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- [Instructor] So in this video,

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we're going to talk about two
systems of supplying nutrients

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and removing waste from the brain.

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One is cerebrospinal fluid.

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The other is blood.

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So when we look at how the
brain sits within the skull,

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you have to remember that the brain

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is going to be floating
in cerebrospinal fluid.

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It helps give the brain buoyancy.

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It makes it feel a little
or seem a little lighter.

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And in order to prevent the brain

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from bouncing around too
much inside of the skull,

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we're going to see that there are

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two very tough connective
tissue membranes,

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one called the falx cerebri.

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And this is the falx cerebri here.

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And the purpose of the falx cerebri,

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as you can see in this model,
is to be able to separate

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the left and the right hemispheres,
and to prevent the brain

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from moving too much from side to side.

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In the next specimen,

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we'll see that there is
another thick membrane

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that you have to look deep inside here.

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And this membrane rests right here,

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right above the cerebellum.

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And it's called the tentorium cerebellum.

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And what it does is it creates

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an upper cranial cavity
and a lower cranial cavity.

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The upper cranial cavity is
going to contain my cerebrum,

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and the lower cranial
cavity here is going to have

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my brainstem and cerebellum.

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This is not the foramen magnum.

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This space is not the foramen magnum.

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If I keep going to the opposite side,

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you can see the foramen
magnum on the bottom.

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So the upper cranial cavity
contains the cerebrum.

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The lower cranial cavity contains

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the brainstem and cerebellum.

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So this is another
sagittal cut of the brain.

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And again, we can see

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what we call the falx cerebri

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that separates the two hemispheres,

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but something that we couldn't
see on the last specimen

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was the tentorium cerebellum.

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The tentorium cerebellum
essentially separates

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my occipital lobe from my cerebellum.

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So the other thing that's
good about this specimen

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is that we can see the meninges.

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The meninges, the dura mater
that we saw in the spinal cord

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is this outer meningeal layer.

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There's three layers of
meninges: dura mater.

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Attached to it, so I really
can't separate the two,

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attached right to it
is the arachnoid mater.

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Then under the arachnoid
mater, there is this space.

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It's called the subarachnoid space.

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And this entire
subarachnoid space is filled

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with cerebrospinal fluid,

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and that's how the brain floats in.

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The third meningeal layer you can't see

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because it's a single cell layer thick.

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It's called the pia mater,

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and the pia mater
surrounds all the cerebrum,

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dipping into all of the sulci.

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Now something that you
might see right here

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is this little hole.

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This is a sinus.

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We're going to call this,

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these were dural septa.

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Septa separate the brain into cavities.

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This dural sinus is going
to have venous-filled blood,

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low oxygenated, nutrient-low blood

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that's going to go down
through my jugular vein

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in order to go to the heart
and be pumped to the lungs,

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reoxygenated, and then go out to the body.

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Not only is the brain surrounded

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by the three meninges, the dura mater,

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the arachnoid mater and the pia mater,

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the spinal cord is also
surrounded by the dura.

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And you can't see it here,

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but the inside would be the arachnoid.

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And underneath that would
be the subarachnoid space

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filled with cerebrospinal fluid.

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So just like the brain

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floats in CSF,

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the spinal cord floats in CSF.

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So in the brain, we have two dural septa.

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We have the falx cerebri
and the tentorium cerebellum

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that prevents the brain
moving around too much.

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Here in the spinal cord,

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remember that we called this
connective tissue structure

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that went from the conus medullaris,

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the end of the spinal cord
to the end of the dural sac

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the filum terminale,

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and the filum terminale

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is like the dural septa
of the spinal cord.

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So now let's take a look at
the ventricles from the inside.

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So we said that the subarachnoid space

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had cerebrospinal fluid that
allowed the brain to float in.

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We also are going to have
these holes in our head

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called the ventricles,

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and these ventricles
are going to be filled

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with cerebrospinal fluid.

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Now this model is showing the fluid.

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What's solid here would actually
be liquid inside the brain.

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You have two lateral ventricles,

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one for your right hemisphere,

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and I know this is my right hemisphere

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'cause again, this is my temporal lobe.

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And look at the curved
part of my temporal lobe.

