 When you think about your ear, you definitely think about, oh, hearing. Okay, we're done. See you later. Just kidding. There's definitely more to the ear than just hearing. The ear is involved in receiving perceptions of sound, but it's also involved in receiving perceptions of balance or position in space. And so let's look at the anatomy of the ear so that we can identify how exactly it works. First of all, your ear has three parts. Outer, that's what you can see. Middle, that's filled with air. And inner, that's filled with fluid. Let's make a note of that because that'll help us understand how it functions. Middle ear is filled with air. Really? There we go. And the outer ear is filled with air unless you jump in the water, in which case then it might get filled with water. This big leaf-like thing is called the pinna. Here's your ear canal. What is our technical term for that? The external auditory meatus, the external auditory meatus, the eem. The external auditory meatus travels all the way to what is this structure right here? That's your tympanic membrane. That's your eardrum. Eardrum is not good enough. Tympanic membrane. Your tympanic membrane separates the outer ear from the middle ear. Your tympanic membrane vibrates when sound waves hit it. Now, tongue was set up to receive chemical stimuli. Nose set up to receive chemical stimuli. Ear set up to receive mechanical stimuli. Sound waves. Sound waves, we're going to make them pink for fun because we have sound waves for fun, man. And they come in and they literally apply a force to your tympanic membrane. Your sound waves, most of the time, you can't actually feel sound waves. You can feel the air. But feel the mechanical vibrations that are making your sound when you talk. You can totally feel the vibrations here. And those vibrations come out. And the only reason why you hear anything is because my sound waves are going in and wiggling your tympanic membrane. Wow, that's really, like, intimate. A little disturbing, but we'll just stop right there. Your tympanic membrane starts wiggling. It's going to literally transfer the mechanical waves from the sound that's coming out into the middle ear. Now, if the waves just stopped, if we had just air between the tympanic membrane and our ultimate sensory structures, which are in the inner ear, then game over, you're not going to hear anything. Remove the structures in the middle ear, done. We got nothing going on. If we wiggle the tympanic membrane and we throw a bone like the Malleus into the mix, once we wiggle the tympanic membrane, what's going to happen to the Malleus that's touching it? It's going to wiggle, too. And then if the Malleus is touching, oh, you know, the Incas, what's going to happen to the Incas when the Malleus starts wiggling? It's going to start wiggling, too. And if they both know the Incas and are now touching who? My friend, Stapies. What's Stapies going to do? We got the wiggles going on. Now, this is crazy. Are you ready for this? Soundwave comes in at a magnitude of one. The mechanical movement has like a, I don't know, just I'm making up, just think of it as a size one. A size one earthquake. It's just tiny. After it wiggles the Malleus, the Incas, and the Stapies, your inner ear bones, I mean your middle ear bones, the size of the wave is going to be amplified 22 times. What? Okay, so that's like me coming in and going knock, knock, knock, that's a one. And what you hear when I go knock, knock, knock, 22 times louder than that. True story. I mean, is that like, wow, what a great setup. That's perfect. So what? Well, Stapies, who's Stapies touching? You guys, very important. Look, I'll make it green so you can see it. Stapies has its hands on another membrane called the oval window. The oval window and the tympanic membrane are the two structures that separate or that create the boundary of the middle ear that is filled with air. If a window membrane can vibrate the bones, which then vibrate a membrane, what is going to happen inside these fluid filled structures? Dude, have you guys been to the Discovery Museum? That's like my kids, well, back in the day when I was staying home with them all day long, we'd ride the bus to the Discovery Museum and we played with the water thing down there. And they had this like water wave maker and, oh, hours my children could stay and make waves at the water wave maker. And you push the, I don't know, it would walk in through the water and it would make this great big wave. When I'm yelling at you like this, because it's so exciting, the oval window is going to vibrate. And what did I tell you was true about the inner ear? It's filled with fluid. It's like a wave maker. We just transferred the anatomy of your ear. Dude, this is so freaking cool. We just transferred this mechanical sound waves into water waves inside your inner ear structures, which include your cochlea. Okay, we can't have it be that color because you can't see it. Let's try black. What novel idea? Cochlea. The cochlea looks like a little snail. And these guys have fluid filled in them also. Here are the semi-circular canals. Here comes the wave, a wave maker, because I'm yelling at you and you hear me. So the waves come in depending on how far the waves go up the cochlea, that will determine the pitch of the sound that you hear. So as I'm talking to you in all these different pitches and you can hear like all these different accents and incitements and whatever is happening, it's happening because the waves are like rushing in at different distances into the cochlea. All right, it's a mechanical wave. Guess what? You've got cells lining the cochlea. And I'll draw you on. It looks a little something like a look of this. Does this look kind of familiar? They're called hair cells. Hair cell and the hair cells synapse. Send messages to who do you think? Sensory neurons. Okay. Hair cell has its little twangers in the fluid. So when I'm yelling at you and the fluid wave comes in and the hair cell appendages, twangers, move. If they move this way, then the hair cell says, dude, send that message to the brain and fires a message to the brain. When they move back, it says, oh, there's nothing going on. Everything's normal. Really? And that's true. And that's how you hear it happening right now. What about these semicircular canals? The cochlea is where sound happens. The semicircular canals are involved in three-dimensional perception of position. So if you are on your side, now this is also just shockingly cool. Also fluid filled. However, the sound waves don't travel in this structure. Instead, true story, dogs, there are rocks in this thing. What? There are. And you know what? Those semicircular canals are set up. No, I have no idea because I'm spatially challenged. But I can visualize two axes, like an x and a y. And then I know that somewhere there's a z and then there's another axis that makes it three-dimensional. And those semicircular canals are set up to perceive all orientations of space. So if I knock my head over this way, they're set up so that the rocks in the tubes, right, are going to fall because of gravity in a specific orientation in those three tubes because of how they're set up in three-dimensional space. You totally understood that, didn't you? Because I'm so skilled at explaining three-dimensional things. But here I am with my head on my side because all the rocks fell in my ear. And my semicircular canals are saying, really, why are you sitting there with your head on your side? I could probably fall asleep in this position because, well, you just will stay focused right now. The rocks just fell back. I totally have a perception of, oh, yeah, I moved. I'm standing back upright again. Oh, the rocks just fell. And they send the message for three-dimensional space. Now, they are fluid-filled. So if you get waves going through the fluid-filled semicircular canals, if you get it by spinning and then you stop, do the waves stop? No, which is why you feel like you're spinning still. When you are not spinning, you are not. Dude, the air is amazing. Now, we have some information coming in regarding balance, perception, three-dimensional, location, and space. We've got some information coming in regarding sound. Let's talk about how we're going to send that information to the brain and how we're actually going to process. Like, what's the pathway once we get into the brain? But first of all, pat your ears Dude, you guys are amazing.