Understanding Eye and Ear Anatomy

All right, so this is the second chapter of this last unit, and we're going to be looking at the senses. As I said, we'll be focusing just on the eye and ear within this chapter. So we won't be doing the entire chapter, but doing the eye and ear to correspond with what we're doing in the lab for the anatomy of the eye and ear. So the first thing we're going to do when we talk about senses is understand that there are special senses as well as general senses. Special senses, as you can see listed here, are olfaction, gestation, vision, equilibrium, and hearing. We are going to focus on vision, equilibrium, and hearing, as those organs on the ear are responsible for those sensations. And special senses are things that require a sensory organ that is at a higher level of complexity than just for the general senses. The general senses, right, things like pain, temperature, touch. pressure, vibration, etc. are just provided by just sort of nerve ending that can respond to those sensations and send them into the special senses like vision and hearing which are the things that we'll be focusing on are provided by a sensory receptor that is much more complex than just the general sensory system. So the eye and ear are great examples of CVs are much more complex and general nerve ending like in your hand for example so we're going to start with the eye and with the eye we're going to be looking first at the accessory structures then we'll look at the anatomy of the eye and then we'll look at how this thing actually so accessory structures of the eye things like eyelids and lacrimal gland tears these are basically designed to protection, lubrication, support to the eye. So the things we're going to talk about, for instance, angles of the eyelid, disassociated straw. Eyelids are first. These are just an extension of the skin. We also call these palpabri. As you know, obviously, eyelids blink. And blinking is really designed just to keep the surface of the eye lubricated, right? You don't want debris and dust and other types of things. Kind of like little windshield wipers. That's work. It keeps the eye lubricated and free of dust. And these two eyelids come together, as I said, at the medial and lateral campus. on them which are much hairs that are going to help protect and keep things so that's one structure of the eyelids another one is the lacrimal car uncle which is a mass soft tissue in the corner of the eye you also have the conjunctiva we have a palpabril conjunctiva which is part of the eyelid of course and ocular conjunctiva thin epithelium covering the inner surface of the eyelids. You've probably heard of conjunctivitis, otherwise known as pink eye. So lacrimal apparatus is another really important thing. The lacrimal apparatus collectively includes the lacrimal gland itself, which produces the tears, but also sort of pathway and ducts for eliminating, distributing and eliminating, removing the tears as well. So lacrimal gland is the actual tear gland. We know tears are a, you know, accretion that can help keep the eye clear. We also know the emotions of tears when they come out associated with that. But this is really what we're looking at really more is just the lacrimal gland itself producing the tears. And it actually has a lysosome, antibacterial enzymes, which can also provide a really nice function of keeping the eye clean and clear, but also protecting it with the tears. So the tears basically pass through this lacrimal apparatus, including the lac sac and the nasal lacrimal duct, which ultimately then reaches the inferior meat of the nose. As you can see, the gland, lacrimal ducts, goes to the corner where you have the inferior lacrimal caniculus, lac sac, and drains into what's called the venous image. You can also see some of them. the muscles associated with the eye, the adipose tissue associated with the eye. Let me do your actual eye dissection later on. So the eye itself is a hollow structure and consists of three layers. You have an outer fibrous layer, a middle vascular layer, and then finally the inner neural layer or neural tunic, as we call it. And so it's divided into two cavities. You have a much larger posterior cavity, which as we said is hollow. contains a vitreous humor, which is sort of like a gel-like substance to keep the shape of the eyeball. Then you have a smaller anterior cavity, which also has a fluid circulating through the pelvic eye. You can see the eyeball itself is completely hollow. You can see the three different layers, starting from the outermost, middle, and inner layer, the lens, cornea, and so we want to talk about all these different layers. So, fibrous layer consists of two parts, the sclera, which is where you see the light of the eye, and then that continues and turns into what's called the cornea. And the cornea is sort of the transparent, relatively thick covering over the eye, and this is what helps with refraction and how we're able to focus image. Part of that, the lens and the other part, part of it is the cornea that helps with proper laser. So here you can see the outer layer, the fibrous, you can see the sclera, and then as it turns into the cornea, the anterior, just in front of the anterior cavity. The lens, of course, and the posterior cavity. The vascular layer is next, and it has several components. The iris, the ciliary body, which is attached to the lens, and helps the choroid, which is the vascular component. Choroid oxygen and nutrients. innermost layer, which is the neural layer or the retina, both the neural and the pigmented portion. All those axons of the neural part then come out the back and enter as what's called the paratheopic nerve. So here you can see the pathway, the visual axis, traveling through the cornea on the surface and then through the lens and ultimately getting focused directly on the fovea, where we have the highest concentration of our clearest viewing photoreceptors. So that's the outer layer, the cornea and the sclera. The middle layer is the vascular layer, also known as the uvea, and it has several functions. Number one, it's going to provide a route for blood vessels and lymphatics that support the eye, so the retina is directly attached to this portion called the choroid. And it allows for nutrients and oxygen to be delivered to the eye. So that's really a very important part of what this vascular layer does. It also can regulate the amount of light entering the eye, as this part is also part of your iris, which is the colored part of your eye, but also creates the pupil, and it's made of smooth muscle that can constrict and dilate, and so therefore change the opening of the pupil and therefore regulate internet. This layer also secretes and reabsorbs the oculus huma, which is really important to keeping the pressure inside the eye at optimal levels, but also can control the shape of the lens. You have what's called the ciliary body, which, as we're going to see, is really important to focusing, and altering your focus, basically, if you're looking at something close or something further away. All right, so the vascular layer, again, consists, the first part is the iris. And the iris is made of smooth muscle, which we also refer to as papillary muscles. And these smooth muscles, again, they have, it gives you the color of your eye, but they actually can also contract, change the diameter of the pupil. So smaller diameter or larger, right? You've got pupils dilated maybe at one point in your life when you're getting vision tested or something like that. And you can see in this image, you have a pupillary dilator muscle, and you also have a pupillary constrictor. constrictor muscle. And the dilator muscle, right, extends radically away from the edge of the pupil and dilates. You have more light entering. And you can also have a constriction of smooth muscle, that pupil area constrictor muscle, and you can make that opening smaller. So what stimulates the activity of either constriction or dilation, constriction is stimulated by an increase in intensity of light, but also an increase in parasympathetic stimulation. So we have more light coming in, sort of a reflex response is to constrict that to regulate the amount of light coming in, but also So parasympathetic stimulation, right, rest and digest when you have the time, perhaps, when there's less light coming. On the other side of things, we have dilation. What stimulates dilation? Well, less light, right? So we have less light. I'm going to dilate more to get more light into the retina so I can see. But then also increased sympathetic stimulation also can cause, right, sympathetic stimulation is fight or