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Hello. Hello. Hello. Can I uh can someone in the chat just confirm if you can hear us? Just type a yes or just a quick audio check? Ok. So got a couple of people joining. So I think, right? And if you can load up the powerpoint, then we'll get started. Yeah. Have you? Ok. All right. Let me see that. Yeah, I can see it. Ok, I think. Mm. So um but I think I'm very, I'm fairly confident that the audio is working. So. Ok. Hi everyone. So first of all, welcome to the uh audio auditory and vestibular lecture as part of our neurology lecture held by Ray Islam. He's a uh a fifth year student at Imperial and this is part of the Oh, ok. No, we've got confirmation. We have audio, we have visuals. So good start. So again, this is this is our lecture as part of the neurology series and glad to see that we've got some people in typing in the chat. So he'll be hosting this lecture. If at any point you have any questions don't hesitate to ask and type them into the chat. I'll try and flag them up if they don't get answered and we'll direct them to as well. And yeah, I hope everyone has a good time. Thank you very much. Ok, cool. Um, I'll make a start then. So just to go through, um, all destroy and vestibular is something that I think a lot of people find quite difficult. It is something, a lot of people I think are imperial at least don't really understand. Um, I know a bunch of people who found it completely nonsensical and the lectures that we were given were awful. So I there's a lot of people who just don't understand any of it and I think people can get quite lost in the weeds when it comes to it as with a lot of neuro. So this is gonna be a bit different than normal lectures in that. I'm going to start with the very basics with the like little foundations. I'm gonna explain it like it's five like your five and then we'll add some detail on afterwards and hopefully that should make it easier to understand what's going on. Um So we'll keep it simple and then we'll move on to detail. So all the vestibular systems both mainly within your ear, your ear sits within your temporal bone. The very basics of it are there are, there are three segments to your ear, there's your external ear, your middle ear and your inner ear. And the only really important part you need to understand is that your external ear and your middle ear are responsible for capturing noise and then amplifying it. And your inner ear is what actually hears your noise and helps maintain balance. As simple as that going, each by each external air is made up of something called your pinna or your auricle, which is what people typically think of it as the air moves quite easily is quite round. And the idea is that it should capture vibrations, which is what sound is. It's just vibrations of air captures vibrations, moves them into the opening inside your eardrums, which we call the external acoustic meatus or your auditory canal. Once all that audio is trapped, those vibrations are trapped, they kind of bang back and forth inside your auditory canal up until they hit something called a tympanic membrane, which is just a little flat sheet of membrane, basically connective tissue. And that again, um almost like a drum hits back and forth and back and forth and back and forth. The lymphatic membrane which has now captured that sounds as vibrations is connected to three bones inside your middle ear, the malleus, the inches incus and asap typical trivia question is that those are the three smallest bones in your body and they're essentially a bit like a um connected mechanism. Tympanic membrane hits the malleus, which is connected to the incus, which is connected to the stapes, one hits the other. So every time your tympanic membrane is vibrating back and forth cos you've heard something, it will hit the malleus. So the incus hit the stapes and that helps amplify sound. Um almost as if you're hitting a drum, the small force of your hand hitting that drum results in a really big sound because of all the ads like that. Right? That's essentially the only purpose of that. And so all I need you to remember is that the tympanic cavity, which is your middle ear, the only purpose of that is to amplify sound waves. That's it. Once we get to the inner, you've got two structures. One is called the vestibular apparatus, which is I'm gonna start drawing now, vestibular apparatus, which is this thing that's for balance and equilibrium, that's your vestibular system. So we're gonna put that second, your cochlea, which is this, there's a little shell like a snail conch that's responsible for hearing sound. So going again, back and forth sound hits your outer air, bangs back and forth inside your ear canal, hits your tympanic membrane, which then hits your middle ear bones, those amplifiers that sounds and then it hits your inner ear, your inner ear is what actually hears sound. And you've also got a little bit of a system that helps with balance in terms of that little conch shell, that little snail shell. I'll go into the actual detail of this later. I wouldn't really worry about these layers for now, we'll cover the detail properly. All you need to understand is that you've got these kind of loops that go throughout the conch shell and inwards. And each one of these loops is where you hear sound. This little part here, which is the scalar media that circle right there. That's where you've got cells that can actually hear sounds inside of. Those are these hair cells right there. Those has cells feel vibrations through this, which is just fluid. And every time that your fluid moves cos it vibrates those hassles pick it up and that gets converted into electrical activity which goes to your brain. So going back again to the very start sound goes into your outer ear, goes into your middle ear gets amplified, goes into your inner ear, which is this conch shell type thing goes into this fluid substance vibrates that fluid substance bangs against some cells, which are these