[MUSIC] Okay, so let's just go in a little more detail as to how we collect information about angular and linear acceleration. So, we're looking down on half a skull, the top half has been removed. Up here is the front, back here is the back, and this is the foramen magnum here. And, what I've just drawn is that there's linear acceleration in red, which can take you either forward, to the side, or up and down. And then there's angular acceleration, which has, also has three planes, like this, like this, and like that. So, a plane of, of rotation that's like this, a plane of rotation that's like this, and a plane of rotation that would swing your hea, head around. This plane, by the way, is called the yaw plane. Okay, so how do we sense this? Well, as I said before, we have essentially what is an inner tube. And so, that if we swirl around, the fluid in here swirls around, but the, the bone, the, the, the edge of, of the inner tube doesn't move. So, there's relative motion of the fluid, and we're going to then sense that using hair cells, at, at, at a, at one point in the inner tube. And similarly, there's an, there's an inner tube that is sitting in this plane, and in this plane, going like this, and going like that. And, that allows us to sense, angular acceleration in any plane of, of rotation. So, what does that look like? What we're looking at here, let me actually go back, what we're looking at is a dissected bone that is, that is essentially this part where the top of the inner ear, this, this petrous bone has been removed. And, now we're going to look at it from the side. Okay, so what, so this is the back. This is the front. The ear canal is, is down, down there. And, you can see just one of these semi-circular canals, one of these inner tubes. And in the next slide, you'll see all three. You see one is here, one is here, and one is there. They're all at right angles to each other, and that way we cover all three ro, all three angles of rotation. Very cute trick, very nice, okay? And, the cochlea, just for those of you who are interested, is right about there. Okay, so the semi, let's go over to the board for a minute. The semicircular canals are sensing angular acceleration. There are three of them, and they divide up the three rotational planes. And, when these are not working correctly, what's our perception? Our perception is called vertigo. Vertigo means that either I feel like I'm spinning, so the self is spinning, or that the, one feels that the outside, the world is spinning. So, I can, I can st, be standing here, not moving, and feel as though the room is spinning around me, or that I am spinning. That's called vertigo. Now, the other type of, acceleration we talked about was linear acceleration, and that is [COUGH] handled by the otoconial masses. Which as we go back over here, so here are the three canals. You can see that they all enter into a vestibule, a common vestibule. And there's fluid within all of that, and then in this area there are two otoconial masses. One that's oriented like this, and one that's oriented in this plane. And, the one that's oriented in this plane will detect linear acceleration anywhere in the horizontal plane, in any direction. And, the one that's oriented like this is going to detect changes in grav, in gravity, essentially. So, if I, if I jump off a cliff, my the, the, otoconial mass, there's going to be more acceleration on the otoconial mass going down. If if I jump up, I can oppose gravity, and the otoconial mass will rise up a little bit. So, in that way, I can detect vertical changes in acceleration. I can feel weightless, or feel very heavily weighted, depending on, on, on the conditions. If I went to the moon, for instance, my otoconial mass would not, would, would lift a little bit. The, the gravitational pull of the moon is, is less. Okay. So, what happens, when the otoconial masses don't work? And, this is not uncommon. What we're going to see towards the end is that in, as, as we age, we lose otoconial mass. And so, the mass goes from being more stone like to being more feather like. And, as you may, as we've already said, a feather is not a good detector of gravity. So, as we age we become less able to detect very, just at the stimulus level, we are less able to detect gravity. And, so what does this lead to, dysfunction of, of the otoconial masses? It leads to something called disequilibrium, which is different from vertigo. So, what it means is that as I stand here, I feel like I'm going to fall over, I don't feel like I'm in balance. Even if I were sitting, if I had a,a severe case of disequilibrium, even as a I sat, I would feel like I'm not in balance and I could still fall over. So, that's disequilibrium. Now, I just want to make one final point, dizziness, dizziness is not a clinical term. So, dizziness could mean, some people might use it to mean vertigo, some people might use it to mean de, disequilibrium and some people might use it to mean that they feel light headed. Which is more a cardiac issue, than a, necessarily a neurobiological issue. So, we're talking about two major symptoms here, vertigo and disequilibrium. And, as I mentioned in the very beginning, both of those might be accompanied, or, or often are accompanied, by a feeling of nausea. Vestibular system has a, has an inner road to our, our sense of nausea. Okay, so in the next module, we're going to figure out how we use this structure to produce physiology, to produce sensation and what we do with that sensation. [MUSIC].