flight. That's when you have the highest. Levels of activity as we talked about in the last chapter and so that's going to lead. So those are two extremes there with the pupil but that's regulated by this middle layer, this vascular layer. Part of that is also part of this vascular layers as I've said before is what's known as the ciliary body. Ciliary body The smooth muscle, essentially, is attached to the lens via what are called suspensory ligaments. And smooth muscle is kind of like a sphincter muscle, again, kind of like we just talked about with the pupil and the iris, is that the ciliary body can contract or relax, and depending on whether it's contracted or relaxed, it's going to change the tension on those suspensory ligaments that are attached to the lens, and thereby change the shape of the lens. So the lens actually changes shape. shape altering the refractive power and focusing power so we'll talk about the physiology of that process in greater detail coming up third really important part of this vascular layers let's know is the core and I mentioned this is the actual vascular layer that separates the fibrous layer from the retina and this is where we see oxygen nutrients the way this is essential we know that How detrimental it is when nervous tissue does not have oxygen or nutrients, even just for a very short period of time, you're going to see significant damage to the structure. So, a really important layer to deliver oxygen and nutrients. And so then the inner layer is the retina. The outer portion called the pigmented and the inner portion called the neural or retina, that's what we'll focus on. And then we have a nice opportunity when you do your dissection to see the retina on the inside of the eye when you slice it open. Pretty cool experience to see that. So this retinal part contains the visual receptors, and they're called photoreceptors. There are also other associated neurons that helps with the interpretation and conduction and modification of the images. And so the two primary photoreceptors that we're talking about are rods and cones. You've probably heard of these. Rods are highly sensitive to light, do not discriminate light colors. So that's what you use, like, for instance, Whereas cones are the ones that provide color vision, light. These cones are densely clustered in what's called the fovea, which is the center of the macula. That's where we want all of our images primarily focused. Cones, and that's going to give you the highest level. And so you can see your visual axis here goes directly back to the retina. focus in the fovea. Here's a nice image showing you the inner layer of the retina. See the rhizome region, but then you also have bipolar and ionic attached to that and then you can see the act together to send the impulse nerve to the brain. So as I said, all of these photoreceptors and other ganglionic nerve cells in the retina and other components, all their axons then exit out the back of the eye and the optic nerve. And where that originates exists because there are no photorecepts, only axons leading into the optic nerve. So as a result, you create this blind spot because light... striking this area because of notice because there are not any photoreceptors in location. So you can do sort of a test, a book that sort of shows how that works. But here is a really great image where you can see this pigmented portion and the neural part of the retina. And you need to exit the eye so we can get to the brain so you can process images. And so these travel out the back. This look. patient where all those axons are coming together and exiting the eye to go to the brain there are no photoreceptors there right you have photoreceptors over here you have photoreceptors over here but none right here right and so that's the we call the opt so that is what we see in terms of this process happening with sort of this blind spot because there's no photoreceptors at that location. All right, so, and here's a nice shot inside the eye of the macula and the blind spot at the optic disc. And then there's that test that I was telling you to try. You can try it in the textbook and you'll see one of those spots disappear and that'll demonstrate the presence of the blind spot. All right, so moving on to the chambers of the eye. The ciliary body and the lens basically divide the eye into a posterior cavity and a smaller anterior cavity. So if you look at this image you can see the posterior cavity is behind the lens and it's much larger. When you do your dissection, you'll do a cut sort of in that region, right, and you'll be basically dividing it to anterior cavity and posterior cavity. And in the anterior cavity you actually have two chambers, one in front of the iris and one behind the iris called the anterior-posterior chamber. But then of course you have the cornea on top of that. The posterior chamber, we call it the vitreous chamber, which has this gel-like substance that's humor. Here you can also take a moment to appreciate the ciliary body and the dispensary ligaments that attach to the lens. Like I said, we'll talk about that. So, aqueous humor, as we talked about, is also produced in this region. and it's the fluid that circulates within the eye and helps establish what we call intraocular pressure. It helps retain eye shape and give adequate pressure to the eye. In the posterior cavity, as I said, there's this vitreous body or gelatinous mass that you're giving your dissection. Hopefully, if the gel is still congealed, it will pop out, and you'll be able to see the gelatinous mass stabilize the eye shape, but also really helps support the retina. That retina needs to always be directly connected to the ciliary body on top of it, right? Or excuse me, the core on top of it. And so that gelatinous mass sort of presses and pushes up against the wall and keeps the retina directly attached to it. That's really important. A detached retina, which you may have heard of, is something that can obviously cause some... serious issues in terms of all right so the lens we saw the lens is attached to the ciliary body by the suspensory ligaments and as I said part of light passes through the cornea but also passes through the lens and so this lens needs to be clear okay and so the lens always needs to remain this In clear condition, it's filled with crystallins, which help provide this clarity and focusing power to the lens. And again, the primary function of the lens is to focus that image on the photoreceptors. And it actually has the ability to change shape. Transparency of the lens is essential. Any alteration of this, if you lose transparency at all, we call that a cataract. You've heard of cataract surgery these days, a laser to surgery really, for the most part, to remove. cloudy or just you know can't see as well through it no need all right so to understand focusing you'd understand the concept of light refraction light basically when it passes from one medium to medium with a different density if that image is going to bend it's going to refract think about putting like say a glass of water you can see the pencil in the glass of water cool right that's good The appearance of that pencil is going to be different, right, because you're looking at it through something of a different medium. And so that's sort of the concept you have with vision, right? It's bent when it passes from one medium to a medium of a different density. And as we know, light, to get to our retina, has to pass through the cornea as well as the lens. So those two things are what are providing the refraction so that it focuses directly on the retina. The array is not, the light is not. Directly, perfectly focused on the retina, then the image is going to be blurry, right? And you're going to use a third layer of the front. Cornea and the lens are not getting it done. That's why people look up. or contacts right to sort of provide that third level of refraction so the image is bent and hits the retina and direct okay so focusing is done at the lens right and as I said it's held in place by the sensory suspensory ligaments of the ciliary body okay the smooth muscle in the ciliary body act like a sphincter and so it can either contract or relax and if it contracts the ciliary body is moving closer to the lens closer to the lens, the ligaments will be a little more lax and therefore the lens is going to be rounder or more spherical. This rounder, more spherical shape increases the refractive power and allows you to focus things that are much closer, okay? When something is further away, the lens needs to flatten, decrease the refractive power so you can focus on something that's further out. So sensory