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Current time:0:00Total duration:11:28

Video transcript

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 so 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 brainstem now in terms of vessels in terms of blood vessels all 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 gets a little bit tricky here this is the basilar artery this here is the middle cerebral artery I'll call 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 down store 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 one 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 that happens there's two major consequences first because you're leaking blood out of your cerebral circulation these downstream parts of of say your anterior cerebral artery here obviously won't be getting any blood so again this downstream brain tissue is going to 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 a 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 going to 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 not getting proper blood supply and they're not getting enough glucose and they need glucose in your blood stream to to function properly to carry out their complicated functions so what do you think might happen if if a part of your brain just sort of stopped working started to malfunction well intuitively you 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 going to be able to get through the MCA right here's blood in the MCA all of a sudden we're going to lose the abilities that the downstream parts of the brain perform at least temporarily now the middle cerebral artery is 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 Verna Key's area depending on if you want to use the true german pronunciation and these two areas are really really important in determining your speech determining how you speak and 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 going to 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 brainstem well there's a lot of special nerves called cranial nerves that originate on your brainstem 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 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 we blood vessels are involved for example if you get a big clot right about here then you're not going to 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 you alive your brain stem has all of the regulatory centers that control your breathing and your 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 or 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 would 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 want to have it in your brainstem 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 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 buildup of sort of this fatty cholesterol plaque in the walls of your arteries so let's say that you got some cholesterol buildup in the all of the artery here and the internal carotid well as you can imagine blood is going to 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 tube and if you actually have one you're likely to have another so you might have one there and you might have one day here you might have one there so they're really really dangerous atherosclerosis now let me switch gears for a second and talk about something called a TI a or a transient ischemic attack also known as a mini stroke a TI is essentially a temporary interruption of blood flow to to a part of the brain so the symptoms the symptoms of a TI a and a stroke they're really similar but the difference is that a TI a doesn't actually destroy brain cells and it doesn't cause permanent disability so one of the key differences is that a TI a 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 ti a 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 certainly involved in some causes of stroke but strictly speaking strokes or 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 two-thirds of strokes happen in the elderly and people older than 65 a pretty significant 1/3 happening 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