- [Voiceover] So before we sort of jump into
what strokes are, let me just sort of orient you
to this, to what we're looking at here.
So this is a side view of a person.
And we can see the contents of their skull.
So let's do some labeling here.
We've got the skull here,
and obviously, the skull protects the brain.
We have the cerebrum, the most obvious
part of the brain, in pink.
We have the cerebellum down here,
and we have the brain stem.
Now, in terms of vessels, in terms of blood vessels,
all of the blue that you see here, these are all veins.
These are veins that drain the brain.
And now let's label some arteries.
So here in front, we have the internal carotid artery.
And remember, we're only looking at the left side here.
So we can only see the left one.
And here, sort of running up inside the vertebrae,
we have the vertebral artery.
Now it gets a little bit tricky here.
This is the basilar artery.
This here is the middle cerebral artery.
I'll call it the MCA.
Here we have the posterior cerebral artery.
We'll call that the PCA.
And in front here, we have the ACA,
or the anterior cerebral artery.
And you can sort of see the Circle of Willis
is formed right there.
All right. So let's jump into it.
So all those vessels we just talked about,
that's your blood supply to your brain.
And if you lose some or all
of that blood supply to your brain,
then you lose some or all brain function.
So the loss of some blood supply
causing the loss of brain function,
that's a stroke.
So there's two main ways to disturb this blood supply.
The most common type of disturbance
is where you get stoppage of blood flow
to a part of your brain.
So let me draw this out for you.
Let's say that this bit
of the anterior cerebral artery is blocked off.
This means that blood won't be able to go
from this previous part of the ACA
over to this next part of the ACA.
And if blood can't get through,
then the brain tissue downstream,
that depends on that blood for its oxygen needs,
that brain tissue would start to get injured
and start to die off.
And the second kind of disturbance,
once that's not as common, but still really, really serious,
is where one of the blood vessels
of your cerebral circulation,
where one of the blood vessels ruptures.
Let's say that this bit of the ACA,
right at the junction between the ACA
and the anterior communicating artery,
started to balloon out.
Right? It started to form an aneurysm.
Well, eventually, that aneurysm could rupture.
And if it ruptured, you'd start leaking blood
out of your cerebral circulation
and into the space around your brain.
So if that happens, there's two major consequences.
First, because you're leaking blood
out of your cerebral circulation,
these downstream parts of, say,
your anterior cerebral artery here,
obviously won't be getting any blood.
So again, this downstream brain tissue
is gonna have a lack of oxygen around.
So it'll start to get damaged.
Also, the blood will start to collect
and sort of push on your brain tissue
and cause damage to your brain that way.
So those are really the two types of stroke.
You can get stoppage of blood flow to an area,
which is also called an ischemic stroke,
"ischemic" referring to an environment,
the cellular environment where there's not enough oxygen,
or you can get this rupture of a vessel that we saw earlier.
And that's also called a hemorrhagic stroke. Hemorrhagic.
And "hemorrhagic" refers to, sort of,
a sudden torrential bleeding outburst.
So, ischemic stroke and hemorrhagic stroke.
But regardless of whether you have an ischemic stroke
or a hemorrhagic stroke, either way
your brain cells are gonna start to malfunction
after about three minutes or so.
And that's because they have now a lack of oxygen, right?
Because they're not getting proper blood flow,
not getting proper blood supply,
and they're not getting enough glucose.
And they need glucose in your bloodstream
to function properly, to carry out
their complicated functions.
So what do you think might happen
if a part of your brain just sort of stopped working,
started to malfunction?
Well, intuitively, you might start to think,
"Well, hey, if a part of my brain starts malfunctioning,
"I might lose those abilities
"that that part of the brain performs," right?
So let's look at a few examples here.
So let's say we get a clot.
This is a clot here.
Let's say we get one in the middle cerebral artery.
Well, if we get a clot here,
then that means that blood isn't gonna be able
to get through the MCA, right?
Here's blood in the MCA.
All of a sudden, we're gonna lose the abilities
that the downstream parts of the brain perform,
at least temporarily.
Now, the middle cerebral artery's pretty important.
It actually supplies blood
to two really important areas of the brain,
one called Broca's area, on the outside of the brain,
and one called Wernicke's area, or Wernicke's area,
depending on if you wanna
use the true German pronunciation.
And these two areas are really, really important
in determining your speech,
determining how you speak and whether or not
you can understand what people are saying to you.
So if you get a big clot in your middle cerebral artery,
and you happen to stop blood supply to Broca's area
and/or Wernicke's area, you're gonna end up
with problems with your speech.
Now, let's do another example.