hair cells right here. And every time your ear vibrates on the inside, those hair cells brush up against it and that gets converted into electrical energy, which your brain perceives as sound. If you've got really loud sounds, those hi hair cells will vibrate more, will get hit harder. You'll get more electrical activity and you perceive that as a larger sound. If it is small sound and you only hear it a little bit, those hair cells will only brush up a little bit. And so you'll perceive it as small sound cos the electrical activity will be smaller. We'll go into stuff like organ organ of corti and basil membrane in a little bit in terms of your vestibular apparatus. The only thing you really need to understand is that you've got three semicircular canals and those are responsible for angular rotational balance. So every time you turn your head left or right or forward or backward, the semicircular canals are what are responsible for understanding that things are moving. You've got all of this loop which is full of fluid similar to this shell. And then at the base of each one of these canals, you've got this thing called an ampulla right in the middle. This pink thing here is called a Crista, which is more hair, so more hair cells. So the difference is, whereas with, with hearing those hair cells would brush up and vibrate and that's how you'd tell that you were hearing something right here in the semicircular canals. The movement of fluid right next to the hair cells is what tells balance. So if you move your hair or your head to the left, like rotate it down to the left fluid moves around these canals. And the movement of that fluid is understood by those hair cells to show you that something's moving, you've got semicircle canals on the left ear and some on the right ear. And so any movement that moves stuff away in the left ear will move stuff towards it in the right ear, your brain will take both of those inputs and use that will do some electrical map inside your head and essentially movement of fluid because you've moved balance is what tells you your, your balance or your equilibrium, et cetera, et cetera. The other two stuff you need to know about the the apparatus are these two things called a uric and saccule. Your semicircular canals are responsible for rotation, angular rotation, that kind of thing, right? Your uric and circular responsible for longitudinal motion. So, whereas your semicircular canals can tell if your head is moving from one side to the other, your uric and circular can tell if you're stationary, but you're moving from one location to another location exactly how fast you're moving and what direction you're moving, et cetera. We'll go over exactly how a little bit. But all you need to know for the very foundations is that your uteral and saccule can tell you're moving in a single direction. OK. That is the very foundation, very basics, air captures noise, middle ear, inner ear, then it picks it up as electroactivity. Your vestibular apparatus is sort of a bunch of fluids that move around. And depending on how it moves around, you can tell whether you're moving from side to side or from one direction to another. Does anyone have any questions about that? And does any of that not make sense before we start adding some detail into exactly how all of that happens biomechanically, I'll give it like 30 seconds for anyone to type anything on the chart. Assuming all of that makes sense, then you should have the broader understanding of technically what's going on and then we can start adding some proper detail into what's really happening. Fine. I'm gonna take the silence as a yes, things are OK. So we'll start with hearing and then we'll do the, the next um So hearing that snail shell that I mentioned from earlier, which goes round and round and round and round and round. If we were to try and lengthen it into a single strip, it would look like this. And the essential aspect of this is that your stapes, which like I said was that bone from the middle ear is connected to this thing called the oval window. It's not actually a window and that nothing enters or leaves it. But um it is where the stapes connects to your contra. So um this over window, I wanna say is a bit like a bubble, your round window, which is this. So over window is this round window. Is this both are a bit like a bubble. Um Here's the best way I can explain it every time that a vibration, which is what sound is, every time a vibration hits your stapes, it will smash up against the over window which will push fluid throughout all of this, which is essentially just this. So you've got this kind of fluid filled capsule on the outside, which is full of something called Perilymph. It's basically just water is the only important thing. And every time that your stapes hits the over window, it pushes fluid forward basically to try and use it as a proxy for vibration. So every time you're outer ear catches vibration moves into your middle ear which moves into your inner ear, which moves into this. And every time you hear a sound wave, it gets transmitted as like a physical movement of fluid. The reason why you have this round window at the bottom is because water generally has a lot of hydrostatic pressure. You can't really compress water. And so the only way that you can allow water to move back and forward is if you have a bit of a give at the end, so this round window here just moves back and forth as and when water is moving back and forth, um it is a USB stick. But if you imagine this as your sound sound goes up and down and up and down. And depending on how much it vibrates or how much force it vibrates with your ear is telling that there's sound happening, right? If there is no gift, this can't move, cos water cannot be pushed. So the only purpose of the over window is to give it some gift. So you can move up and down. Simple as so your over window and your round window are just moving back and forth again and again and again, the only purpose of this scale