Voiceover: In this video, I'm gonna talk about
gray and white matter. In the central nervous system, which is mostly the brain
and the spinal cord, there are areas called "gray matter" gray matter, that contain most of the "neuron somas". So most of the neuron somas
in the central nervous system are found in the gray matter. And then there are other
areas called "white matter". And the white matter of
the central nervous system, is most of the "myelinated axons". Myelinated, so axons that
are wrapped in myelin. Myelinated axons. And these are actually
kinda funny names for these parts of the central nervous system because they're really not gray or white. They're all kind of different
tan colors, in life. But when the tissue is
prepared certain ways after being removed from the body, it can have a grayish appearance or a more whitish appearance. And so these are the names that have stuck for these general areas, the gray matter and the white matter. Now, the distribution of
gray matter and white matter is a little different between
the spinal cord and the brain. If we look first at the spinal cord here, and here we have a
really nice illustration of some different sections
of the spinal cord. So right over here. What these drawings represent are different levels of the spinal cord. Like if we made little sections of it. Like if we were cutting a loaf of bread and kind of cut from the
top down to the bottom. And then we're looking down at
these sections from the top, so that we're kind of
looking down this way at the different sections
over here in these drawings. And what we see in the spinal cord is that most of the gray
matter of the spinal cord is on the inside, this kind of "H" shape or this butterfly shape of gray matter. And the white matter of the spinal cord is mostly on the outside, all this stuff outside of
this "H" shape of gray matter. And it's a little hard
to see on these drawings, so let me just take, like
this one, for example and let me just draw it
here, just a little bigger. So I'll just draw kind of an oval like we're looking down at the top of a section of the spinal cord. And on the inside is
gonna be the gray matter, that's gonna be in this kind of "H" shape or this butterfly shape. Let me just draw the back part, here. And all of this stuff
would be gray matter. So, it would be lots of neuron somas that would give it a different color from the white matter on the outside. Let me just draw in a little bit of white right here on the outside, because that's how the
spinal cord is set up, with most of it's myelinated axons forming white matter on the outside. Except for this little bit here where the gray matter goes to the very
back of the spinal cord. Now, for the brain,
it's a little different than it is for the spinal cord. So let's take a look at the brain and make it a little bigger
with this drawing over here. And on this drawing,
we're gonna be looking at the brain from the left side. Let me just write that up here. So this is the brain from the left side, like we're looking over
this way at the brain, with the cerebrum on top and the cerebellum back here, and then the brain stem, we just see a little bit right here. And then this drawing is gonna be of kinda the inside of the brain, like if we cut along the
brain kinda like this, through a bunch of the
cerebrum and the brain stem. And we're kind of looking
at it from the front. So we're looking at it this way, after cutting it through here, so that we can look at the
inside of the brain tissue. Now, where the spinal cord had gray matter mostly on the inside, the brain actually has gray matter mostly on the outside. So here you can see this
layer of gray matter that's going all the
way around the outside of the cerebrum here. And this layer of gray
matter on the outside of most of the brain, is called "cortex". Cortex. And this cortex covering
the surface of the cerebrum is called the cerebral cortex. And the cortex covering
the cerebellum down here, is called the cerebellar cortex. And that's all gray matter on the outside of those parts of the brain that contain most of the neuron somas. I'll just draw some little circles here to represent neuron somas. Although, they're actually
much smaller than this, if we did it to scale. And also, kind of the
reverse of the spinal cord, where most of the white matter was on the outside of the spinal cord, most of the white matter of
the brain is on the inside. So this lighter colored stuff here, under the cerebral cortex,
this is all white matter deep inside the cerebrum and white matter down
here in the brain stem. Now, there are some other areas deep in the brain that are gray matter, that contain lot's of neuron
somas, like this right here. And instead of calling
these areas "cortex", like the gray matter on the outside, the gray matter that's
kinda deep in the brain, we call "nuclei". One would be a "nucleus"
and multiple is "nuclei". And there are multiple
nuclei deep in the brain, these areas of gray matter. Like here are several right here, and here's another one right here. Now, in the white matter of
the central nervous system, are collections of axons that are traveling together
to different areas. I'll just draw a dash line to show that these axons are gonna keep going. But there are multiple neuron-axons that are kind of traveling together. They're starting in a similar area and they're heading to a similar area somewhere else in the
central nervous system. And collections of
axons traveling together in the central nervous
system, we call "tracts". Tracts. So this would be one tract, right here. And a tract could have
many, many axons in it carrying, often a very
similar kind of information from one part of the
central nervous system to another part of the
central nervous system. The central nervous system has a huge number of neurons in it, doing
lots of different functions. In addition to neurons involved in motor, sensory, and automatic functions, like we talked about with the
peripheral nervous system, the central nervous system
also has lots of neurons participating in the higher
functions of the nervous system. That is, participating in cognition, emotion and consciousnesses. And that's particularly
in the cerebral cortex, all this gray matter on the
outside of the cerebrum. And certain other parts of
the brain are very involved in those higher functions of
the nervous system, as well.