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I'm studying the motor pathways of the brain and I'm a bit confused about how the lateral corticospinal tract descends.

From Neuroanatomy: Text and Atlas by Martin, J. H., 4th edition, right before Figure 10-4:

Some of these [terminating] axons descend ipsilaterally; many descend contra-laterally and re-cross midline within the gray matter in lamina 10. The function of these ipsilateral axons is not well understood.

I understand that the axons cross over at the Pyramidal decussation, but this paragraph is really confusing me. What descent is being referenced here? Is it descending in the spinal chord? Alternatively, is the paragraph implying that some axons don't decussate in the pyramidal decussation?

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  • $\begingroup$ Can you provide a page number and tell us what edition of Martin you're using? $\endgroup$ – Susan Oct 18 '14 at 14:42
  • $\begingroup$ @Susan Fixed. Unfortunately, I can't give you a page number because I'm using the Kindle edition of the textbook. I tried to give the most accurate reference I could. $\endgroup$ – Seanny123 Oct 18 '14 at 14:44
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The answer ends up being on the next page when discussing the ventral corticospinal tract.

Many ventral corticospinal tract axons have branches that decussate in the spinal cord, similar to the re-crossed lateral coticospinal tract axons described earlier.

In other words, some axons of the lateral corticospinal tract ignore the pyramidal decussation, join the anterior corticospinal tract (which then synapses bilaterally later at the spinal commissure).

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