of a stabili and skeleton pani is that your water is moving back and forth. And every time it moves back and forth, it brushes up against this thing here, which is the scale of mei in terms of a 3d model of how that looks stretched out. It's basically like this. So every time over the window is here, I'll type that out. Other window is here. Every time anything hits the other window, it vibrates all of the Perilymph, which is just external fluid etymologically. And that goes all the way here and then wraps around to go through the Scala Tympani. So you've got your scale of vestibular up here. Scalar Tympani at the bottom and it just goes round and round and round in the middle here. You've got your scale of media media just means middle scale just means like long essentially is all I want you to understand. There's this diagram on the left hand side that I've seen used a lot. I think it's quite confusing. So this diagram on the right hand side is meant to be a little bit more simple. The only really important thing you need to understand here is that you've got in terms of scale and media, we're talking about that a anatomy. Now you've got your fluid that goes through the scale of vestibular and that wraps around all the way down to the skeleton panny. So it's going back and forth and back and forth. By the time that fluid has reached the skeleton panny and the skeleton pani Perilymph is vibrating that fluid then vibrates against something we call the basilar membrane. The basilar membrane has a bunch of hair cells and those hair cells are responsible for picking up activity. So every time your fluid moves through the skeleton panny vibrates the basilar membrane membrane. And those hair cells, which are these little things here hits this very, very hard flat membrane called the tenor tectorial membrane. Every time, let's say there's a really loud vibration. So there's a been a very loud noise. Your skeleton panny will vibrate a lot and it will move upwards that will push the hair cells into the scr into the tentorial membrane and that activity will get recorded as electric activity. We'll explain exactly how that gets recorded in a little bit moving on. The other thing that's important you understand is that there are outer air cells and inner air cells and those are arranged tonotopically tonotopically. It always confuses me that way. The essential part you need to understand about that is that you've got this very thick area right here and this very thin area right here. So if you've got this kind of conch shell like that and we straighten it out so that it's lengthways, the end part here which is in the middle of your conch shell is this part here. So the end of your or the the very middle of your concha of that kind of shell structure, which flattened out is the very end of that shell structure is very thin and that very thin structure vibrates the most at low frequencies. So a very like um if you can hear this very like kind of low noises hums at the very middle right next to the staples near the oval window, it's thicker and that thickness predisposes to vibrations, a high frequency. So high pitch noises think of like birds chirping. So depending on the vibration of the noise, different parts of this membrane will vibrate your hair cells know whether it's high or low pitch depending on where those hair cells are. So if you hear a really loud noise, this part here will vibrate really, really heavily and your brain will be able to tell because it's those hair cells that it's a high pitched noise. If it's a low pitch noise, these cells will vibrate and your brain will be able to tell that it's a low frequency because it's those hair cells going very deeper into the anatomy. This is what it looks like on a on a cellular level. You've got one inner air cell here and one outer cell here. And the important thing you need to understand is so, first of all, this is the organ of corti that we described earlier is these hair cells and the basilar membrane, that's the organ of corti. There are three outer ear cells and one inner ear cell, you are in a ASL which is this picks up information. So we call that afferents. So when you get a vibration, this inner air cell goes into what we call the cochlear nerve, which is this right here, cochlea otherwise known as cranial nerve eight. And that picks up information. These out of three A cells do pick up information but they don't actually hear for you. What they do instead is they pick up whether vibrations are really strong or whether they're really weak. Imagine that you've got a really, really strong vibration. Imagine you had gunfire, the amount of vibrations that is gonna cause you is gonna be picked up as a, as a huge amount of sound and that amount of sound is gonna just destroy the amount of electrical activity inside your brain. It's gonna sound really loud, it's gonna cause you pain. It's a lot. So what these three outer ear cells do is if they pick up that there's a lot of noise, they are linked to your tectorial membrane, which is this thing, this kind of flat sheet, I'm gonna change color cos this is getting confusing. Now this oh hold on this flat sheet. Here is your tectorial membrane every time your hair cells and your hair is right here, bumping into the tectorial membrane, it causes vibrations which enables you to hear if the noises are really loud. Those efferent air cells hear, these ones will stimulate the tutorial membrane to relax a little bit, which means the brushing up of the that hair against that membrane is gonna be a bit weaker, which basically means that you stop yourself from hearing noise, that's too loud, that's not a media because you hear it at the same time as this. So you get this kind of effect where you hear a really loud noise and everything kind of goes quiet for a little bit. And that's cos these efferent fibers are trying to counteract that really loud noise and protect yourself by weakening your tectorial membrane. So you can't vibrate as much in terms of