The Basal Ganglia
Although every effort has been made to make this document accurate, it is possible there are mistakes. I am fairly confident that everything is correct but since this document is made available as a courtesy it is your responsibility to catch any mistakes there might be (although I don't think there are any). That's it!! Have fun studying for the test.
So
you're probably wondering what the deal is with the basal ganglia during your
coronal sectioning. The caudate sure is
moving around and changing in size as you dissect the brain posteriorly (caudally)
and then all the sudden the globus pallidus comes from nowhere. Well in order to appreciate what's really
going on with the basal ganglia you need to understand its three-dimensional
structure which is no easy task. In
order to help in this process I've made a really crude three-dimensional movie
(it had to be low resolution so it wont take forever to download over the
web). You can view the movie at the
bottom of this page. Please read the
text very carefully before you run the movie.
There should be a control bar so you can run the movie over and
over. I would look at each structure
individually first (i.e. lentiform nucleus, caudate, and amygdala) to
appreciate its orientation in three dimensional space before trying to learn
the entire structure.
Description:
The
movie will only show the left basal ganglia.
In the beginning, a closer and closer view of the basal ganglia will be
shown. When the text comes up you will
see labels for three structures: the caudate nucleus, the lentiform nucleus
(which is composed of the globus pallidus and putamen), and the amygdala. Keep in mind that during the beginning the
persons/rats nose is facing to the right and the top of the head is at the top
of the screen. We are looking at the
left basal ganglia as if we were looking through right temple portion of the
head. As the movie progresses, you will
be given a view of the basal ganglia in several different orientations.
1)The
caudate nucleus is the tail shaped object (caudate actually means tail). You can appreciate the unusual shape of this
structure as you view it from several different orientations. At its anterior most extent it actually
extends in front (more anterior) of the lentiform nucleus. This is why it appears first in the coronal
sections. As our coronal cuts progress
more posterior, this structure progresses further from the lentiform nucleus
extending dorsally and laterally as we continue posteriorly. Eventually, this structure actually makes a
U-shaped turn and curves back into the hippocampas gyrus ending just posterior
to the amygdala. It may help to orient
yourself where the amygdala is in order to visualize the termination point of
the caudate nucleus, please look at the ventral view
of the sheep brain (the amygdala located just below the cortex in area 10).
2)
The lentiform nucleus is the large football shaped structure containing the
globus pallidus and putamen. Even
though the globus pallidus and putamen are structurally dissimilar, its easy to
see why neuroanatomists lumped the two regions together (as the lentiform
nucleus) due to the continuity between the two structures. In the movie, just the lentiform nucleus is
shown but realize that it is composed of a more medial globus pallidus and a
more lateral putamen.
3)
The amygdala is shown in this movie simply to provide a reference point for you
(i.e. just anterior to the termination point of the caudate nucleus in the
hippocampal gyrus). Its the small
sphere located at the end of the caudate nuclues. Although it is considered part of the basal ganglia there is
little functional similarity between the amygdala and the rest of the basal
ganglia. Because of this, I would
suggest not thinking of it in terms of the basal ganglia but instead think of
it as an integral part of the limbic system involved in fear.
*If you have problems running the movie look at the bottom of the
page.
Here's the movie
*If you can't run the movie you don't have Quicktime properly
installed for your web browser. To do
this go to http://www.apple.com/quicktime/download/ and download Quicktime by entering your email and name. This is the apple web site so it's safe to
download from, just make sure you do not choose any of the news items or you'll
probably get junk e-mail (by default you will not get the news). Install Quicktime using the installer file
you just downloaded. Now go to your
Quicktime Folder and open the Plugins Folder.
If you have a PC put the "npqtplugin.dll" file in the Plug-ins
folder of your web browser. If you have
a Mac put the "QuickTime Plugin" file in the Plug-ins folder of your
web browser. Now restart your web
browser and everything should be fine.