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Since it's on the right, this
would be a right hemisphere,

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and we have a lateral ventricle
for the left hemisphere.

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We have a ventricle for the
frontal lobe, the parietal lobe,

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the occipital lobe and the temporal lobe.

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And that's because cerebrospinal
fluid is one of the systems

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that's going to provide
nutrients to my brain.

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The lateral ventricles are going to drain

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through a small structure here

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called the interventricular foramen.

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Inter means between, ventricular,

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and foramen means a hole.

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And where that's going to
drain is it's going to drain

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into a small ventricle right here.

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This ventricle is called
the third ventricle.

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And the third ventricle
is the perfect landmark

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for your thalamus and hypothalamus.

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It will then drain
through an even smaller,

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I'm not sure if you'll be able
to get it on the video here,

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an even smaller canal

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called the cerebral aqueduct.

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And from the cerebral aqueduct,

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it will drain into this structure here

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called the fourth ventricle.

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And the fourth ventricle is a landmark

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for the pons and the medulla.

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The cerebral aqueduct

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is a perfect landmark for the midbrain,

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but the fourth ventricle is a landmark

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for the pons and the medulla.

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So now let's take a look at
this in a real brain specimen.

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So I've got my corpus callosum here,

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and there is a membrane, it's
called the septum pellucidum.

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We won't learn it in this class,

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but the septum pellucidum is a membrane

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that separates my left ventricle
from my right ventricle.

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So if I looked inside here,
so if I put this probe here,

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that would be my interventricular foramen.

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And the space here

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would actually be filled
with cerebrospinal fluid.

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So I can't see my lateral ventricle here

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because it's behind this membrane.

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We'll look at it in
another brain specimen.

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The lateral ventricles drain
into the third ventricle.

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And I said that the third
ventricle was a great landmark

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for thalamus and hypothalamus.

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And you might remember
that as my mammillary body.

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So anything below my probe

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would be hypothalamus.

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Anything above my probe would be thalamus.

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The third ventricle drains

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through this really
thin cerebral aqueduct.

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And that's a landmark for my midbrain.

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It then drains into this
larger fourth ventricle here

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between my brainstem and my cerebellum.

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And the fourth ventricle is a landmark

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for my pons and my medulla.

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After the CSF flows through here,

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it will go to a big cavity
right behind my cerebellum

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called the cisterna magnum.

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Cistern means vase.

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So it's a really big vase.

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From there, it's going to go

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through my subarachnoid space

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'cause I said that I had fluid
all the way to the outside.

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It's then going to go to
specialized structures

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which we'll see in the blood
supply part of this video

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called arachnoid granulations.

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That will then go into
that venous-filled cavity

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that we talked about,
the dural sinus, right?

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So if I've got all this
fluid going through my brain,

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where is it coming from?

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So if we go back and
look at this model here,

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we see these pink structures.

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And what these pink structures represent

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is a specialized group of
blood vessels and cells

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called choroid plexus.

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Choroid plexus is what produces

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the cerebrospinal fluid.

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It will then travel from
the lateral ventricle

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through the third ventricle,

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through the cerebral aqueduct,

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the fourth ventricle,
to the cisterna magna,

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the subarachnoid space,

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and eventually up to
arachnoid granulations

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that will then take the waste products

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into your venous circulation.

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So this is what the
ventricles look like whole.

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What do the ventricles look like

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when I actually look inside of the brain?

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So this is what your lateral
ventricles look like.

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So this should look very similar to that.

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And if this is,

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these are my two lateral ventricles,

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then this space right here
must be my third ventricle.

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In order for me to find
my fourth ventricle,

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I'd have to be way down in my
brainstem at the cerebellum.

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So we said that this was
the septum pellucidum,

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that we couldn't actually see

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the cavity of the lateral ventricle.

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So let's pull the septum pellucidum back,

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and now you can actually see
the space that would create

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the hole that we see here.

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And more importantly, what you can see now

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is there's this thin structure here

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and I'll pull, try and
pull most of it out.

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This right here is the choroid plexus.

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And what the choroid
plexus is is a collection

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of blood vessels and
specialized ependymal cells

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that are going to secrete
cerebrospinal fluid

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into your ventricular system.

