Judul : California School Of Health Sciences
link : California School Of Health Sciences
California School Of Health Sciences
- [voiceover] so beforewe sort of jump into what strokes are, let mejust 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 thecontents of their skull.
California School Of Health Sciences, so let's do some labeling here. we've got the skull here, and obviously, the skullprotects 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 seehere, these are all veins. these are veins that drain the brain. and now let's label some arteries. so here in front, we havethe internal carotid artery. and remember, we're onlylooking at the left side here.
so we can only see the left one. and here, sort of runningup 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 theposterior 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 seethe 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 todisturb 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 cerebralartery 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 bloodfor its oxygen needs, that brain tissue wouldstart to get injured
and start to die off. and the second kind of disturbance, once that's not as common, butstill 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, thataneurysm 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'stwo 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 thetwo types of stroke. you can get stoppage ofblood flow to an area, which is also called an ischemic stroke, "ischemic" referring to an environment, the cellular environment wherethere's not enough oxygen, or you can get this rupture ofa vessel that we saw earlier. and that's also called ahemorrhagic stroke. hemorrhagic. and "hemorrhagic" refers to, sort of, a sudden torrential bleeding outburst.
so, ischemic strokeand hemorrhagic stroke. but regardless of whetheryou have an ischemic stroke or a hemorrhagic stroke, either way your brain cells aregonna start to malfunction after about three minutes or so. and that's because they havenow a lack of oxygen, right? because they're notgetting 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 justsort of stopped working, started to malfunction? well, intuitively, youmight start to think, "well, hey, if a part of mybrain starts malfunctioning, "i might lose those abilities
"that that part of thebrain 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 inthe middle cerebral artery. well, if we get a clot here, then that means thatblood isn't gonna be able to get through the mca, right? here's blood in the mca.
all of a sudden, we'regonna lose the abilities that the downstream partsof the brain perform, at least temporarily. now, the middle cerebralartery's pretty important. it actually supplies blood to two really importantareas of the brain, one called broca's area, onthe outside of the brain, and one called wernicke'sarea, or wernicke's area, depending on if you wanna
use the true german pronunciation. and these two areas arereally, really important in determining your speech, determining how youspeak and whether or not you can understand whatpeople are saying to you. so if you get a big clot inyour middle cerebral artery, and you happen to stopblood 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 comingoff the basilar artery. right? so that runs up your brain stem. well, there's a lot of special nerves called cranial nerves thatoriginate on your brain stem and sort of go theirseparate 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 eyelidsmight start to droop, basically, you might not be able to use some of the muscles of your face. so what exactly determineshow bad a stroke is? well, two things: wherein the brain it happens, and how much brain tissueis actually damaged.
and what determines that? well, that's determined by whichblood vessels are involved. for example, if you get abig clot right about here, then you're not gonna allowblood to your brain stem. so your brain stem would start to die off, and that would be really, really bad because your brain stemis really responsible for keeping your alive. your brain stem has allof 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 littlevessel right about there, on in this one here, then how much brain injurywould you end up with? well, you'd end up with alittle in each small area. and while, ideally, youdon't have any brain injury,
the sort of functionaldisability that you'd suffer if you had these small strokes, compared to this really, reallybig and significant stroke, there'd be a pretty big difference there. so just to reiterate, theseverity of the stroke depends on where you getyour stroke, right ... so again, you don't wannahave 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 somecommon heart conditions, like atrial fibrillation,where the uppermost chambers of your heartdon'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 walland 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 somethingcalled atherosclerosis, or build-up of, sort of,this fatty cholesterol plaque in the walls of your arteries. so let's say that you gotsome cholesterol build-up in the wall of the arteryhere, in the internal carotid.
well, as you can imagine, blood is gonna have areally, really hard time getting past this, sortof, massive cholesterol that's stuck in the wallof the artery, right, this atherosclerosis. and these can happen in multipleplaces 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 atemporary interruption
of blood flow to a part of the brain. so the symptoms, the symptomsof the tia and the stroke, they're really similar. but the difference is thata tia doesn't actually destroy brain cells and it doesn't cause permanent disability. so one of the key differencesis 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 functionagain for weeks or months, or maybe even for the rest of your life. so let me just quickly showyou what this would look like. so in a proper stroke, let'ssay this vessel gets blocked. without treatment, thistissue will die off. but in a tia, you'd get a little clot, this area would start to become injured, and then the clot wouldsort of spontaneously
break up and go away. and then, all of asudden, this brain tissue would start to go back to normal again. and so, in the vastmajority of situations, you won't be left with anypermanent 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, theheart's certainly involved in some causes of stroke. but strictly speaking,strokes are conditions related to a mismatch between cerebral bloodflow 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 thatabout 2/3s of strokes
happen in the elderly,and people older than 65, a pretty significant 1/3happen in people under 65. so strokes can happen inpeople 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 controllingany high blood pressure or stopping smoking.
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