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Studying for a test? Prepare with these 2 lessons on Nervous system diseases.
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Video transcript
- [Voiceover] Here we have the brain of someone who's suffering from multiple sclerosis. You'll notice that there are these bright spots that are found located throughout the brain, known as plaques. These plaques are also referred to as lesions. A lesion is really just a piece of damaged tissue. Now, note how these plaques are forming in different parts of the brain, so the really important thing to keep in mind, is that different parts of the brain will be responsible for different functions. Some parts may be involved in vision, movement, touch, cognition, and even emotion, so you can get a dysfunction in each of these categories, depending on where the lesion formed. For example, if you have a lesion that forms in parts that are responsible for vision, or for seeing, then you won't really be able to see as well. As it turns out, visual symptoms are actually among the first symptoms that people usually experience in MS, so I'm gonna be talking about those first. I'm gonna show you here a picture of the eye. At the back of the eye, you have this structure over here, called the optic nerve. The optic really just carries all the visual information picked up from the eye, to the rest of the brain. As it turns out, it's actually a pretty common site for lesion formation, so let's say we have a lesion that, you know, maybe it forms around here. If you get lesions in the optic nerve, then you can imagine that there will be a lot of problems with the vision. It's not as severe as total blindness, but, in general, your vision is impaired. Let's say you go to the eye doctor. They're gonna ask you to read off a series of letters on a screen, across the board. Your ability to read off of the smallest letters will be pretty badly impaired. You won't really be able to see these letters as well anymore. In addition to that, colors also appear a little bit washed out, so, let's say, you have normal, healthy color vision. You're looking at this green box and it looks like this, but, if you have multiple sclerosis, the green box may actually look a little bit more washed out, so, maybe, something like this. It's not as clear, or not as distinct, I should say. In addition to this impaired vision and this washed-out color vision, people will also just experience general pain, cuz whenever they move their eyes around, it kinda hurts a little bit. Those are some of the major visual symptoms that people feel when they get lesions in the optic nerve, but there are other parts of the brain where, if you get lesions there, then people may experience other visual problems as well. I have this green nerve coming out from somewhere, and it's innervating the muscles of the eye, so this nerve will be responsible for moving the eye around. Where does that nerve come from? It comes from a part of the brain known as the brain stem. Really, there are more nerves that come out, but this is just to simplify our understanding of it. Now, in the brain stem, you have these cell bodies. These cell bodies are gonna project their axons into these nerves, then these nerves will, ultimately, innervate the muscles of the eye. As it turns out, this is actually a pretty common site of lesion formation, this general area of the brain stem, or, at least, where the axons are in that region of the brain stem, so you can imagine that you'll get a lot of problems with moving your eye around. If you ever look at the eyes of a person with MS, what you'll notice is that they look like they're vibrating a little bit, so, sometimes, they may have a vibration motion horizontally, or, even vertically, as well. In addition to that, if you show a yellow bar of light maybe, it could be any image, but let's say we have a yellow bar of light, if you show this, they may report seeing kind of a second yellow bar of light right next to it, so they're experiencing this double-vision effect. The reason is because, well, their eyes aren't really moving in unison anymore. Because they're not moving in a coordinated fashion, they're not really able to converge those images that they receive, so, because of that, you see this double-vision, you see two of one object. The brain stem isn't really just gonna innervate the eye, it can innervate other parts of the body as well. Let me clear up some space here. As it turns out, the brain stem also is gonna innervate a part of the body, something known as your throat. You have a whole bunch of muscles in your throat, and the muscles in your throat are gonna be doing a whole bunch of different things. Some really important functions would just be talking and swallowing food, so if you get lesions in the brain stem, maybe you have some lesions that form over here, then you can have problems doing just that. A lot of people with MS, maybe they may stutter a little bit, they may not really talk as well as they used to. They may also have difficulty in swallowing their food. It becomes much more painful and much more difficult to do just that. Now, I wanna show you symptoms that are associated with lesions in another part of the central nervous system. Let me actually just clear up a little bit of space here again. Now, I'm showing you the picture of a brain of someone who's kinda facing towards you. Down here, we have a picture of the spinal cord, and this is really just a segment of that spinal cord. The spinal cord is gonna be responsible for connecting the brain with the rest of the body, so it transmits information about both touch and motor control between the brain and the rest of the body. Let's say you have some kind of nerve fiber ending over here. This nerve fiber ending is, basically, gonna transmit the information about touch to the spinal cord. Then, from the spinal cord, that information is just gonna be taken up to the rest of the brain, so, maybe, you have some more nerves that go up from the spinal cord, and, then, into the brain. Then here, it's just later processed. Of course, this is a very simplified schematic, but, in general, if you get lesions in this area, maybe you get some kind of lesion over here, or maybe one over here, then you can get a lot of problems with touch. One pretty common symptom that people might feel is numbness. In addition to that, people may have the sensation of pins and needles prickling into their skin. This is really just the equivalent of your limbs falling asleep. We typically call this paresthesia. Finally, people may just experience plain old pain. cuz sometimes if you look down or you look forward, then the person may kinda feel the sensation of like an electric shock, moving down their spinal cord, then radiating into the rest of their limbs, so it's not just touch information that's transmitted between the body and the brain, it's also motor information. Motor information can move down from the brain into the spinal cord. Then, from the spinal cord, that information can contact another set of nerves that'll innervate the muscles of your hand. If you get lesions in these areas, you're gonna get some problems with motor control. For example, a lot of people may experience paralysis. They may not be able to use their legs to move around, so that renders a lot of people incapable of walking, so they need to use wheelchairs and canes to move around. On the flip side of paralysis, they may experience spasticity. In spasticity, their muscles are too stiff, they're too overactive, and, because they're too stiff, they become very tense. It's as if the muscles are just constantly contracting for some reason, and because they're constantly contracting, this can lead to quite a bit of pain in those muscles. In addition to that, people may also experience problems with bladder and bowel controls. Maybe they're urinating too frequently or maybe they're finding difficulty in urinating where there's a problem in the control of the bladder, and there's also a problem with the control of the bowel movements. Then, finally, people may experience sexual dysfunction. Oftentimes, a lot of people will have problems in initiating or maintaining arousal. They may also have problems in achieving an orgasm. Next, let's turn this brain around and let's talk a little bit more about some of the cognitive symptoms that people experience in MS. Now our brain is kinda looking to the right, and you'll see that I've already shaded in a part of the brain, and this part of the brain is simply known as the frontal lobe. What does the frontal lobe do? Well, it's responsible for cognition. What are some cognitive behaviors? Well, there's attention, working memory, thinking, and decision making. If you get lesions in the frontal lobe, then you can experience a lot of problems in all these cognitive functions. For example, a lot of people may experience problems with paying attention to things. They may also be a little bit more forgetful. They may have problems thinking about and understanding certain concepts, and, subsequently, their ability to solve problems is pretty heavily impaired. Finally, they may also be a little bit indecisive as well.