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So cerebrospinal fluid or CSF is one way

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of bringing nutrients to the brain.

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This blood supply tree
or the vascular tree

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is going to be the main
way of supplying blood

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to your brain and brainstem.

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So we're gonna talk about
two types of circulation:

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posterior circulation coming
from my vertebral arteries

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and basilar arteries,

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and another circulation
here coming from my carotid.

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And unlike the vertebrobasilar system

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where you only have one,

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two vertebral arteries come
together to form the basilar.

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We'll see that on a real brain.

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But what I want to point
out is that you have

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an internal carotid for the left,

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and an internal carotid for the right.

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So when you look at the
blood supply to the brain,

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you can see that there is a hemispheric,

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left hemisphere, right hemisphere.

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But the other thing I
want you to focus on is

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that you've got a white
vascular region here

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and an orange vascular region.

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This white vascular
region is going to come

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from the anterior cerebral artery.

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So the more medial

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is anterior cerebral,

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and the more lateral

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is going to be middle cerebral.

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And there's going to be an
itsy bitsy, tiny blood vessel,

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I'm not sure you're
going to be able to see,

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that actually connects
my posterior circulation

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with my anterior circulation.

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So now let's take a look

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at the blood vessels on a real brain.

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This is the basilar artery.

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There is only one.

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Blood coming up comes
into the basilar artery

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from two vertebral arteries.

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Here's one vertebral artery.

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00:14:35,300 --> 00:14:37,550
The other one you can
see is broken off here.

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00:14:38,420 --> 00:14:42,420
So the vertebrobasilar system

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00:14:42,420 --> 00:14:46,460
is responsible for providing all the blood

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00:14:46,460 --> 00:14:49,513
to the entire brainstem and cerebellum.

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00:14:50,440 --> 00:14:52,690
But most importantly,

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00:14:52,690 --> 00:14:57,370
the very last branch
of my vertebral artery

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00:14:57,370 --> 00:15:02,370
is called the posterior cerebral artery.

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00:15:02,930 --> 00:15:06,200
And the posterior cerebral artery

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00:15:06,200 --> 00:15:11,200
goes back here to provide
blood to my occipital lobe.

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00:15:12,090 --> 00:15:14,990
So if you have a stroke

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00:15:14,990 --> 00:15:19,070
in the vertebrobasilar system,

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00:15:19,070 --> 00:15:21,330
you could either have clinical deficits

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00:15:21,330 --> 00:15:25,290
in your brainstem, cerebellum,

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00:15:25,290 --> 00:15:30,290
or visual deficits from
lack of blood supply

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00:15:30,300 --> 00:15:31,683
to your occipital lobe.

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00:15:32,710 --> 00:15:35,350
That's my posterior circulation.

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00:15:35,350 --> 00:15:38,810
My anterior circulation is going to come

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00:15:38,810 --> 00:15:41,070
from my carotid artery.

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00:15:41,070 --> 00:15:44,030
So there is my carotid artery

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00:15:44,030 --> 00:15:47,370
for the right hemisphere.

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00:15:47,370 --> 00:15:50,450
And here is my carotid artery

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00:15:51,510 --> 00:15:53,970
for the left hemisphere.

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00:15:53,970 --> 00:15:57,670
Notice you have one carotid
for each hemisphere,

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00:15:57,670 --> 00:16:00,660
and that there are two major vessels

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00:16:00,660 --> 00:16:04,060
that come off the carotid artery.

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00:16:04,060 --> 00:16:08,010
One is going to be the anterior cerebral.

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00:16:08,010 --> 00:16:10,460
And the anterior cerebral runs

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00:16:10,460 --> 00:16:13,900
right down the interhemispheric fissure.

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00:16:13,900 --> 00:16:17,440
And that's why the
anterior cerebral artery

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00:16:17,440 --> 00:16:19,810
basically supplies blood

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00:16:19,810 --> 00:16:24,810
to only the medial
aspects of your cerebrum.

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00:16:24,870 --> 00:16:27,880
And when I told you about the homunculus,

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00:16:27,880 --> 00:16:32,380
I said that the medial
aspect of my homunculus

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00:16:32,380 --> 00:16:36,890
was essentially my leg and
a little bit of my trunk.