ligament, excuse me, when the ciliary body relaxes, it pulls away from the lens, that's going to... tighten the ligaments a little bit, and then pull on the lens, and the lens will stretch out and there you have this focusing power based on what the ciliary body is doing. So here you can see the ciliary body, here's the lens, and you can see these suspensory ligaments that are attached. The ciliary body moves closer, which is going to relax the ligaments, or it's going to move away, which is going to cause more tension. When it moves away, it's going to flatten. When it moves closer, it's going to become more sparse. And that's what changes this, we call this accommodation of the lens, changes this ability to focus on whether we're looking at something closer in our field of view or something that's much further. And so here you can see with a regular lens, it allows you to look at close. The ciliary muscle contracts, it moves closer, and the lens becomes more spherical and focuses it rather than putting as much focus on the lens. further away, right? The ciliary muscle relaxes and pulls away from the lens, flattening it out, and then also focusing. So, clarity of vision, right? Being able to see something clear. As I said, if you cannot, if something's not focused directly on the retina, you're not going to see it very well, right? And so you've heard of like 20-20 vision, right? That's basically a comparison, right? It's someone who has Your vision compared with someone who has quote-unquote normal vision, right? And you can see, you know, details like oftentimes optometrists will use a board of letters and numbers. You guys have all seen that before, right? And at 20 feet, you can see what someone with normal vision can also see at 20 feet. So you guys are at the same distance, you know it's good, and we call that 20-20. Worse than if your vision is worse than someone with quote-unquote normal vision. Then it can be 20-30, 20-40, 20-50, etc. This means that what you need to see at 20 feet, someone with really normal vision can see much further, right? So that's what that means. And so part of the more common types of accommodation that occur, things like myopia, which is nearsightedness, right? This is being able to see things, obviously, pretty well. close range but things that are further out are going to be harder to see and a lot of it has to do just with the architecture of the eye inside the skull right if the eyeball is too deep or the resting curvature of the lens is too great it's not going to hit the retina perfectly right region at close range is typically normal because the lens can can accommodate for that but when you get further away the lens can't sort of make up the difference Third layer of refraction here, myopia is corrected with a divergent concave lens. It's going to adjust the focus. Hyperopia, which is farsightedness, another fairly common type of sort of issue with vision, right? Accommodation issue. The eyeball can be too shallow or the lens too flat. Again, you're going to sort of overshoot the retina, and it's not going to be focused directly. oftentimes older individuals become farsighted as their lens loses elasticity and so it's not able to really be focused properly. So again a converging lens here is going to help adjust that focus so it hits through. Probably heard of LASIK or PRK other types of keratectomy surgeries that basically try to repair this issue, right, to correct this instead of having to use glasses. It sort of replaces glasses. like in basic for instance they're actually reshaping the cornea right and trying to get it so that it has the right amount of refraction to get it focused directly on the retina so that's an option if you don't like wearing glasses and contacts and things like that you can have surgical care. So that's it for the eye what about the ear the ear is You know, pretty straightforward in terms of its structure. We have nice models in lab for the ear. You'll be able to see all these structures pretty simply. So we'll go over the structures real quick, talk about a few clinical applications, and then look at the physiology of the ear. So, the ear, the structure of the ear is in three components, external, middle, and inner ear. The external is what you see on the outside flap that sits on your ear. Also called the auricle or pinna, the direct sound waves funnels them into the middle ear. The middle ear is the airfield chamber that actually connects these sound waves and initiates the process of turning a mechanical or physical stimulus of sound waves into an electrical impulse. And then ultimately, the sensory organ for hearing an equilibrium is in the inner ear, and that's where the impulse will be created and sent on the vestibulocochlear nerve, cranial nerve number eight, which I know you guys are currently learning. So here you can see all those structures. You have the external ear with the auricle and the external acoustic meatus. You have the middle ear, which has the auditory ossicles and begins with the tympanic membrane. And then you have the inner ear, which again has the organ cochlea, which is responsible for hearing, but then it also has the vestibule and the semicircular canal. which are all right so the external ear also referred to as the auricle or pinup again basically is providing directional sensitivity sensitivity funneling sound waves deeper into our ear into the external acoustic natus also providing some protection to the opening of that pathway the external Acoustic natives ends of the tympanic membrane, which is otherwise known as your eardrum. And this tympanic membrane is really important. It's within a semi-transparent sheet. It basically responds to those initial sound waves that arrive in your ear and will then be conducted further deep. Also in the external ear, we have ceruminous glands. They secrete more of a waxing material. Obviously, you know, as ear wax, I'll call it cerumin. And that's really, you know, there's a purpose to it, right? Just keep foreign objects out of the tympanic membrane and slow, prevent or slow the growth of microorganisms or bacteria, things like that, trying to protect the ear, okay? So that's the external ear. The middle ear is also referred to as the tympanic cavity and basically includes what's called the malleus, incus, and stapes. It also has an auditory air tube, as I mentioned, which communicates with the nasopharynx. and also is a pressurized cavity. The tympanic, the three auditory ossicles, the malleus, incus, and stapes, are all attached to the tympanic membrane. And so when that tympanic membrane vibrates, these guys are attached to the tympanic membrane and create sort of a kinetic chain of movement. In other words, when the tympanic membrane vibrates, malleus will then vibrate, which will stimulate the incus, which will then stimulate the... the stapes and then that will create a pressure wave inside the organ, the sensory organ, which we'll talk about in a minute. So that's looking inside the ear. The vibration of the tympanic membrane, again, is really the first step in this process. It converts those sound waves into actual mechanical movement or distortion of those auditory obstacles. and then those auditory oscillators will conduct those vibrations. Now you've probably heard of pediatric ear tubes, right? Based on the architecture of the growing child, oftentimes kids, when they get cold, can get ear infections very easily because fluid can build up, and when you have fluid, it can put a lot of pressure on the tympanic membrane, and basically there's no place for the fluid to escape, and as a result, not only can it be painful, but bacteria can multiply and develop and treat. When you have an ear infection, well typically antibiotics, right? You get a bacterial infection, use an antibiotic to treat it. And that's fine if you get one or two or a couple in your life no big deal but if it's as often times the case with a lot of kids this happens over and over and over and over again every time they get an ear infection you don't want to keep treating the child with antibiotics right you want to hopefully come up with another method of treating that's another way of relieving these symptoms and so that's what pediatric ear tubes do right they basically create a conduit or a pathway for any fluid that might get trapped in that middle ear to escape And so I speak from personal experience. My kids have this done. Basically, the physician goes in and puts a small incision on the tympanic membrane, pops an actual little tube in there. It's like a little colored tube that's then going to allow fluid to escape, not allow pressure to build up, and not allow