Let's say you get a clot here,
in this little artery coming off the basilar artery.
Right? So that runs up your brain stem.
Well, there's a lot of special nerves
called cranial nerves that originate on your brain stem
and sort of go their separate ways from there.
And some of them are involved
in controlling your facial muscles.
And if these neurons lose oxygen,
it means that you might start to have
the edges of your mouth droop,
it means that your eyelids might start to droop,
basically, you might not be able to use
some of the muscles of your face.
So what exactly determines how bad a stroke is?
Well, two things: where in the brain it happens,
and how much brain tissue is actually damaged.
And what determines that?
Well, that's determined by which blood vessels are involved.
For example, if you get a big clot right about here,
then you're not gonna allow blood to your brain stem.
So your brain stem would start to die off,
and that would be really, really bad
because your brain stem is really responsible
for keeping your alive.
Your brain stem has all of the regulatory centers
that control your breathing and your heart
and a lot of your other vital functions.
In contrast, if you got a clot, let's say,
in this tiny little vessel here,
or in this tiny little vessel right about there,
on in this one here,
then how much brain injury would you end up with?
Well, you'd end up with a little in each small area.
And while, ideally, you don't have any brain injury,
the sort of functional disability that you'd suffer
if you had these small strokes,
compared to this really, really big and significant stroke,
there'd be a pretty big difference there.
So just to reiterate, the severity of the stroke
depends on where you get your stroke, right ...
So again, you don't wanna have it in your brain stem ...
And how much brain area is involved.
And is this brain injury irreversible?
Well, most of the time, yes.
Neurons will start to die
after about four minutes without oxygen.
So what would cause a stroke to happen?
Well, there's some common heart conditions,
like atrial fibrillation, where the uppermost
chambers of your heart don't contract properly.
That often creates blood clots.
And then those blood clots, when they,
when they get pumped out of your heart,
they can travel up to your brain
and get stuck in your brain blood vessels,
like we saw earlier.
Another common heart-related cause
is a myocardial infarct, or a heart attack.
So when you have a heart attack, a part of your heart wall
might start to not contract properly.
So when that happens, little blood clots
can grow on the heart wall and then be pumped out,
up into the brain.
Another really common cause, and actually
one of the most common causes of stroke,
is when you get something called atherosclerosis,
or build-up of, sort of, this fatty cholesterol plaque
in the walls of your arteries.
So let's say that you got some cholesterol build-up
in the wall of the artery here, in the internal carotid.
Well, as you can imagine,
blood is gonna have a really, really hard time
getting past this, sort of, massive cholesterol
that's stuck in the wall of the artery, right,
this atherosclerosis.
And these can happen in multiple places in the brain, too.
And if you actually have one,
you're likely to have another.
So you might have one there,
and you might have one, say, here,
you might have one there.
So they're really, really dangerous,
atherosclerotic plaques.
Now, let me switch gears for a second
and talk about something called a TIA,
or a transient ischemic attack,
also known as a mini-stroke.
A TIA is essentially a temporary interruption
of blood flow to a part of the brain.
So the symptoms, the symptoms of the TIA and the stroke,
they're really similar.
But the difference is that a TIA doesn't actually
destroy brain cells and it
doesn't cause permanent disability.
So one of the key differences is that a TIA will resolve,
it'll kind of go away within 24 hours,
whereas, if you have a stroke,
if you've had a proper stroke,
you may not gain normal function again for weeks or months,
or maybe even for the rest of your life.
So let me just quickly show you what this would look like.
So in a proper stroke, let's say this vessel gets blocked.
Without treatment, this tissue will die off.
But in a TIA, you'd get a little clot,
this area would start to become injured,
and then the clot would sort of spontaneously
break up and go away.
And then, all of a sudden, this brain tissue
would start to go back to normal again.
And so, in the vast majority of situations,
you won't be left with any permanent brain cell death.
So to finish off, let's just clear up
a few misconceptions about stroke.
So there's a common thought
that strokes are primarily heart-related.
And, as we saw earlier, the heart's certainly involved
in some causes of stroke.
But strictly speaking, strokes are conditions
related to a mismatch
between cerebral blood flow supply and demand.
So it's a cerebral, it's a brain problem.
There's another common misconception
that strokes only occur in the elderly.
And while it's true that about 2/3s of strokes
happen in the elderly, and people older than 65,
a pretty significant 1/3 happen in people under 65.
So strokes can happen in people of varying ages.
Last, and probably the most important,
strokes are not unpreventable.
There's a lot of things you can do
to reduce your risk of having a stroke,
such as controlling any high blood pressure
or stopping smoking.