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00:16:36,890 --> 00:16:41,280
So now we've learned that
this more medial artery

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00:16:41,280 --> 00:16:44,470
called the anterior cerebral

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00:16:44,470 --> 00:16:49,090
only provides blood to the
middle part of the cerebrum,

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00:16:49,090 --> 00:16:51,990
including the leg and trunk.

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00:16:51,990 --> 00:16:56,160
The other artery that
comes off of the carotid

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00:16:56,160 --> 00:16:58,670
actually goes deep down here

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00:16:58,670 --> 00:17:03,510
between my temporal and
frontal and parietal lobes.

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00:17:03,510 --> 00:17:07,270
So what it's going to do is
it's going to come out here.

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00:17:07,270 --> 00:17:11,350
This is part of my middle cerebral artery,

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00:17:11,350 --> 00:17:13,730
and it is going to provide blood

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00:17:13,730 --> 00:17:18,070
for the overwhelming
majority of my cerebrum.

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00:17:18,070 --> 00:17:22,660
It's going to be responsible
for receiving sensory

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00:17:22,660 --> 00:17:25,230
and sending motor information

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00:17:25,230 --> 00:17:28,750
to the arms and the face.

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00:17:28,750 --> 00:17:32,100
So if you have a stroke, you want to test,

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00:17:32,100 --> 00:17:35,660
you want to act fast by testing

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00:17:35,660 --> 00:17:39,370
the face, the arms, speech,

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00:17:39,370 --> 00:17:42,800
because both Broca's
area and Wernicke's area

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00:17:42,800 --> 00:17:45,490
are going to be in this territory.

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00:17:45,490 --> 00:17:48,190
So let's take a look and see again,

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00:17:48,190 --> 00:17:52,773
how my common carotid artery here,

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00:17:53,670 --> 00:17:58,670
my common carotid artery
here gives rise to a branch,

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00:17:59,670 --> 00:18:01,810
the anterior cerebral.

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00:18:01,810 --> 00:18:04,070
And the anterior cerebral runs

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00:18:04,070 --> 00:18:07,700
right down the medial part of my brain.

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00:18:07,700 --> 00:18:10,610
And the other branch it gives rise to is

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00:18:10,610 --> 00:18:12,620
the middle cerebral artery.

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00:18:12,620 --> 00:18:16,240
And the middle cerebral artery
is going to provide blood

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00:18:16,240 --> 00:18:19,593
to the vast majority of the cerebrum.

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00:18:20,730 --> 00:18:24,920
The posterior cerebral artery
that does my occipital lobe

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00:18:24,920 --> 00:18:28,900
and a little bit of the inferior
part of my temporal lobe

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00:18:28,900 --> 00:18:32,773
is actually coming from
the vertebrobasilar system.

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00:18:33,670 --> 00:18:36,030
Now, I said there was a way

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00:18:36,030 --> 00:18:39,670
that the anterior and
the posterior circulation

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00:18:39,670 --> 00:18:42,420
was able to come together.

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00:18:42,420 --> 00:18:46,150
And there is one really,
really small blood vessel

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00:18:50,990 --> 00:18:55,490
that connects the anterior
and posterior circulation.

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00:18:55,490 --> 00:18:57,440
And in class, we're going to talk

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00:18:57,440 --> 00:19:00,540
about how this creates a little circuit

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00:19:00,540 --> 00:19:02,750
so that if you have a blood clot,

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00:19:02,750 --> 00:19:05,490
you can actually reroute the blood

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00:19:05,490 --> 00:19:08,720
around this closed circuit.

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00:19:08,720 --> 00:19:13,240
We talked about blood flowing
through the vascular tree,

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00:19:13,240 --> 00:19:17,170
and there being a rerouting system

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00:19:17,170 --> 00:19:19,570
to get blood around some clots.

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00:19:19,570 --> 00:19:23,410
But unfortunately, if you
have a stroke in your brain,

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00:19:23,410 --> 00:19:27,270
you might not be able to reroute around.