bacteria to form. And hopefully that can be used instead of having to treat the kid with antibiotics. That is a pediatric ear tube. So then on to the inner ear. The inner ear has this structure that has this bony labyrinth that surrounds and protects the membranous labyrinth on the inside. And inside that, you have a fluid called an endolymph. And basically, the stapes attaches at this structure at the oval window, and that puts a vibration and changes, distorts the fluid of the endolymph, and that's what's ultimately going to stimulate the nerve ending, which is going to send sound waves out. or excuse me, which is a depolarization of the nerve ending and send the impulse, turn it into an electrical impulse, right? That's the trick. That's what the ear has to do. That's physical stimulus, which is sound waves of pressure, and convert that into an electrical stimulus so that the brain. So anyway, so this thing is divided into three parts. You have what's called the vestibule, the semicircular canals, and the cochlea. And here you can see, here's the cochlea. That's the hearing part. Here's the vestibule, and here are the semicircular, okay? So they're all responsible for something a little bit different. If you take a cross-section through, you can see how this is organized. This is a cross-section through the semicircular canal, for instance, and you can see you have the bony labyrinth on the outside, and on the inside you have a membranous labyrinth. Inside those two spaces, you have a paralymp, which is beneath the bony labyrinth, and then you have an endolymph, which is deep inside the membranous. That endolymph is ultimately where we're going to see distortion that's going to stimulate the vestibule. It's responsible for sensations of gravity and linear acceleration. Semicircular canals are stimulated more by rotation of the head, but these two components are the ones that are responsible for equilibrium and balance. Cochlea is the part that's responsible for providing our sense of hearing. And so we'll look at that. Alright, so the oval window, you have these two structures of the round window and the oval window. The oval window is what's attached to the stapes, and the stapes is ultimately the last thing that distorts, which is going to establish a pressure wave inside this. So, hearing then is provided by this cochlea. The cochlea has nerve cells in them. Those that are responsible for that are what are called hair cells. Hair cells are in what's called the organ of Corti and has a bacillus membrane on top, a tectoral membrane on the bottom, and if the pressure wave passes through this endolymph, it's going to stimulate these hair cells, causing vibrations of the bacillus membrane, and that's going to stimulate these receptors. So here's a nice image of... For instance, a hair cell, right? You can see the stereocilia on top of those, the hair cell. So hearing basically works as these auditory ossicles vibrate and change. It's putting a pressure wave into the paralymp of the cochlea, right? And so frequency of sound is determined by which part of the cochlear duct is stimulated and intensity. determines how much of the hair cells are actually stimulated. So to understand how this process works, the actual physiology of hearing, we need to understand a little bit about the sound, right? And without getting into too much detail, sound consists of what are called waves of pressure. A pressure wave is essentially an area where you have air molecules together, and then right next to them you have it further apart. Very close bunch of air molecules together, another area closer to part. So those are wavelengths. It's a distance between each one of these waves. frequency is how often they pass over a fixed reference point in a given time. So these waves of pressure arrive and are produced when, you know, sound is produced, right? That's when sound is a physical process. So for instance, my speaking right now, my vocal cords are vibrating and producing those sound waves, or if you strum a stringed instrument, right? Think about strumming a guitar, you can see those strings vibrating and they're distorting and creating these pressure waves. that can arrive at our tympanic membrane ultimately in that wave of distortion. So sound is produced by energy as I just described. The vibration of vocal cords or a tuning fork or a stringed instrument, right, is producing these sounds. And the more flexible an object is, the easier it will respond to those pressures. So tympanic membrane has to be pretty flexible. It's like pretty thin types of strings. structure needs to be very sensitive to the sound pressure so I can stimulate. And so here shows sort of how that works, right? Like a tuning fork, you guys can place any one of those before you hit it and you can see it vibrating, but you can also, it's producing these air molecules, these sound waves, and these sound waves are then tunneled into the ear and ultimately arrive at the tympanic. Okay, and so this, these next six steps show that exact process. In the first step, those sound waves are produced. In any way, right, speaking, vibration of stringed instruments, other types of methods that produce these sound waves, right, they're ultimately going to arrive at the tympanic membrane. Once the tympanic membrane vibrates, that causes then displacement of the auditory ossicles. So tympanic membrane vibrates, the malleus then moves, that causes the incus to move, that causes the stapus to move. So that sort of is like a kinetic chain of motion. And the stapes, as we said, is attached at the oval window, and it creates movement of the stapes, establishes a pressure wave in the paralymp, which will ultimately lead down to distorting the bacillus membrane, which will ultimately cause vibration of the hair cell against the pectoral membrane, and that ultimately will lead to stimulation of the neuron ending, the cochlear branch of cranial nerve number eight, also known as the cranial nerve. Here you can see that in these images. So make sure you have a good understanding of those six steps and see how you're essentially the body or this organ, this cochlea, is converting pressure waves into actual intellectual. And to further understand that, there's this story I heard on NPR, and actually I studied this molecule a little bit in grad school. This is a... Triphae-1 protein is a molecule that actually opens when a certain sound wave sweeps over that channel. And so, again, it's a mechanically regulated channel. Remember we talked about channels that need to open to allow for depolarization to occur, to allow ions to rush into the cell? Okay, this one is going to open at a mechanical stimulus. And so that's what happens, right? Once that mechanical stimulus arrives, it opens these mechanically regulated channels, allowing the moves. Electrically charged ions pass in the flow into the hair cell and that ultimately converts it then into an electrical impulse that can be understood by them. Right? That's really the trick, right? Converting a mechanical stimulus into an electrical impulse. And this is where it happens. So if you click on the link, you'll probably have to pull up the actual slide itself and put it in PowerPoint in presentation mode. You should be able to click on that and go to the link. And it's just like, you know, a five-minute story. I think it will help pull together all of these things we're talking about. And so here are some images of a hair cell bundle. These hair cells are what you're able to detect but also amplify sound waves. And that trip A1 sits at the tips of those structures and allows for the impulse to be created as an electrical. So... Hearing range from softest to loudest, right, really is a huge increase. We never really used our full potential. Young children typically obviously have the greatest range, and as we get older, we really start to see diminished hearing capability. Basically, it's just a result of damage over time, right? We lose hair cells, right? Over decades and decades and decades of hearing all the time, we're going to lose some hair cells. And so... The tympanic membrane also can be less flexible, so it's not going to respond as easily to those sound waves. Articulations between the auditory ossicles will stiffen. You might see ossification at the round window, which is going to diminish how things can be transferred into the paralymp. So all these things can contribute to diminishing hearing as we accept the pretty typical symptom of aging. Alright, so that's it for the eye and the ear. Again, this will coordinate nicely with what we're doing in lab. Our last chapter for the semester will be the endocrine.

