 And this is where we're going to start to talk about equilibrium. So equilibrium sensations, they're provided by what's called the vestibular complex, which can be broken down into the saccule and utricle in the vestibule, which they're responsible for like linear acceleration and the impact of gravity has on our body, then the semicircular canals, which respond to rotation or angular rotation. So in this video, we're going to focus on the semicircular canals. The next video will cover the saccule and the utricle. Let's go ahead and dive in. So the semicircular ducts that are in these canals here, they have hair cells, which respond to mechanical distortion by the fluid that's inside of them. So there are three semicircular canals in each inner ear. We have the superior, which I usually call the anterior canal, the posterior canal and the horizontal canal. So that superior or anterior canal responds to a nodding of the head, so moving forward and back. The posterior canal responds to tilting the head side to side, so bringing your ear towards your shoulder, then the horizontal canal responds to rotation. So when you swivel your head from side to side. So information about all three types of those movements, obviously I can move my head in any direction I want, and it'll stimulate more than one of these ducts. That's going to tell the brain where my head is in space and how it's moving, and the reason that's important is because then I can change the contraction of my postural muscles or I can move other parts of my body to make sure they don't fall over and I can see where I'm going, et cetera. All right, so how does this actually work? So when your head moves, the liquid inside these canals sloshes around. So if I turn my head, that's going to cause a sloshing around of this liquid inside these canals, and it's actually going to cause the receptors, the hair cells, which are there at that, the cupula, and then we have what are called stereocilia and one long kinocilium. They're going to bend, but in the opposite direction. So as I move, the liquid's going to slosh in the opposite direction, and it's going to cause them to be stimulated. But the information these hair cells are sending to the brain is what tells the brain about my head position, et cetera. That information is actually going to be sent through the vestibular ganglia to the vestibular branch of the vestibulococular nerve, which is cranial nerve 8, and then it's going to synapse with vestibular nuclei in the brain. So this is going to be how your brain receives information about rotation of the head in any possible direction. So how can we fool though? I'll give you a couple of examples. So if you spin around really fast and then stop, this liquid is still sloshing around, so your brain's going to think you're still moving for a while longer. This is why I would never get on a ride like this, but this is why you'd feel dizzy after a carnival ride, a amusement park ride, these types of things, or just spinning around in a chair, right? Just doing those types of things. I remember an incident I had with the teacup when I was a kid, so I don't do these spinning rides anymore. But that's why, the liquid is going to slosh around after your body's already stopped moving. Another example that students often bring up to me is when they get the spins, if they consume too much alcohol. So alcohol thins the blood and it actually changes the density of the fluids that reach the cupula compared to the blood. So this can actually distort these hair cells even when you're not moving. So you might be sitting or standing or lying perfectly still, but the brain is receiving information that you're moving, which is why it may feel like the room is spinning or the ground is moving underneath you. It's actually an issue of the fluid density, triggering these hair cells without movement. All right, so that's these semicircular canals and how they respond to rotational movements and help maintain equilibrium. I hope this helps. Have a wonderful day, be blessed.