CLASS DISCUSSION

Module 5

Probably the most common site of damage to the pyramidal tract (and associated descending motor pathways) is the internal capsule. It is a difficult region to visualize, so lets start by looking at some gross brain dissections. Begin by calling up Figure 1-46 and leaving it on the screen as we go forward. Imagine that you have decided to expose the corona radiata and internal capsule by gradually removing more lateral tissue. We start with a lateral view, diganat_1b.jpg and remove the overlying lobes to expose the insula diganat_2a.jpg . Next we scrape off the insular cortex, the extreme capsule and the claustrum; now, diganat_2b.jpg , we see the external capsule covering the putamen (posteriorly) and the exposed lateral surface of the putamen (anteriorly) . Next , the lateral surface of the putamen is completely exposed diganat_2c.jpg. Removing tissue above the putamen exposes the corona radiata diganat_2d.jpg. Stop to check where we are on Figure 1.46. Now. we shell out the putamen and globus pallidus to reveal the internal capsule in diganat_2e.jpg . By removing more brain tissue, we can trace the descending fibers of the internal capsule down to form the cerebral peduncle diganat_2f.jpg . If you cheat a little and click on "label all" you will see we have traced the pyramidal tract all the way from the cortex to the pyramids of the medulla. But why in the world haven't we seen the caudate nucleus? Check Figure 1-46 for the answer.

We are about to trace descending pathways, but first we want to make 2 points:

__________ 1) In general the best way to trace a descending pathway is to call up the most rostral slide of the series, and then use the "key" descending button to step through the series.

__________ 2) You simply cannot actually see most of the pathways we will be tracing. We have used a variety of labels to show where they are, and you should have a general idea of how they pass through the tegmentum of the brainstem. But we will never point to a seemingly empty spot in a slide and ask "name this pathway". What we might do, however, is point to the lateral part of the medulla and ask "What somatic sensory pathway ascends in this region?" If you want a better feel for this, try the practice practical that can be called up from the "I want to" page.

1) The pyramidal tract in the internal capsule - Figure 5-11 - start with slide 8

2) The pyramidal tract (and others) descends through the brainstem - start with Slide 28 and descend

3) The corticobulbar pathway - go thru the above series again and "follow the yellow dots" (this isn't Kansas).

4) The cortico-rubro-spinal pathway - Slide 28 - then descend

5) The cortico-reticulo-spinal pathway - Slide 24 - then descend, following the green dots

6) The tectospinal and vestibulospinal tracts - Figure 5-1 - reminds you of how they fit in the big picture -then start with Slide 20 and descend

We concede that our views of the above pathways, as they descend in the spinal cord aren't very good. For better ones, look at Blumenfeld's Figure 7.4 or Haines's Figure 9-12

7) Clinical Problem 8 - before you start, review the syndromes associated with damage to upper and lower motor neurons

PIX BRAIN HOME _ _ MOD 5 HOME _ _ I WANT TO