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00:19:27,270 --> 00:19:31,650
So stroke, or sometimes people
will call it a brain attack

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00:19:31,650 --> 00:19:34,560
because it's kind of like a heart attack,

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00:19:34,560 --> 00:19:36,580
comes in two varieties:

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00:19:36,580 --> 00:19:40,200
ischemic strokes and hemorrhagic strokes.

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00:19:40,200 --> 00:19:41,550
In an ischemic stroke,

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00:19:41,550 --> 00:19:45,440
what happens is basically
a clot most often

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00:19:45,440 --> 00:19:49,970
or narrowing of the artery
ends up reducing blood flow.

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00:19:49,970 --> 00:19:53,310
And if you don't have blood
flow, you have a lack of oxygen

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00:19:53,310 --> 00:19:56,350
and you have a lack of glucose.

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00:19:56,350 --> 00:19:59,980
So what ends up happening
is the neural tissue dies.

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00:19:59,980 --> 00:20:04,660
And here is an example of
where somebody had a stroke,

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00:20:04,660 --> 00:20:06,930
and this is the area

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00:20:06,930 --> 00:20:09,770
where all the neural tissue died

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00:20:09,770 --> 00:20:14,770
from a lack of oxygen and glucose.

354
00:20:14,890 --> 00:20:16,980
And this is in the most common area

355
00:20:16,980 --> 00:20:20,310
'cause I said out here more laterally,

356
00:20:20,310 --> 00:20:22,610
more laterally, it was going to be

357
00:20:22,610 --> 00:20:24,363
the middle cerebral artery.

358
00:20:26,040 --> 00:20:30,610
Because it's in an area
that isn't high functioning,

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00:20:30,610 --> 00:20:33,800
it's an association cortical area,

360
00:20:33,800 --> 00:20:35,820
this person probably didn't show

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00:20:35,820 --> 00:20:39,220
any clinical signs or deficits

362
00:20:39,220 --> 00:20:44,220
until it started impinging in
areas like Wernicke's area,

363
00:20:44,500 --> 00:20:47,430
the receptive component of speech.

364
00:20:47,430 --> 00:20:50,440
Here's another person that had a stroke.

365
00:20:50,440 --> 00:20:53,677
And again, this would
be an ischemic stroke,

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00:20:53,677 --> 00:20:56,960
and this is all the area of tissue

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00:20:56,960 --> 00:21:00,040
that died from a lack of blood supply.

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00:21:00,040 --> 00:21:01,390
And unlike the last brain,

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00:21:01,390 --> 00:21:06,160
you can see that this brain
is in the more medial aspect.

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00:21:06,160 --> 00:21:08,600
So this would have been due to a stroke

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00:21:08,600 --> 00:21:12,260
to the anterior cerebral artery.

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00:21:12,260 --> 00:21:17,260
Now sometimes you can have
more profound ischemic events,

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00:21:17,410 --> 00:21:21,670
and these more profound ischemic
events can actually result

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00:21:21,670 --> 00:21:26,020
in the loss of tissue in multiple areas.

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00:21:26,020 --> 00:21:28,420
And I think this gives you an idea

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00:21:28,420 --> 00:21:31,580
that the brain has an amazing ability,

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00:21:31,580 --> 00:21:34,570
a sense of what we call plasticity,

378
00:21:34,570 --> 00:21:38,420
to be able for other surrounding areas

379
00:21:38,420 --> 00:21:43,420
to be able to take over the
function of these neurons

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00:21:43,420 --> 00:21:46,510
so that you don't have a clinical deficit

381
00:21:46,510 --> 00:21:51,510
until you lose so much more of your brain.

382
00:21:52,110 --> 00:21:56,450
Now here's three brains
that had ischemic events.

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00:21:56,450 --> 00:21:58,860
The fourth brain I want to show you

384
00:21:58,860 --> 00:22:01,217
is the second type of stroke.

385
00:22:01,217 --> 00:22:05,720
And the second type of stroke
is a hemorrhagic stroke.

386
00:22:05,720 --> 00:22:10,050
This is where you actually
ruptured a blood vessel

387
00:22:10,050 --> 00:22:12,780
and bled into the brain.

388
00:22:12,780 --> 00:22:15,500
Ischemic strokes, if they're caught early,

389
00:22:15,500 --> 00:22:19,460
you can give clot-busting
drugs, kind of like Drano,

390
00:22:19,460 --> 00:22:23,110
and break open the clot and give blood.

