 Hey everybody, Dr. O here. We're going to finish our discussion on equilibrium by talking about the saccule and the utricle, which make up the vestibule. So we've already covered the semicircular canals in the previous video. So the saccule and the utricle, they both respond to linear acceleration. The key difference is the utricle is more sensitive to horizontal acceleration, whereas the saccule is more sensitive to vertical acceleration up and down. All right. So the saccule and the utricle, we do have these hair cells and you'll see the hair cells resting on top of them is something called otoliths, these little stones that are made of packed minerals called Staticonia and that makes them very top heavy. So when there's movement in the head, it causes the otoliths to move and that's going to trigger these hair receptors. So relatively straightforward. All right. So the actual movement or how the brain understands what's going on here. So the macula is looking for these different types of linear acceleration. So like when gravity acts on the head as it tilts or if the head starts to move in a straight line, these would be examples of things that are going to stimulate these hair cells. So when there is these types of movement, the otoliths are going to move because of the force of gravity and then that's going to trigger the hair cells. And those hair cells are going to send information to the vestibular ganglia. They're going to send information up the vestibular branch of the vestibulo cochlear nerve, cranial nerve 8, and then it's going to synapse with the vestibular nuclei. So relatively straightforward. So when your head moves, if there's any impact of gravity on your head or linear acceleration, it's going to move these otoliths, which is going to trigger these hair cells, hair receptors. All right. Let's talk about kind of why we need it and what happens when it doesn't work. So here's an example of what's called the vestibulo ocular reflex. This is information from the vestibular and the semicircular canals helps control eye movement. So it's a neat example of how these systems work together. So the eye movement is controlled by the ocular motor nerve, the trochlear nerve, and the abducens, cranial nerves 3, 4, and 6. So if you're moving while you're looking at something, your eyes are going to move in the opposite direction to make sure you can still see it. So this is one example of how the information from the vestibule and your eyes are working together so you can maintain a constant vision on something while you're moving. Pretty cool. Now let's talk about what happens when it doesn't work. So a real common example of that, excuse me, is something called BPPV, or benign proxysmal positional vertigo. I had many patients that had this type of vertigo when I was still in practice. So these otoliths can actually detach from where they're sitting on top of these hair cells, and they can land anywhere, but they can actually land inside one of the semicircular canals, especially when you're lying down. So if this happens, it's going to cause the semicircular canals to send the wrong signals to the brain. So it's going to confuse the brain and can lead to spinning and dizziness, these kinds of things. I'm going to show you an image. If you've never had vertigo, here's how I imagine it. I'm going to get off of that image so you don't get sick, but I've had patients that say that's what the world looks like when they're having these attacks of benign proxysmal positional vertigo. Now, thankfully, there's a treatment here. It's actual manual therapy or a movement-based technique called the cannolith repositioning technique. I'm not going to show it to you here. This is not medical advice, but if you have these types of conditions or know when it does, there is hope, thankfully, with the cannolith repositioning technique. I've done it. I've had people that laid down having vertigo and got up, and they didn't have it. It's pretty cool. So this is an example of when it doesn't work, though. All right. So that's the sacculomutricle, which make up that vestibule, which responsible for sending information to the brain about gravity and linear acceleration. I hope this helps. Have a wonderful day. Be blessed.