way to and from the brain. Axons that are not myelinated cannot be easily seen on a light microscope which has a resolution of about 1-2 microns (1 mm = 1000 microns). Note that a cat normally has about 500,000 axons that are countable with light microscopes and about 40,000 axons are necessary and sufficient for walking. A rat has about 50,000 myelinated axons and probably less than 10,000 are necessary and sufficient for a rat to walk.

    2. Stem cells are just cells that can make many different kinds of cells, including itself. A progenitor or precursor cell is a cell that can make other kinds of cells but not itself. A neural stem cell is a stem cell that can make cells of the nervous system, including neurons, astrocytes, oligodendroglia (the cells that form myelin).

    3. When stem cells are transplanted into the spinal cord, they often do not know what to do. Depending on the signals that they receive from surrounding cells, they may produce growth factors that can stimulate axons to regrow. They may produce astrocytes that bridge the injury site, providing a pathway for axons to grow. They may produce oligodendroglial cells that remyelinate axons. They may make neurons that replace neurons that have been damaged. Or they may do nothing. By the way, if a transplanted cell produces an inappropriate number or types of cells, we would call such a cell a cancer or tumor.

    4. Axons in the spinal cord can be divided into four major categories. These fibers often do sprout after spinal cord injury and can make aberrant connections.
    • Somatosensory - these are fibers that carry signals from the skin, joints, muscles to the brain.
    • Motor - these are fibers that carry signals from the brain and spinal cord to the lower spinal cord, connecting with spinal motoneurons (the neurons that connect with muscles) and interneurons (the neurons that connect with other neurons).
    • Autonomic sensory - these are fibers that carry information from spinal sympathetic and parasympathetic neurons to the brain.
    • Sympathomotor - these are fibers that carry information to sympathetic centers in the spinal cord. These fibers often contain catecholamine neurotransmitters (such as epinephrine and norepinephrine).

    5. Spinal circuits that have been disconnected from the brain often become hyperexcitable. In the motor system, we know this as spasticity. Likewise, brain and upper spinal cord circuits that are disconnected from the spinal cord below the injury site often become hyperexcitable and this may lead to neuropathic pain. Similarly, autonomic functions such as blood pressure, sweating, and blood flow may be disconnected by the spinal cord injury and manifest as autonomic dysreflexia (AD).

    I hope that this is helpful.

    Wise.

    P.S. The 20 million number of axons in human spinal cord is actually quite hard to come by number. It comes from an out of print book called Facts and Figures of the Brain published in the 1960's (I have the book on my bookshelf somewhere and will find the reference) by two Russian scientists who summarized many early studies that counted neurons and axons in the brain and spinal cord.

    The number makes sense, however, if you consider the following:
    • A typical myelinated axon is 2-20 microns in diameter. One millimeter is 1000 microns. Therefore, each axon occupies 4-400 square microns in area.
    • One square millimeter has 1,000,000 square microns and therefore can hold 2,500-250,000 axons.
    • The thoracic human spinal cord is about 14 mm in diameter (the thickness of your pinky) and therefore has an area of about 150 square mm.
    • If 100 square mm of the spinal cord is devoted to ascending and descending axons, this means that the spinal cord can hold 250,000 to 25,000,000 axons, depending on the thickness of the axons.

    Here are some addition resources about spinal cord injury that you might want for bedtime reading:
    http://www.jyi.org/research/re.php?id=336
    http://www.ninds.nih.gov/disorders/sci/detail_sci.htm
    http://darwin.nap.edu/books/0309095859/html
    http://www.mrc.uidaho.edu/~rwells/te...System%20I.pdf
    Last edited by Wise Young; 06-02-2006 at 05:58 AM.

  6. #6
    Senior Member justadildo's Avatar
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    ......think fibre optic cable......thousands of threads bundled together in one small cable

  7. #7
    Senior Member Scott Buxton's Avatar
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    Thank you for educating me on this!

    Thank you for educating me on this! I recently moved here so don't yet have a library card, but an association which helps people with SCIs, said that it could get the books for its library, hence my bedtime and many-other-times! reading. Scott.

  8. #8
    Quote Originally Posted by Scott Buxton
    Thank you for educating me on this! I recently moved here so don't yet have a library card, but an association which helps people with SCIs, said that it could get the books for its library, hence my bedtime and many-other-times! reading. Scott.
    You are welcome. Please keep asking questions because I don't know what people don't know. Note that some of the views that I am expressing may not be mainstream. I keep hoping that we can get some other scientists on board to comment as well.

    Wise.

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