We are going to focus on vision, equilibrium, and hearing, as those organs on the ear are responsible for those sensations. And special senses are things that require a sensory organ that is at a higher level of complexity than just for the general senses. The general senses, right, things like pain, temperature, touch.

pressure, vibration, etc. are just provided by just sort of nerve ending that can respond to those sensations and send them into the special senses like vision and hearing which are the things that we'll be focusing on are provided by a sensory receptor that is much more complex than just the general sensory system. So the eye and ear are great examples of CVs are much more complex and general nerve ending like in your hand for example so we're going to start with the eye and with the eye we're going to be looking first at the accessory structures then we'll look at the anatomy of the eye and then we'll look at how this thing actually so accessory structures of the eye things like eyelids and lacrimal gland tears these are basically designed to protection, lubrication, support to the eye. So the things we're going to talk about, for instance, angles of the eyelid, disassociated straw.

Eyelids are first. These are just an extension of the skin. We also call these palpabri. As you know, obviously, eyelids blink.

And blinking is really designed just to keep the surface of the eye lubricated, right? You don't want debris and dust and other types of things. Kind of like little windshield wipers. That's work.

It keeps the eye lubricated and free of dust. And these two eyelids come together, as I said, at the medial and lateral campus. on them which are much hairs that are going to help protect and keep things so that's one structure of the eyelids another one is the lacrimal car uncle which is a mass soft tissue in the corner of the eye you also have the conjunctiva we have a palpabril conjunctiva which is part of the eyelid of course and ocular conjunctiva thin epithelium covering the inner surface of the eyelids. You've probably heard of conjunctivitis, otherwise known as pink eye.

So lacrimal apparatus is another really important thing. The lacrimal apparatus collectively includes the lacrimal gland itself, which produces the tears, but also sort of pathway and ducts for eliminating, distributing and eliminating, removing the tears as well. So lacrimal gland is the actual tear gland. We know tears are a, you know, accretion that can help keep the eye clear.

We also know the emotions of tears when they come out associated with that. But this is really what we're looking at really more is just the lacrimal gland itself producing the tears. And it actually has a lysosome, antibacterial enzymes, which can also provide a really nice function of keeping the eye clean and clear, but also protecting it with the tears.

So the tears basically pass through this lacrimal apparatus, including the lac sac and the nasal lacrimal duct, which ultimately then reaches the inferior meat of the nose. As you can see, the gland, lacrimal ducts, goes to the corner where you have the inferior lacrimal caniculus, lac sac, and drains into what's called the venous image. You can also see some of them.

the muscles associated with the eye, the adipose tissue associated with the eye. Let me do your actual eye dissection later on. So the eye itself is a hollow structure and consists of three layers. You have an outer fibrous layer, a middle vascular layer, and then finally the inner neural layer or neural tunic, as we call it.

And so it's divided into two cavities. You have a much larger posterior cavity, which as we said is hollow. contains a vitreous humor, which is sort of like a gel-like substance to keep the shape of the eyeball.

Then you have a smaller anterior cavity, which also has a fluid circulating through the pelvic eye. You can see the eyeball itself is completely hollow. You can see the three different layers, starting from the outermost, middle, and inner layer, the lens, cornea, and so we want to talk about all these different layers.

So, fibrous layer consists of two parts, the sclera, which is where you see the light of the eye, and then that continues and turns into what's called the cornea. And the cornea is sort of the transparent, relatively thick covering over the eye, and this is what helps with refraction and how we're able to focus image. Part of that, the lens and the other part, part of it is the cornea that helps with proper laser.

So here you can see the outer layer, the fibrous, you can see the sclera, and then as it turns into the cornea, the anterior, just in front of the anterior cavity. The lens, of course, and the posterior cavity. The vascular layer is next, and it has several components.

The iris, the ciliary body, which is attached to the lens, and helps the choroid, which is the vascular component. Choroid oxygen and nutrients. innermost layer, which is the neural layer or the retina, both the neural and the pigmented portion.

All those axons of the neural part then come out the back and enter as what's called the paratheopic nerve. So here you can see the pathway, the visual axis, traveling through the cornea on the surface and then through the lens and ultimately getting focused directly on the fovea, where we have the highest concentration of our clearest viewing photoreceptors. So that's the outer layer, the cornea and the sclera. The middle layer is the vascular layer, also known as the uvea, and it has several functions. Number one, it's going to provide a route for blood vessels and lymphatics that support the eye, so the retina is directly attached to this portion called the choroid.

And it allows for nutrients and oxygen to be delivered to the eye. So that's really a very important part of what this vascular layer does. It also can regulate the amount of light entering the eye, as this part is also part of your iris, which is the colored part of your eye, but also creates the pupil, and it's made of smooth muscle that can constrict and dilate, and so therefore change the opening of the pupil and therefore regulate internet. This layer also secretes and reabsorbs the oculus huma, which is really important to keeping the pressure inside the eye at optimal levels, but also can control the shape of the lens.