specifically how that happens. The important thing you need to know is just that your stereo, which is that, which is those hairs on the top of your, of your hair cells. Every time they brush up against your pictorial membrane, they depolarize. And when they depolarize potassium gets opened, that potassium opens a um neuro occurrent which then transmits into your cochlea nerve, which then hits your vestibular cochlea nerve, which goes to your brain, your endolymph, which is what your scaler media. So this thing here, scale of media, your scale of media is full of potassium. And so that potassium will move from the endolymph, which is that fluid filling, the scale of media into your hair cells that will end up activating your cole of. Does that make sense? Again, I'm gonna take radio science as sure and assume things are making sense to someone. So again, bringing you back to a very, very broad level sound goes into your outer ear gets trapped by, it, goes into your ear canal, hits your tympanic membrane. Your tympanic membrane is attached to your incus malleus and stapes that amplifies sound. Your stapes is attached to your over window, which then pushes water or perilymph inside your scale of vestibuli all the way around into your skeleton. Panny goes back and forth and back and forth at the bottom, which is right here. It vibrates against your basilar membrane, which is right here. That vibration pushes your hair cells into your tectorial membrane. And every time your hair cells brush, they depolarize or they, yeah, they depolarize a bunch of potassium moves in which is what caused the depo, which is what causes the depolarization, which then causes electroactivity to be sent to your cochlea of. And that's how you hear. And depending on how much it vibrates. More potassium vibrates in or moves in. There's higher depolarization, more activity is transmitted via the cochlea nerve. And so you hear louder sounds depending on whether the sounds are higher frequency or lower frequency, they'll be heard at different parts of that basilar membrane by different hair cells. Your brain knows which hair cells are responsible for which sounds and that's how you hear high frequency and no frequency. Ok. Once you've had all of that, I'm just gonna check. No. Yeah. Once you've had all of that, that will then go by a bunch of neural pathways throughout your brain, there are a lot of different systems that use a or auditory information to match things. You don't need to learn all of them. I've kind of muted this because it's not really important. It's just helpful I think to understand, but you don't need to memorize it. Um Your auditor information goes to your cochlear nucleus, which is this, that can tell whether things are radical. So if you hear noise above you or hear noise below you, your cochlear nucleus is what will identify that information and that's in the brainstem and then both your left and right cochlear nerve information will hit your superior olive and then your medial superior olive and then your last superior olive and then your inferior colliculus, et cetera, et cetera, et cetera. You, you don't need to know all the pathways. Um You can't tell whether something is left or right without hearing it from both ears, which is why you need to have both pathways before you hit the superior olive. The suffice to say all that information goes into your cerebral cortex, which is then processed in your primary auditory cortex and your secondary auditory cortex. And those are in the temporal lobes, keeping in mind your areas in your temporal bone. So it's very, it's very close to each other. So your cochlear nerve goes from your temporal bone down to your brainstem and then back up into your auditory cortex. Ok. So now that we understand how all that works, there are a few ways that things can go wrong. We tend to classify them into conductive deafness or sensor sensor, sensory neural deafness. I hate that word to you. Conductive deafness is where your out of air or your middle ear are blocked and your sensory neural deafness is where your inner air is blocked. Keeping in mind, your outer air and middle ear is just responsible for hi for capturing an amplifying sound. Your inner ear is what actually hears it. So if you've got some kind of blockage or some kind of issue with your outer ear or inner ear, you've got conductive deafness. So you've got some kind of issue with your nerves or your inner ear, which is what actually hears for you. You get sensorineural deafness. There are a bunch of different things that can cause either with conductive deafness. If you've got some kind of obstruction that could be wax or it could be bone growth that blocks air essentially moving through your external canal. You can have a perforated tympanic membrane, which is where that membrane is, is like it's essentially shattered a little bit is torn because of that. It can't vibrate properly, which means your in your middle ear can't capture noise from your tympanic membrane. So you don't hear it properly. Baral trauma, which is excess pressure, which can push your tympanic membrane to the extent that it gets torn essentially since or neural deafness is where you've got a, a nervous issue or you've got an inner issue or a few of those a little bit. Each after I've explained the next few slides, loud noise exposure can reach a point where it's vibrated your inner ear so much that things are a bit out of whack. And so your hair cells are kind of so depolarized that they can't repolarise for a little while. Many years, diseases, excess cochlear fluids. I'm gonna talk about that a little bit in a bit. Um Antibiotic toxicity can just cause damage essentially to inner ear structures. That's all you need to know an aging or presented by a qis is where you lose hair cells. So as you naturally, as you naturally age your hair cells kind of die off a little bit. The first hair cells to die are the ones next to the over window cos they face the highest vibration and so those will be the