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What is multiple sclerosis?

Visit us (http://www.khanacademy.org/science/healthcare-and-medicine) for health and medicine content or (http://www.khanacademy.org/test-prep/mcat) for MCAT related content. These videos do not provide medical advice and are for informational purposes only. The videos are not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of a qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read or seen in any Khan Academy video. Created by Jaffer Naqvi.

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Video transcript

- [Voiceover] Ok, so let's say you have some kind of letter that you wanna, that you wanna deliver, right? So you have a letter that's in your mailbox, and let's say that this is the sender of the letter, right? And so the sender of that letter is gonna deliver that mail all the way over here to the recipient, right? And the way that they're gonna do that is you're gonna have this mailman in this truck deliver it from the sender to the recipient, and they're gonna drive along this road. But then let's say something happens. Let's say, for some reason, an earthquake happens, right? And the earthquake actually destroys the road over here. And so now, the mailman can't really get to where they need to go anymore, right? Because the road has been damaged. So why am I giving this extremely hypothetical scenario? Well I think that it serves as a pretty good analogy towards understanding a disease called Multiple Sclerosis. So Multiple Sclerosis is a disease of the brain. And more specifically, it affects the communication within the brain. So what do I mean by communication in the brain? Well in the brain, you have all these neurons, right? You have all these neurons that are constantly talking to each other, kinda like these two neurons over here. And so this neuron is going to send an electrical signal down the length of a diaxon. And that electrical signal is in the form of an action potential. And so to improve the efficiency of the communication, you have this stuff that kind of insulates the axon, so, this stuff that I've drawn here in red is called myelin. And it really just makes the action potential move down the axon much more quickly. So we can actually kind of compare this two-way communication system, right, with our mailman. So, you know we have kind of the sender of the message, that would be the first neuron, we have the message, that would be kind of like the action potential, we have the road, which would be, you know, the myelin and the axon together, and we have the recipient. Now, in our analogy, we had an earthquake that actually destroyed the road somehow. So, in Multiple Sclerosis, what happens is, well, you get destruction of the road, and more specifically, you get a degradation of the myelin. And so because there's degradation of the myelin, we can call Multiple Sclerosis a Demyelinating Disease. So this is really where that disruption in the communication goes on, right? And when the myelin is degraded, the action potential won't really travel down the axon as quickly anymore, and sometimes it may not even travel down to begin with. So what's causing that degradation? Well as it turns out, in Multiple Sclerosis, the immune system actually sneaks its way into the brain, and when the immune system sneaks its way into the brain, for some reason it mistakenly recognizes that myelin, right, this myelin over here, as foreign. And when it mistakenly recognizes it as foreign, it starts to attack the myelin, hence this degradation. And because the immune system is attacking the body itself, we call Multiple Sclerosis an Autoimmune Disease as well. So that's kind of a cellular perspective on Multiple Sclerosis, but now I kind of want to give you a more macroscopic perspective on what the disease does to the brain, right? So let me clear up some space over here. And let me actually show you now two different brains. So this is just really a brain scan, or two different brain scans of, well, two different brains. So on the left, we have a perfectly healthy brain. And on the right, we have the brain of someone who's suffering from Multiple Sclerosis. Immediately on the right brain you can tell that you have these bright spots over here, right, called Plaques. So Plaque is also really referred to as a Lesion. And a Lesion is really just a piece of tissue that's been damaged. So let's say, for example, you know, you have a hand over here, you know, maybe you get a cut on your hand somehow. Right, you can call that cut kind of a Lesion of the skin. In Multiple Sclerosis you have a Lesion in the brain, right? And those Lesions are really coming from the damaged myelin from the immune system. So what happens is, you have all these immune cells that kind of come together, right, they kind of cluster around certain parts of the brain, and they attack it. And when you have a whole bunch of immune cells coming together to attack a certain part of the body, we call this Inflammation, and because it's happening in the brain, we call it Neuroinflammation. Now, the condition in which you have these Lesions, in the brain, is called Sclerosis. In the case of Multiple Sclerosis, you have multiple Lesions hence why we call it Multiple Sclerosis. Now notice how you're getting these Lesions in different parts of the brain, ok. Different parts of the brain are gonna be responsible for different functions. Some may be responsible for Vision, others may be responsible for Cognition, for moving around, for Movement, for Touch, and so on and so forth. And depending on where these Lesions form in the brain, you can get a variety of different symptoms that can affect all of these functions. Now, why do these Lesions form? Why does the immune system attack the brain? The problem is that we don't actually know. We're not really sure with 100% certainty what causes Multiple Sclerosis. All we know is that some people may have a kind of Genetic Predisposition towards developing the disease, and that there are also probably some Environmental Factors that may be involved as well. And the fact of the matter is that your genetics can really interact with the environment, and that can kinda stimulate the progression of the disease. Now the exact types of genes that are involved, and the exact types of Environmental Factors that may be involved will be a talk that I'll cover in a later video, but for now this is really all that we know about the causes of Multiple Sclerosis. Now even though we don't really know perfectly what causes Multiple Sclerosis, we do know who is more likely to develop the disease. So I'm gonna actually clear up some more space here again. And so now I'm gonna show you a picture of the earth. And the reason is because I wanna give you a global perspective on, you know, the prevalence, and the incidence of Multiple Sclerosis. So the disease affects about 2.5 million people worldwide. Now, is everyone on the planet equally likely to develop the disease? Well, no. As it turns out, if you move north from the equator, right, so if you move north from here, you'll notice that the incidence of MS actually increases. And the incidence is actually pretty high, you know, in these northern areas, right, so here in Canada, and in the northern United States, and here in a lot of Europe and Russia as well. So it often affects Caucasians more than other races. And more specifically among the Caucasians, it affects people of Northern European Descent more often. The disease is also more common in women than it is in men. Right, and it's thought that of the 2.5 million people worldwide about two thirds of them are women. So 66% of them are women. So what age do people start to develop MS? It's usually in the age range of 20 to 50 years old. And it's usually on the earlier end of that spectrum. And lastly, one thing that I really want to emphasize is that the disease itself is NOT FATAL. So the disease itself won't actually kill you, right, but the Life expectancy is a bit lower. And it's thought to be lowered by about, you know, a few months to a few years. Now even though it's not fatal, the disease itself is quite debilitating, and it can really affect the person's lifestyle through a number of different signs and symptoms, and that'll be a topic that I'll cover in the next video.