Well let us move on
and look at the brain. Only certain parts
of the brain are going to be described. First
of all, when we look at the brain as we see
in the left-hand image here, this is the part
of the brain or at least it is the brain has
been sectioned horizontally. You are looking
at a horizontal section through the whole
brain whereas on the right-hand side, you
can see the brain that has been sectioned
mid-sagittal, it has been cut down the center.
So you see the top part and the bottom part
and even part of the spinal cord. But what I want
to bring to your attention is the gray matter
of the brain is actually on the outside, whereas
remember, in the spinal cord it was that H
or butterfly-shaped structure on the inside
surrounded by white matter. In the brain,
it is the other way around, the white matter
is internal to the gray matter. Now if you
look very very carefully in these sections
through the brain, the one that's taken
horizontally, you can see some gray matter
or grey stained components within embedded in
the center of the brain, embedded in the center
of the white matter. They are called nuclei.
And this is a nucleus in the brain that is
called the thalamus. Now, when we refer to
the cerebral cortex and also the cerebellar
cortex, we really mean the gray matter of
the brain. This is a cerebral cortex shown
on the right-hand side that happens to passes the
frontal lobe of the brain and there is a cerebellar
cortex at the back or base part of the brain.
They are two different components of the brain,
two very important major regions of the brain.
Notice that cerebral cortex is very folded
and so it is the cerebellar cortex. It is a way
of making sure that there is a massive surface
area for all the cortex to have many many
neurons that are going to perform very important
functions. So then the gray matter is on the
outside and the white matter is on the inside
of the brain. And on the right-hand side, you
can see a microscopic image of a region
taken through the gray matter and the white
matter or the cortex as well. Again remind
yourself that a nucleus is a massive gray
matter within the white matter of the brain.
But now on the right hand side of the cortex,
now try and find a region that is gray matter.
That region labeled there is on the edge of
the brain surface. The surface of the brain
is that white clear area in between that brain
tissue. You are looking between one of these
major convolutions or increased surface area
regions of the brain. The white matter is
internal as I've emphasized a couple of times.
So let us have a look inside that gray matter.
Shown here on the left hand side is the cortex
and the dark brown region is a layer of cells
that are very important, a layer of neurons
and they are called the pyramidal cell. And
they're cells within the gray matter that talk
to the ventral horn cells in the spinal cord.
They are the ones that initiate the ventral
horn cells to bring about contraction of skeletal
muscle. Neuropil refers to the part of the
neural tissue that is occupied by unmyelinated
axons, by dendrites and by glial cells.
So I just put that word up there just so if you
hear it again or I mentioned it again in subsequent
lectures and it refers to those supporting
components of the tissue. The glial cells
plus also dendrites and unmyelinated axons.
The real focus is the main neuron and in this
case it is a pyramidal cell. Well this is the
cerebral cortex taken in this mid-sagittal
section, we looked at the section through
one of those convolutions or one of those
gyrus they call, the folded portions of the
cerebral cortex. Now let us have a look at
the cerebellar cortex. Cerebellar cortex is
shown, when viewed with a microscope, on the
right hand side, stained to show the white
matter and also the gray matter.
The gray matter remember is on the outside of
this very very complex folded cortex. And if we
look inside that gray matter on a higher magnification,
we can see that within the gray matter, there
are a number of layers of neurons. The cerebellar
cortex is made up of three different layers
of cells and the most important one is the
Purkinje layer in the center. That Purkinje
cell layer is a layer of cells that has an
enormous dendritic branching pattern.
It receives a lot of information from other parts of
the brain and then sends its message via one axon
further on. So they are just examples of some
of the very complex neurocomponents of the
brain, the cerebral cortex and the cerebellar cortex.