highest pitch ones, which is why when you age, you lose your highest pitch sounds first. Um It is why the hearing test for age, for the hearing test for hearing loss goes by frequency and you can tell what age you're at, depending on whether you can hear high frequencies, young people can hear really high frequencies like 20,000 kills. Whereas elderly people can, can barely hear that if at all clinically, the way that you tell between the two are Weber and Rin tests. Weber's test is a bone conduction test. So you take a tuning fork, slam it against the table and you put it on the front of your, of your head right here, right above your nose bridge. Technically, your inner ear can hear bone conduction cos it's in the temporal bone. Whereas your middle ear and external ear can hear things depending on whether they're going through air. If you've got normal ears, you can hear both things completely fine. If you've got conductive issues, which is where you've got blockages of the external and middle ear, you'll hear more on your body because you can properly hear through bone conduction and you can't hear background noise like nothing, nothing in like just the sound of of white noise outside people talking, it doesn't go through, through air cos you've got a blockage, but you can hear that bone conduction. And so out of nowhere, this conduction or this sound that you feel vibrating through your, through your bone, through your nose, feels louder on the air. That's got a conductive issue, sensorineurally. If there's a sensory issue, your good at it will be a lot better. Cos you can hear things in the first place any transmission of sounds is reduced with a sentin neural issue. And so your good air is louder. Keeping in mind that the louder ear could be a good or a bad ear, depending on if it's conducted or antineural, you then do something called a ring test, which is where you take it to your fork. This time you hit the bone, which is the master process behind your ear. Once they can't hear that sound anymore, you pull it out. And if they can still hear it with that out of air or by air conduction, that means that they've not got a conductive issue. A normal person should be able to hear things better by a air rather than bone because the entire purpose of your middle ear is to amplify that sound. Um whereas bone conduction goes straight to your inner ear if they can hear bone conduction, but then you take it off and they can't hear anything auditorially that implies bone conduction is better than air conduction, which would then apply that. There's probably some concern neural issue. Small table there you learn over clinical practice in terms of getting used to seeing this and how it functions properly. But assuming someone has a conductive issue because they've got a blockage, they'll, they'll hear things better by b better by bone conduction. Inter they still hear things better by air because they, there's no, there's no amplification issue. It's just that everything is quieter. So when you do a ring test, it's louder in your normal ear rather than your left ear. Um But yeah, OK. Does all of that make sense to people again? I'm gonna take radio silence as an assumption that things are making sense to some extent quickly before I move on some examples of, of what would go on. Let's say someone has ear wax and he did a weber and a ring test in a Weber test. They would hear it louder. Let's say they've got wax in their right ear. They would hear it louder in their right ear on the Weber test because bone conduction is greater. They can't hear it through air when you do a rin test again, bone conduction is greater than that. So you press this tuning fork onto the mastoid process behind their ear. They hear it when it dies out and they can't hear it anymore. You put it in front of their ear and they suddenly can't hear it at, at all in the first place. They can't hear anything through their ear because they've got a conductive issue. They've got something blocking. If someone had, let's say a tumor, a tumor of their cochlear nerve, that meant everything was quieter. You would do a bone test, which is the R which is the rubber test. Sorry, you do a rubber test and things are quieter. The bone conduction feels quieter on the ear that has the tumor because everything is reduced, you then do the ring test and they can hear noise after you've pulled it from their bone to, to air cos there's no conductive issue. They can still hear noise through the air. It's just that the noises are really quiet because there's a sensor, sensory neural issue and transmission of the electrical activity from inside your cochlea is weaker. Ok. Um Vestibular system then in terms of how that works. So, like I said, there's this apparatus here, which is your cochlear apparatus that's for hearing. And then you've got your vestibular apparatus here, which is made up of your semicircular canals, which are responsible for angular rotational movements. So you can tell whether you're moving back and forth and left and right. And then you've got your utricle and your saccular, which are here or these little things here. And there is responsible for telling if you're moving from one direction to another. The better way I can describe it is angular movement again, left and right back and forward and longitudinal movement. So you're not really changing your position, you're moving from one location to another back and forth, from like left to right. Your head is in the same position, you're moving from one position, one location to another. The idea is your canals are essentially your gyroscopes to your rotation, your otolith organs which are your uric and your saccule. So these little sacs here are your accelerometers. They tell you how fast you're going and in what, what direction the idea is knowing all that information helps you maintain your posture, helps you maintain your gaze, um helps you maintain balance canals. First, anatomically, these are, are at 90 degree angles from each