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Current time:0:00Total duration:6:45

The vestibular system, balance, and dizziness

Video transcript

if I asked you to list your census you would probably mention things like sight or sound or taste but it turns out that we can actually detect a lot more than that one sense that's really important but not often thought about is our vestibular system which is a system that is very important for our sense of balance and spatial orientation and while a lot of information about balance and body position is gained through receptors in our bodies that let us know our limbs are in space it actually turns out that a lot of our sense of balance and spatial awareness comes from receptors in our inner ear so let's take a moment to focus on our auditory system and what I want to do is focus on the inner ear the part here that's shaded in orange and to get a better idea of what that part looks like I've pre-drawn an enlarged version and if you're familiar with the auditory system part of this will probably look familiar to you in particular you might be familiar with this spirally snail shaped structure here which is referred to as the cochlea and this is the portion of your inner ear that's full of specialized auditory receptors that process sound and then transfer information about it to our brain but what I want to focus on now are these loops on the other side which we refer to as semicircular canals so we have this anterior canal a posterior canal and then this lateral canal which is also sometimes referred to as the horizontal canal and it can be kind of hard to see this 3d structure on a 2d image but these canals are actually all orthogonal to each other meaning that they are all at right angles to each other let me draw some faces here to try to make this a bit clearer so I'm going to draw some axes on this head to try to orient us so imagine a line that's going from our nose to the back of our head and we're going to label that the x axis and now imagine another line that's going from our left ear to our right year and we're going to label that one the y axis and here let me let me add the x axis to this top picture and the Y access to the bottom and I've put these as dotted lines to signify that they're actually coming directly out of the screen towards us in addition to the x and y axes though we also have the Zia excess and that one goes straight up and down so you can see it on both images here and each of our semicircular canals actually lines up with one of these axes each of these canals is filled with a fluid that's known as endo lymph and when we rotate along a certain plane it causes the endolymph to shift within that particular semicircular canal and this allows us to sense what plane our head is rotating along but because we're also sensitive to how much of the fluid is moving and how quickly we also can get information about the strength of the rotation another part of our inner ear that gives us information relating to balance and spatial orientation are the i/o lithic organs let me write that here and the autolytic organs include the utricle and the saccule which i've labeled here and they help us to detect linear acceleration and head positioning and within these structures are crystals actual calcium carbonate crystals that are attached to hair cells within kind of a viscous gel substance and if we accelerate in a direction or say move from standing up to lying down this causes the crystals to move because they are heavier than the surrounding gel environment and when they move they physically pull on the hair cells that they're attached to which is what triggers an action potential that carries this information to the brain so let me try to draw this so you can get a clearer picture of what it looks like I'm going to erase my two faces here and let me change my pen color all right so we have a person standing here and within their ear within their auto lithic organs our hair cells and those hair cells are attached to crystals let me draw another hair cell next to it and when we're just standing up gravity is pushing those crystals in one direction namely straight down let's think about what would happen if we lay down so now we have a person in he's lying down he's all ready to go to sleep and now because he's changed his orientation these crystals are going to shift in their position because of course gravity is still pointing in the same direction and as they do this they pull the hair cells along with them and I just find this to be real be fascinating I mean think about this you have crystals in your ear that are physically pulled in different directions by acceleration and gravity that allow you to detect head positioning your crystals that respond to gravity and this is real this is actually something and is going on in your head right as we speak and I think this is just one of the coolest sense organs that we have so you've experienced what happens when the vestibular system works but you've probably also experienced what happens when it goes wrong because this results in things like a dizziness and vertigo so let's think about how this might work and let's think back to the semicircular canals as we spin the fluid within them the endolymph moves along the direction that we're turning but this liquid doesn't always stop spinning right when we do and this is especially true if we're spinning vigorously or for long periods of time and think about what the result of this might be so you have stop moving but the continued movement of the endolymph is resulting in signals being sent to your brain that indicate that you are still moving even after you have stopped and this results in the experience of dizziness and when the fluid eventually stops moving is when the dizziness subsides and interestingly knowing this also helps us figure out how we can combat dizziness rotating in the opposite direction of how you were originally spinning encourages the movement of the endo lymph in that opposite direction and this can help stop the continued motion of the endolymph in the original direction by kind of cancelling it out that's not the only thing that causes dizziness though remember that one of the ways that we get information about body position is by sensing the orientation of crystals in our auto lithic organs with respect to gravity if you are in a situation without gravity let's say if you were an astronaut your automatic organs probably wouldn't work very well because gravity won't pull down on them in the same way and because of this concepts like up and down kind of become meaningless and apparently this can be really disorienting and this is also one of the dangers of scuba diving buoyancy can have the same effect as gravity and this can sometimes result in divers becoming really disoriented when they're underwater and this is especially the case when they don't have visual cues about which way is up or which way is down