You have what's called the ciliary body, which, as we're going to see, is really important to focusing, and altering your focus, basically, if you're looking at something close or something further away. All right, so the vascular layer, again, consists, the first part is the iris. And the iris is made of smooth muscle, which we also refer to as papillary muscles. And these smooth muscles, again, they have, it gives you the color of your eye, but they actually can also contract, change the diameter of the pupil. So smaller diameter or larger, right?

You've got pupils dilated maybe at one point in your life when you're getting vision tested or something like that. And you can see in this image, you have a pupillary dilator muscle, and you also have a pupillary constrictor. constrictor muscle. And the dilator muscle, right, extends radically away from the edge of the pupil and dilates.

You have more light entering. And you can also have a constriction of smooth muscle, that pupil area constrictor muscle, and you can make that opening smaller. So what stimulates the activity of either constriction or dilation, constriction is stimulated by an increase in intensity of light, but also an increase in parasympathetic stimulation. So we have more light coming in, sort of a reflex response is to constrict that to regulate the amount of light coming in, but also So parasympathetic stimulation, right, rest and digest when you have the time, perhaps, when there's less light coming.

On the other side of things, we have dilation. What stimulates dilation? Well, less light, right?

So we have less light. I'm going to dilate more to get more light into the retina so I can see. But then also increased sympathetic stimulation also can cause, right, sympathetic stimulation is fight or flight.

That's when you have the highest. Levels of activity as we talked about in the last chapter and so that's going to lead. So those are two extremes there with the pupil but that's regulated by this middle layer, this vascular layer.

Part of that is also part of this vascular layers as I've said before is what's known as the ciliary body. Ciliary body The smooth muscle, essentially, is attached to the lens via what are called suspensory ligaments. And smooth muscle is kind of like a sphincter muscle, again, kind of like we just talked about with the pupil and the iris, is that the ciliary body can contract or relax, and depending on whether it's contracted or relaxed, it's going to change the tension on those suspensory ligaments that are attached to the lens, and thereby change the shape of the lens.

So the lens actually changes shape. shape altering the refractive power and focusing power so we'll talk about the physiology of that process in greater detail coming up third really important part of this vascular layers let's know is the core and I mentioned this is the actual vascular layer that separates the fibrous layer from the retina and this is where we see oxygen nutrients the way this is essential we know that How detrimental it is when nervous tissue does not have oxygen or nutrients, even just for a very short period of time, you're going to see significant damage to the structure. So, a really important layer to deliver oxygen and nutrients.

And so then the inner layer is the retina. The outer portion called the pigmented and the inner portion called the neural or retina, that's what we'll focus on. And then we have a nice opportunity when you do your dissection to see the retina on the inside of the eye when you slice it open.

Pretty cool experience to see that. So this retinal part contains the visual receptors, and they're called photoreceptors. There are also other associated neurons that helps with the interpretation and conduction and modification of the images.

And so the two primary photoreceptors that we're talking about are rods and cones. You've probably heard of these. Rods are highly sensitive to light, do not discriminate light colors.

So that's what you use, like, for instance, Whereas cones are the ones that provide color vision, light. These cones are densely clustered in what's called the fovea, which is the center of the macula. That's where we want all of our images primarily focused.

Cones, and that's going to give you the highest level. And so you can see your visual axis here goes directly back to the retina. focus in the fovea. Here's a nice image showing you the inner layer of the retina.

See the rhizome region, but then you also have bipolar and ionic attached to that and then you can see the act together to send the impulse nerve to the brain. So as I said, all of these photoreceptors and other ganglionic nerve cells in the retina and other components, all their axons then exit out the back of the eye and the optic nerve. And where that originates exists because there are no photorecepts, only axons leading into the optic nerve.

So as a result, you create this blind spot because light... striking this area because of notice because there are not any photoreceptors in location. So you can do sort of a test, a book that sort of shows how that works.

But here is a really great image where you can see this pigmented portion and the neural part of the retina. And you need to exit the eye so we can get to the brain so you can process images. And so these travel out the back. This look. patient where all those axons are coming together and exiting the eye to go to the brain there are no photoreceptors there right you have photoreceptors over here you have photoreceptors over here but none right here right and so that's the we call the opt so that is what we see in terms of this process happening with sort of this blind spot because there's no photoreceptors at that location.

All right, so, and here's a nice shot inside the eye of the macula and the blind spot at the optic disc. And then there's that test that I was telling you to try. You can try it in the textbook and you'll see one of those spots disappear and that'll demonstrate the presence of the blind spot.

All right, so moving on to the chambers of the eye. The ciliary body and the lens basically divide the eye into a posterior cavity and a smaller anterior cavity. So if you look at this image you can see the posterior cavity is behind the lens and it's much larger.

When you do your dissection, you'll do a cut sort of in that region, right, and you'll be basically dividing it to anterior cavity and posterior cavity. And in the anterior cavity you actually have two chambers, one in front of the iris and one behind the iris called the anterior-posterior chamber. But then of course you have the cornea on top of that. The posterior chamber, we call it the vitreous chamber, which has this gel-like substance that's humor. Here you can also take a moment to appreciate the ciliary body and the dispensary ligaments that attach to the lens.

Like I said, we'll talk about that. So, aqueous humor, as we talked about, is also produced in this region. and it's the fluid that circulates within the eye and helps establish what we call intraocular pressure. It helps retain eye shape and give adequate pressure to the eye.

In the posterior cavity, as I said, there's this vitreous body or gelatinous mass that you're giving your dissection. Hopefully, if the gel is still congealed, it will pop out, and you'll be able to see the gelatinous mass stabilize the eye shape, but also really helps support the retina. That retina needs to always be directly connected to the ciliary body on top of it, right? Or excuse me, the core on top of it.

And so that gelatinous mass sort of presses and pushes up against the wall and keeps the retina directly attached to it. That's really important. A detached retina, which you may have heard of, is something that can obviously cause some... serious issues in terms of all right so the lens we saw the lens is attached to the ciliary body by the suspensory ligaments and as I said part of light passes through the cornea but also passes through the lens and so this lens needs to be clear okay and so the lens always needs to remain this In clear condition, it's filled with crystallins, which help provide this clarity and focusing power to the lens.