other. If you've ever played Minecraft, they're a bit like your xy and Z angles in terms of when you press F three or it does make sense to people, but they're in exactly this orientation. If you think of a cube like this, you've got your upward angle, your right and left angle and then you kind of transverse oblique angle. Each one of these. If this is one, if this is two and this is three, this is one, this is two, this is three. This one down here is measuring horizontal. This is measuring back and forth. This is measuring from diagonal to diagonal. Each one of these canals is specialized for tracking one kind of plane of movement. If you've done anatomy a lot, think of it as sagittal transverse and then oblique again, I suppose um internally, the way that you actually pick stuff up is like I said earlier, you've got these rings, those are full of fluid at the base of each one of these rings is an um at the center of that ampulla is a cupula, your cupula is full of hair cells. The Crestor is what we call the tip of those hair cells. Those hair cells every time you move from one position to another, your fluid moves because of gravity, as fluid brushes past those hair cells similar to in your cochlea when they got brushed up against your tectorial membrane. In here, they brush from side to side which depolarizes them, which sends potassium in which triggers electroactivity, which goes into your vestibular nerve into your sib cochlear nerve that your brain sees as activity um similar to your scale and media full of endolymph. These are also full of endolymph. And so the only really important thing you need to understand is you move from one position to another. That position brushes past em endolymph, which is this fluid inside these canals, brushes into the ampullar past the cupula. Those hair cells get brushed by that fluid which gets seen as rotation by your brain. Your oates work a little bit differently, which is that again, similarly, they have hair cells, but the difference is they don't tend to have as much fluid. Instead they have calcium, they have calcium crystals inside the center, they're attached to hair cells. And so whenever you're moving from one direction to another, that fluid brushes past those has cells instead of them moving because of gravity, they move because of motion in your semicircular canals, you're moving from one direction to another, which causes that fluid to move towards gravity, which brushes up against hair cells, which gets seen as rotation in this gravity is not really important here. What's important is movement because of motion. So as you move quicker, the fluid moves past these hair cells quicker, which drags them depending on whether it moves towards the tallest cell or the or not, you get depolarisation or repolarisation or hyperpolarisation, which causes increased or decreased neuronal firing, which your brain sees as increased amounts of motion in a certain direction. If you're going, let's say from left to right or up and down hassles will be moved up or down to different extents. Let's say you're moving upwards, your fluid will move downwards because it gets dragged. The best way I can explain it is imagine that you get stopped in a car, you're driving in a car really, really fast and then you suddenly slam on the brakes when that happens, you kind of jump forward right? Despite the fact that the car has moved backwards and stopped it a little bit. The same thing happens with the fluid inside your ternate. And if you're moving upwards, your fluids drags downwards, your hair cells drag downwards and your brain interprets that movement as we've moved upwards. Essentially, the reason why you've got longer hair cells and shorter hair cells is just because the length of the hair cell lets us identify whether we're moving upwards or downwards. Otherwise you just know you're moving it fast but not in what direction. Um OK, this next slide is gonna be complex. I want you to understand that this is paled out because you don't need to understand the specifics. The best way I can explain it is that your vestibular system is really important for maintaining eye contact and keeping your eyes balanced. When I move my head left and right like this, I can keep looking at the screen in one direction. My my eye is still looking at the exact same thing despite the fact that my head is moving left and right and back and forth. And your vestibular ocular reflex is what enables that. This seems very, very complex. But the only really important thing you need to understand is that your vestibular nerve is causing constant excitatory activity to your lateral rectus muscles. Your your lateral rectus muscles pulls your eye towards a direction. So your middle rectus pulls it towards the middle of your head. Your lateral rectus pulls it towards the outside of your head. If I move my head to the right, I get ex ex Tory activity that essentially activates the lateral rectus muscle that pulls my eye to the left to keep my eye in the exact same direction or put, looking at the exact same thing, this looks like a lot. But bringing it down. If I'm moving my head to the right, let's say, in a clockwise direction like this, your brain sends Exor activity to the correct rectus muscles inside your brain so that they move in a counterclockwise direction it is, it is basic as that your head moves one way your eyes go the other. So you're looking at the same thing despite your head moving to the right and your eyes moving to the left. This is the very, very specific breakdown of the exact nerve by nerve, by nerve action of how that happens. But you don't need to memorize that. You need to understand that the way that um your ocular reflex functions is that your brain balances any vestibular movement, whether you move right or left with ocular movement. Inversely, I move my head right. My eyes move left. My eyes are looking at the same thing. I move my head left, my eyes move right. I'm looking at the same thing where this goes