[MUSIC] Okay so the stimulus for the vestibular system is head acceleration. So what does that mean? That means that as I accelerate my head, if I turn my head, there's a moment where I'm accelerating, and then as I hit a constant velosophy, velocity I am no longer exciting my vestibular system. But at that initial acceleration up to a steady velocity, I am accelerating and I am stimulating my vestibular system. So, there are two different types of acceleration. There's linear acceleration, which is the bet, the best example of linear acceleration is the acceleration that goes down towards the core of the earth. That's gravity. It's a law. It always happens. So if you wanted to sense gravity, if you wanted to have some kind of an organ that would sense gravity, what would you choose? Well you'd choose something with a mass. So if I hang this rock, you can see that the, the string is taut and that if, if I go like this, if go like that, it flies up. If I oppose gravity, it can fly up. But if on the other hand, if I put a feather on here, nothing's happening. So a feather's a really bad way to sense gravity, but a rock is a really good way to sense gravity. And we have something that is akin to a rock, it has a heavy mass. It's made of calcium carbonate and it's sitting in our inner ear. Those the, the part of the vestibular system that deals with linear acceleration is called the, are called the otoconial organs, and we'll look at this in another moment. Otoconial organs. Or otoconial masses. So, there's also another type of acceleration, and that's ro, rotational or what we call angular acceleration. So an example of angular acceleration is what occurs on a merry-go-round. You're going around and around. Or if I twirl, that's angular acceleration. I'm accelerating around in, not in a line, but in a circle. And in order to under, in order to measure that angular acceleration, what we need to do is to have, again, some kind of a mass that, that the acceleration can work on. But in this case what we do is. We make an inner tube, there's an, essentially an inner tube in our ear, and it's filled with fluid. And at one point in the inner tube is a, is essentially a feather, a membrane that's very light, that the fluid can act on. So remember that force equals mass times acceleration. And so what we would want to do, is we want to have the force act on this the acceleration act on this mass. Now while the feather is not good to measure gravity, it is, it, it, it does, if you look at this part of the feather, you can see that it moves with friction through the air. And so if the air were instead fluid, it would do the same thing. And that's what this membrane here called the cupola does. It measures the movement, the rotatory movement. Okay, so, bottom line is that we, the vestibular system uses head acceleration to, as, as its stimulus. Head acceleration is the starting stimulus for the vestibular system. In the next segment what we're going to do is we're going to look at a, in a little more detail at these two different parts of the vestibular apparatus. [MUSIC]