391
00:22:23,110 --> 00:22:25,680
But unfortunately, there's no way

392
00:22:25,680 --> 00:22:28,777
of controlling the
bleeding inside the brain.

393
00:22:28,777 --> 00:22:32,423
And this largely is why this person died.

394
00:22:33,300 --> 00:22:36,270
So now, instead of talking
about what could happen

395
00:22:36,270 --> 00:22:39,840
in terms of strokes to the vascular tree,

396
00:22:39,840 --> 00:22:43,830
now we need to consider
not the internal vessels,

397
00:22:43,830 --> 00:22:46,570
but some of these more superficial vessels

398
00:22:46,570 --> 00:22:49,150
that are associated with the brain.

399
00:22:49,150 --> 00:22:53,670
Now, I said that the cerebrospinal fluid

400
00:22:53,670 --> 00:22:55,650
would eventually drain

401
00:22:55,650 --> 00:22:59,910
through something called
an arachnoid granulation,

402
00:22:59,910 --> 00:23:03,630
and that these arachnoid
granulations would then go

403
00:23:03,630 --> 00:23:06,410
through venous structures.

404
00:23:06,410 --> 00:23:08,283
And we've got here,

405
00:23:10,490 --> 00:23:12,020
if I pull the dura back,

406
00:23:12,020 --> 00:23:16,250
you can see these veins
that are being pulled,

407
00:23:16,250 --> 00:23:18,510
and that these veins will go

408
00:23:18,510 --> 00:23:21,890
into what's called a sinus.

409
00:23:21,890 --> 00:23:25,460
So right running right
down the middle here

410
00:23:25,460 --> 00:23:28,640
is going to be a venous-filled cavity

411
00:23:28,640 --> 00:23:30,420
called the dural sinus.

412
00:23:30,420 --> 00:23:32,170
And from the dural sinus,

413
00:23:32,170 --> 00:23:35,550
it'll go into the jugular
vein and back to the heart.

414
00:23:35,550 --> 00:23:39,150
Now, if somebody falls, if
somebody hits their head

415
00:23:39,150 --> 00:23:41,520
and their brain bounces too much

416
00:23:41,520 --> 00:23:45,100
and they end up damaging
these bridging veins,

417
00:23:45,100 --> 00:23:46,510
what they could have

418
00:23:46,510 --> 00:23:49,353
is called a subdural hematoma.

419
00:23:51,190 --> 00:23:54,260
It's like a bruise that
you might get in your body,

420
00:23:54,260 --> 00:23:57,640
but it is a bruise on the brain.

421
00:23:57,640 --> 00:24:01,350
A subdural hematoma isn't that bad

422
00:24:01,350 --> 00:24:06,350
because it's low pressure venous blood

423
00:24:06,430 --> 00:24:09,560
returning back to the heart.

424
00:24:09,560 --> 00:24:13,490
This is opposed to another type of damage

425
00:24:13,490 --> 00:24:15,020
that you could get.

426
00:24:15,020 --> 00:24:19,280
And in this case, this is
a subarachnoid hemorrhage,

427
00:24:19,280 --> 00:24:24,280
under the arachnoid in that
space that has your CSF.

428
00:24:24,430 --> 00:24:27,530
And because the subarachnoid space

429
00:24:27,530 --> 00:24:30,840
has arteries and arterioles,

430
00:24:30,840 --> 00:24:33,880
this is going to be high pressure blood

431
00:24:33,880 --> 00:24:36,980
coming from your heart to your brain.

432
00:24:36,980 --> 00:24:41,790
Somebody that has a subarachnoid
hemorrhage like this,

433
00:24:41,790 --> 00:24:44,990
or like this is going to describe it

434
00:24:44,990 --> 00:24:49,180
as the most excruciating
headache of my life.

435
00:24:49,180 --> 00:24:52,410
And chances are even
before they can make it

436
00:24:52,410 --> 00:24:54,420
to the emergency department,

437
00:24:54,420 --> 00:24:56,130
they will bleed out

438
00:24:56,130 --> 00:25:00,723
because this is high
pressure arterial blood.