Let us now move on and look at the meninges
of the brain and also the spinal cord.
Here is a section on the left hand side showing
you a section through the skull, skin on the
surface, the bone of the skull and then underlying
is connective tissue. The periosteum is the
capsule that lines the surface of bones and
that is continous with the outer layer or
the outer meningial layer of the brain, the
dura. The dura mater is really almost part
of the periosteum. It is the outside covering
of the brain. And on the image on the right
hand side, this is the section through some
neural tissue happens to be the optic tract,
but it is a good section to illustrate these
meningeal layers. And on the outside it is
very thick connective tissue, which is the
dura mater. When you have the arachnoid layer,
the arachnoid layer has peeled away from the
surface of the dura here and that surface
of the dura between the arachnoid and the
dura is often called the subdural layer, it
is an artificial space. Underneath the arachnoid
layer is the sub-arachnoid space and on the
diagram, you can see that that's a fairly large
space indeed. It is full of cerebrospinal
fluid that circulates around the brain and
keeps the brain protected and buoyant and
also flows around the spinal cord. The sub-arachnoid
space also houses some of the large vessels
before they pass into the deep substance
of the brain. And then the most internal covering
around brain tissue is the pia mater. It forms
almost an epithelial surface on the surface
of the brain tissue and penetrates some distance
into the neural tissue particularly carrying
very small blood vessels.
Well lastly let us look at the ventricles of the
brain. You know the brain has big spaces in
it and these big spaces are occupied by cerebrospinal
fluid. Here you see some ventricles, one on
the horizontal section through the brain you
saw earlier, huge spaces between brain tissue
and on the right hand side, you see it labeled
in a histological section. The pink stained
region that you see above and below the
label are neural tissue. But in those ventricle
spaces, you can just see some tissue evident.
That is called the choroid plexus. The choroid
plexus is an extension of the pia wrapping
around groups of little blood capillaries.
And that choroid plexus produces the cerebrospinal
fluid and I said it circulates in the sub-arachnoid
space, through all these ventricles, along the
spinal cord, and finally it returns to the
vascular system to the venous system through
structures called arachnoid granulations.
Well under high power, on the right hand side, you
can see these choroid plexuses within the
ventricle. And again that remind you they are
just really extensions of the pia wrapping
around very very small groups of blood capillaries.
And those epithelial cells that formed the choroid
plexus are responsible for making the cerebrospinal
fluid. The very complex mechanism they
use and that is one that I won't explain now.
So let us now summarize what we have just been
looking at. Make sure you are aware of the
structure of the peripheral nerve, its wrappings,
its connective tissue coverings.
Make sure you appreciate the complexity of both the cerebral
cortex and the cerebellar cortex, the different
cell layers. Make sure you know the different
glial cells, recogonize them and know their
functions. And finally appreciate the coverings
of the brain that protect the brain and the
spinal cord. The dura, the arachnoid and the pia.
So thank you very much for listening to this
lecture. I hope you have enjoyed learning
something about the structure of the peripheral
nerve and also a little brief overview of
the histological structure of the brain.