wrong. Clinically, you see something called nystagmus if this is your eye and you've got, oh, that was awful. If you've got rectus muscles pulling in either direction, any time I move left or right, my righteous muscles will balance my eye out. So it's moving. OK. So let's say CN eights and CN eights, which is your vestibular cochlea nerve, which is where your vestibular impulse comes from. If there is an issue, something's going very, very wrong. Let's say I've got an issue on my left ear. I've got a vestibular issue on my left ear. My left is vestibular apparatus is swelling with fluid, which is what many years disease is. And now suddenly the fluid is not moving. Everything feels really icky and haywire. If this is your left ear and this is your right ear, this is not broken. I can't tell what's going on on my left side because all that information is just screwed up. All the activity on this side is now gone. And so my eye starts moving in this direction because my CN eight is pushing it, it's pulling it in this direction. Your brain can tell that your eye is in a weird in a weird position, cos your eye is starting to move to the left and you can see that it's moving to the left and your visual system is able to tell this is not normal. And so your visual system will kind of take over and drag your eye back to the right really quickly. Nystagmus is just a repeated series of this exact same thing happening again and again and again, you've got a vestibular problem on this side. Your eye moves to the other side a little slowly, your visual system can tell something is going wrong. So it pulls it back to the right. If that happens again and again and again, you get this kind of back and forth flutter and that's what nystagmus is. So with a lot of vestibular issues with a lot of balance issues, I'm gonna go a few of the next in the next slide. If there is some kind of equilibrium problem, there's a balance problem. There's a nor if there's a um vertigo problem specifically, I'll talk about what that means in a second. The cardinal sign of that is dys stags because balance issues cause ocular problems clinically, what we end up seeing is via. And oops, we can define whether a vestibular problem is peripheral or central similar to in your hearing. Whether something is conductive, whether it's your ears fault or if it's sensorineural, if it's your, if it's a nervous problem, essentially, whether it's a conducting a nervous conduction issue, which is confusing cos conduction implies nervous, but that's not how it works. Vestibular problems can be broken down into whether they're peripheral. So whether it's your vestibular apparatus, um or your cranial nerve ache, technically, or if it's a central problem, central being brain stem cerebellum, anything implying your brain is what's messing up here going through each of these in time. Vertigo, I'm gonna change the color back again to red. Um Vertigo, which is this is just this feeling of poor movement of it's almost like dizziness. When you're asking any patient about their symptoms, you have to be very careful about discerning between lightheadedness, dizziness and vertigo. Clinically, they're quite different things. Lightheadedness is just a sudden feeling of wooziness. Um That could predispose to anything like orthostatic hypertension or sudden drop in BP. It's not the same as vertigo. Dizziness can be described by patients as lightheaded, lightheadedness. It's not necessarily the same as vertigo, vertigo is an illusion of movement. It's where you, it's a sensory mismatch, essentially where you can see things, everything is stable visually. If you've got a vestibular problem, all the information you're getting from your ear is out of whack. You can't tell whether things are moving left and right. Your brain thinks your head is moving left and right, but your eyes can tell you're not moving left and right. Your brain doesn't really know what to do with that information. And so it manifests as vertigo, which is just this complete feeling of nausea and not really knowing what to do. Cos you're trying to correct for balance despite there not being any, like I said earlier, because of the VIP problem, you can get nystagmus, which is because your eyes are trying to correct for all the vestibular problems by balancing out if you've got a peripheral problem and that'll be in your inner ear, your labyrinth, which is the peripheral apparatus. Those semicyclic canals and OTs make up the labyrinth or the vestibular apparatus. Both are used interchangeably. You can get three specifically common issues. BPPV is the most famous one, benign paroxysmal positional vertigo. So that's where you get this kind of temporary sudden onset nausea. And that's because of carbonate crystals in the canals. Like I mentioned earlier, your came back, your oates, which are your uric and your saccule have these kind of crystals in the middle. Those are calcium crystals, sometimes those can leak out. And if they leak into your lateral canals, your semicircular canals out of nowhere, you've now got these crystals just screwing everything up. They interfere with fluid flow, they drag on your hair cells and you get this kind of nonsensical information that things are going very, very wrong. If you move in a certain direction, you can move those crystals next to the hair cells, which is why in BPPV, when people move their head in a certain direction that moves those calcium carbonate crystals, um next to your hair cells, you suddenly get vertigo because all the information that your vestibular system is telling you is telling you that you're moving a lot in a certain direction or in a certain way when that's not what's happening, it's just that some calcium carbonate crystals have been caught on your hair cells, even though you're not actually moving. Labyrinthitis is just inflection of the labyrinth, which is the vestibular apparatus, which is your semicircle canals and your uric and s so often you can get something like a cold. And then a week