And again, the primary function of the lens is to focus that image on the photoreceptors. And it actually has the ability to change shape. Transparency of the lens is essential.

Any alteration of this, if you lose transparency at all, we call that a cataract. You've heard of cataract surgery these days, a laser to surgery really, for the most part, to remove. cloudy or just you know can't see as well through it no need all right so to understand focusing you'd understand the concept of light refraction light basically when it passes from one medium to medium with a different density if that image is going to bend it's going to refract think about putting like say a glass of water you can see the pencil in the glass of water cool right that's good The appearance of that pencil is going to be different, right, because you're looking at it through something of a different medium.

And so that's sort of the concept you have with vision, right? It's bent when it passes from one medium to a medium of a different density. And as we know, light, to get to our retina, has to pass through the cornea as well as the lens.

So those two things are what are providing the refraction so that it focuses directly on the retina. The array is not, the light is not. Directly, perfectly focused on the retina, then the image is going to be blurry, right? And you're going to use a third layer of the front.

Cornea and the lens are not getting it done. That's why people look up. or contacts right to sort of provide that third level of refraction so the image is bent and hits the retina and direct okay so focusing is done at the lens right and as I said it's held in place by the sensory suspensory ligaments of the ciliary body okay the smooth muscle in the ciliary body act like a sphincter and so it can either contract or relax and if it contracts the ciliary body is moving closer to the lens closer to the lens, the ligaments will be a little more lax and therefore the lens is going to be rounder or more spherical. This rounder, more spherical shape increases the refractive power and allows you to focus things that are much closer, okay?

When something is further away, the lens needs to flatten, decrease the refractive power so you can focus on something that's further out. So sensory ligament, excuse me, when the ciliary body relaxes, it pulls away from the lens, that's going to... tighten the ligaments a little bit, and then pull on the lens, and the lens will stretch out and there you have this focusing power based on what the ciliary body is doing.

So here you can see the ciliary body, here's the lens, and you can see these suspensory ligaments that are attached. The ciliary body moves closer, which is going to relax the ligaments, or it's going to move away, which is going to cause more tension. When it moves away, it's going to flatten. When it moves closer, it's going to become more sparse.

And that's what changes this, we call this accommodation of the lens, changes this ability to focus on whether we're looking at something closer in our field of view or something that's much further. And so here you can see with a regular lens, it allows you to look at close. The ciliary muscle contracts, it moves closer, and the lens becomes more spherical and focuses it rather than putting as much focus on the lens. further away, right? The ciliary muscle relaxes and pulls away from the lens, flattening it out, and then also focusing.

So, clarity of vision, right? Being able to see something clear. As I said, if you cannot, if something's not focused directly on the retina, you're not going to see it very well, right?

And so you've heard of like 20-20 vision, right? That's basically a comparison, right? It's someone who has Your vision compared with someone who has quote-unquote normal vision, right?

And you can see, you know, details like oftentimes optometrists will use a board of letters and numbers. You guys have all seen that before, right? And at 20 feet, you can see what someone with normal vision can also see at 20 feet.

So you guys are at the same distance, you know it's good, and we call that 20-20. Worse than if your vision is worse than someone with quote-unquote normal vision. Then it can be 20-30, 20-40, 20-50, etc.

This means that what you need to see at 20 feet, someone with really normal vision can see much further, right? So that's what that means. And so part of the more common types of accommodation that occur, things like myopia, which is nearsightedness, right? This is being able to see things, obviously, pretty well. close range but things that are further out are going to be harder to see and a lot of it has to do just with the architecture of the eye inside the skull right if the eyeball is too deep or the resting curvature of the lens is too great it's not going to hit the retina perfectly right region at close range is typically normal because the lens can can accommodate for that but when you get further away the lens can't sort of make up the difference Third layer of refraction here, myopia is corrected with a divergent concave lens.

It's going to adjust the focus. Hyperopia, which is farsightedness, another fairly common type of sort of issue with vision, right? Accommodation issue.

The eyeball can be too shallow or the lens too flat. Again, you're going to sort of overshoot the retina, and it's not going to be focused directly. oftentimes older individuals become farsighted as their lens loses elasticity and so it's not able to really be focused properly.

So again a converging lens here is going to help adjust that focus so it hits through. Probably heard of LASIK or PRK other types of keratectomy surgeries that basically try to repair this issue, right, to correct this instead of having to use glasses. It sort of replaces glasses.

like in basic for instance they're actually reshaping the cornea right and trying to get it so that it has the right amount of refraction to get it focused directly on the retina so that's an option if you don't like wearing glasses and contacts and things like that you can have surgical care. So that's it for the eye what about the ear the ear is You know, pretty straightforward in terms of its structure. We have nice models in lab for the ear.

You'll be able to see all these structures pretty simply. So we'll go over the structures real quick, talk about a few clinical applications, and then look at the physiology of the ear. So, the ear, the structure of the ear is in three components, external, middle, and inner ear. The external is what you see on the outside flap that sits on your ear.

Also called the auricle or pinna, the direct sound waves funnels them into the middle ear. The middle ear is the airfield chamber that actually connects these sound waves and initiates the process of turning a mechanical or physical stimulus of sound waves into an electrical impulse. And then ultimately, the sensory organ for hearing an equilibrium is in the inner ear, and that's where the impulse will be created and sent on the vestibulocochlear nerve, cranial nerve number eight, which I know you guys are currently learning. So here you can see all those structures.

You have the external ear with the auricle and the external acoustic meatus. You have the middle ear, which has the auditory ossicles and begins with the tympanic membrane. And then you have the inner ear, which again has the organ cochlea, which is responsible for hearing, but then it also has the vestibule and the semicircular canal. which are all right so the external ear also referred to as the auricle or pinup again basically is providing directional sensitivity sensitivity funneling sound waves deeper into our ear into the external acoustic natus also providing some protection to the opening of that pathway the external Acoustic natives ends of the tympanic membrane, which is otherwise known as your eardrum. And this tympanic membrane is really important.

It's within a semi-transparent sheet. It basically responds to those initial sound waves that arrive in your ear and will then be conducted further deep. Also in the external ear, we have ceruminous glands. They secrete more of a waxing material.

