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After wading through a sea of information, I understand the main differences between the white matter and grey matter of the spinal cord.

I know that white matter contains myelinated axons in the ascending and descending nerve tracts from the brain to the spinal cord. I know that grey matter contains somata which contribute to sensory and motor functions from and to the peripheral nerve fibers.

With the differences in mind, I am confused about the relationship between the two.

The main question being: What signaling, if any, takes place between the myelinated axons of white matter and the somata of grey matter? More pointedly, do the myelinated axons from the nerve tracts in white matter ever synapse with dendrites from somata in grey matter?

My guess is yes, that this is a key aspect in how the brain and the spinal cord communicate. But I haven’t yet found any definitive source that addresses this question directly.

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This is kind of a big question, as there are lots of different pathways that synapse at different levels and some of the cell bodies send axons over long distances. Is there a particular tract that you are interested in? –  jonsca Jul 11 '12 at 2:09
    
I am studying Excercise Physiology, for the purposes of personal training, from that vantage point I am trying to solidify a big picture understanding mostly. So no i don't have to know the nitty gritty of a particular tract, my texts and resources have illustrated the big differences between the white and grey matter and thier main functions but do not really address what if any signaling takes place between each other. I was guessing and take it from your answer they do. Is there a typical pattern or does each pathway feature a unique setup between the white and grey matter? –  user972 Jul 11 '12 at 16:08
    
That should give you a start. You can read up on these and some of the other tracts and see if you have specific questions on them. –  jonsca Jul 11 '12 at 16:59
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Here is a great diagram (from here) that outlines all of the different white matter tracts running up (blue) and down (red) the cord. enter image description here

The portion in the center, as you have found in your research, is the gray matter. In there are the different interneurons (cells that exist in the network to integrate information from descending controls and do further processing on it) and all of the different motor neurons. The corticospinal tract descends to the appropriate level (for example, a neuron in charge of moving your arm, to keep it simple, will have a cell body in the brain, and descend to the thoracic level), enters into the gray matter and either synapse on an interneuron or directly onto a motor neuron).

The sensory neurons are a slightly different animal. Some (pseudo-unipolar cells) have what are basically two "legs", one that runs out into the periphery, which will take the signal from something like a Pacinian corpuscle in the skin, propagates a signal to the cell body, which is outside of the spinal cord in the dorsal root (see below), and the other "leg" runs all the way up the dorsal column into the medulla of the brainstem.

enter image description here

from here

So that should give you some idea of the two major tracts. To see some of the finer detail, you can look into the different layers (laminae) that the gray matter is composed of, so that you can trace the connections all the way in.

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Thank you! Very informative. –  user972 Jul 11 '12 at 22:08
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