after a cold, you can get a post viral inflammation of your vestibular nerve. It's the nerve specifically that's inflamed here. That information will essentially affects transmission of your vestibular information to your brain. And that's why you get this kind of weird vertigo, this weird dizziness kind of nausea. Many years, like I said earlier, an increase in fluid that increase in fluid kind of throws your system out of whack cos fluid's not moving in the way it's used to. Your brain is used to fluid in your semicircular canal is moving due to gravity and in your uteral and saccule your o it's moving due to motion. And if there's too much of it, it's moving at different speeds, it's moving at different capacities, it's moving in high, in higher amounts or quantities. Things are just off a little bit. So in patients with many ears, we do things like recommend less salt, restrict fluid, et cetera because that reduces the amount of fluid in your inner ear. So you've got a central issue. Things are a little bit different because it's not specifically your vestibular apparatus that's broken, it's your brainstem, um or your cerebellum or anything in your, in your brain that's tracking that information. Those are very, very bad because they're probably either a tumor or a stroke. There aren't many other causes that could affect your, your brain stem or your cerebellum. And so those are obviously a, a massive concern because stuff like BPPV and labyrinthitis can be induced by a certain position clinically. The way that we tell between the two is we do something called the dix Hallpike maneuver. You don't need to know this. But I think it's helpful to understand, to help, helpful for understanding when you move someone in a certain position in BPPV, there will be a slight delay in terms of what's going on because you need time for those crystals to move or you need time for that information to be transmitted into the vestibular nerve. And so you get vertigo when you move someone like that, but it takes a few seconds like 5 to 10 seconds. If there's a central issue, it's got nothing to do with your vestibular apparatus, your brain is just broken. There's some kind of uh tumor impacting on the on the specific gray and white matter that's transmitting that information. So you move someone's head and almost immediately there's a media vertigo and that's how, you know, you have a central issue. Last thing is oscillopsia is a loss of that vestibular reflex, which means that not only are you getting nystagmus, you're also not really able to move your eye properly. And so any time you move, your eye doesn't stabilize. So any time you move your head, your eye moves with it and everything feels very bouncy. Ok? Um We've got 10 minutes left. That is a summary of everything I wanna say. If anyone has any questions feel free to ask. Um But yeah, I also realized that my slides are quite text empty because I've been explaining everything quite ver verbally. So I've included some very, very high detailed notes that include a lot more beyond what you need to know, but are very comprehensive that if you guys get these slides or if anyone's watching the recording of this afterwards, um and that stuff should round it up for you. But yeah. Ok. Sorry. No, no worries. It's just about everything. I don't, everything I don't have. So please ask, ask, I have been keeping an eye on the chat. I think it's been a really good lecture and thank you very much for having us. Uh uh uh Thank for having uh giving us this lecture, Ryan. And I've also just made the feedback form go live. So if guys are able to, that would be great. If you guys did fill in the, in the feedback form, I'm just pushing it on the chart right now and it will also get shared to the attendees that were at this lecture. So, oh, we got a couple. So John Jessica's question, the slides will be uploaded as well. I'll w once the lecture is done, if you do fill in the feedback form as well, we'll be able to make sure that we share the slides with you. They'll be on the metal website as well. I'll, I we'll have to convert into a PDF and then we'll upload it into um uh just the lecture title itself, the Neo Aor Vestibular and Visual Systems. So just keep an eye out for that. It should be there in a couple in either tomorrow or day after or relatively soon, right? But again, thank you very much for doing this lecture ran and thank you very much for everyone attending as well. We're glad that we got good attendance and please do fill in that feedback form as well. It helps imagine for things like portfolios and just later down the line for applications. And again, if you're able to fill in that form, we're able to just give you the, just the learning materials that we've as well. So it's also good for your learning and hopefully we can see you guys in the upcoming sessions as well. I believe every Tuesday and Thursday we've got a preclinical session on neurology and we outline once that topic is done, we've got topics such as endocrinology coming up next. So we've got like a few minutes left. Um I've tried to go over everything and make it easy to understand if there's anything that didn't stick or if there's anything anyone would like me to quickly go over again, please just let me know I'd be happy to, if not, I hope you guys have a nice rest of your day and, and equally you welcome. Just don't tell me if you'd like. I think it was just really well explained. I don't uh I think, I think, I think to be fair, the content was really well delivered and that we had thank you explanations as well from start to finish. So I don't really, uh so I don't, I personally don't have any questions, but again, thank you very much. For giving this lecture. I'll listen. All right. I'm, I'm a special pop off then. That's all right. That's all. Yeah, I think it's as well. Cool, cool slides. Ok. I, yeah, no worries. Just send it to me by email or whatsapp and then I'll be able to send it to. Yeah. All right. Have a nice rest of your day, ma'am.