Obviously, you know, as ear wax, I'll call it cerumin. And that's really, you know, there's a purpose to it, right? Just keep foreign objects out of the tympanic membrane and slow, prevent or slow the growth of microorganisms or bacteria, things like that, trying to protect the ear, okay? So that's the external ear. The middle ear is also referred to as the tympanic cavity and basically includes what's called the malleus, incus, and stapes.

It also has an auditory air tube, as I mentioned, which communicates with the nasopharynx. and also is a pressurized cavity. The tympanic, the three auditory ossicles, the malleus, incus, and stapes, are all attached to the tympanic membrane. And so when that tympanic membrane vibrates, these guys are attached to the tympanic membrane and create sort of a kinetic chain of movement. In other words, when the tympanic membrane vibrates, malleus will then vibrate, which will stimulate the incus, which will then stimulate the...

the stapes and then that will create a pressure wave inside the organ, the sensory organ, which we'll talk about in a minute. So that's looking inside the ear. The vibration of the tympanic membrane, again, is really the first step in this process. It converts those sound waves into actual mechanical movement or distortion of those auditory obstacles.

and then those auditory oscillators will conduct those vibrations. Now you've probably heard of pediatric ear tubes, right? Based on the architecture of the growing child, oftentimes kids, when they get cold, can get ear infections very easily because fluid can build up, and when you have fluid, it can put a lot of pressure on the tympanic membrane, and basically there's no place for the fluid to escape, and as a result, not only can it be painful, but bacteria can multiply and develop and treat. When you have an ear infection, well typically antibiotics, right? You get a bacterial infection, use an antibiotic to treat it.

And that's fine if you get one or two or a couple in your life no big deal but if it's as often times the case with a lot of kids this happens over and over and over and over again every time they get an ear infection you don't want to keep treating the child with antibiotics right you want to hopefully come up with another method of treating that's another way of relieving these symptoms and so that's what pediatric ear tubes do right they basically create a conduit or a pathway for any fluid that might get trapped in that middle ear to escape And so I speak from personal experience. My kids have this done. Basically, the physician goes in and puts a small incision on the tympanic membrane, pops an actual little tube in there.

It's like a little colored tube that's then going to allow fluid to escape, not allow pressure to build up, and not allow bacteria to form. And hopefully that can be used instead of having to treat the kid with antibiotics. That is a pediatric ear tube. So then on to the inner ear. The inner ear has this structure that has this bony labyrinth that surrounds and protects the membranous labyrinth on the inside.

And inside that, you have a fluid called an endolymph. And basically, the stapes attaches at this structure at the oval window, and that puts a vibration and changes, distorts the fluid of the endolymph, and that's what's ultimately going to stimulate the nerve ending, which is going to send sound waves out. or excuse me, which is a depolarization of the nerve ending and send the impulse, turn it into an electrical impulse, right? That's the trick.

That's what the ear has to do. That's physical stimulus, which is sound waves of pressure, and convert that into an electrical stimulus so that the brain. So anyway, so this thing is divided into three parts.

You have what's called the vestibule, the semicircular canals, and the cochlea. And here you can see, here's the cochlea. That's the hearing part.

Here's the vestibule, and here are the semicircular, okay? So they're all responsible for something a little bit different. If you take a cross-section through, you can see how this is organized. This is a cross-section through the semicircular canal, for instance, and you can see you have the bony labyrinth on the outside, and on the inside you have a membranous labyrinth. Inside those two spaces, you have a paralymp, which is beneath the bony labyrinth, and then you have an endolymph, which is deep inside the membranous.

That endolymph is ultimately where we're going to see distortion that's going to stimulate the vestibule. It's responsible for sensations of gravity and linear acceleration. Semicircular canals are stimulated more by rotation of the head, but these two components are the ones that are responsible for equilibrium and balance.

Cochlea is the part that's responsible for providing our sense of hearing. And so we'll look at that. Alright, so the oval window, you have these two structures of the round window and the oval window. The oval window is what's attached to the stapes, and the stapes is ultimately the last thing that distorts, which is going to establish a pressure wave inside this. So, hearing then is provided by this cochlea.

The cochlea has nerve cells in them. Those that are responsible for that are what are called hair cells. Hair cells are in what's called the organ of Corti and has a bacillus membrane on top, a tectoral membrane on the bottom, and if the pressure wave passes through this endolymph, it's going to stimulate these hair cells, causing vibrations of the bacillus membrane, and that's going to stimulate these receptors.

So here's a nice image of... For instance, a hair cell, right? You can see the stereocilia on top of those, the hair cell.

So hearing basically works as these auditory ossicles vibrate and change. It's putting a pressure wave into the paralymp of the cochlea, right? And so frequency of sound is determined by which part of the cochlear duct is stimulated and intensity.

determines how much of the hair cells are actually stimulated. So to understand how this process works, the actual physiology of hearing, we need to understand a little bit about the sound, right? And without getting into too much detail, sound consists of what are called waves of pressure.

A pressure wave is essentially an area where you have air molecules together, and then right next to them you have it further apart. Very close bunch of air molecules together, another area closer to part. So those are wavelengths. It's a distance between each one of these waves. frequency is how often they pass over a fixed reference point in a given time.

So these waves of pressure arrive and are produced when, you know, sound is produced, right? That's when sound is a physical process. So for instance, my speaking right now, my vocal cords are vibrating and producing those sound waves, or if you strum a stringed instrument, right? Think about strumming a guitar, you can see those strings vibrating and they're distorting and creating these pressure waves.

that can arrive at our tympanic membrane ultimately in that wave of distortion. So sound is produced by energy as I just described. The vibration of vocal cords or a tuning fork or a stringed instrument, right, is producing these sounds.

And the more flexible an object is, the easier it will respond to those pressures. So tympanic membrane has to be pretty flexible. It's like pretty thin types of strings. structure needs to be very sensitive to the sound pressure so I can stimulate.

And so here shows sort of how that works, right? Like a tuning fork, you guys can place any one of those before you hit it and you can see it vibrating, but you can also, it's producing these air molecules, these sound waves, and these sound waves are then tunneled into the ear and ultimately arrive at the tympanic. Okay, and so this, these next six steps show that exact process.

In the first step, those sound waves are produced. In any way, right, speaking, vibration of stringed instruments, other types of methods that produce these sound waves, right, they're ultimately going to arrive at the tympanic membrane. Once the tympanic membrane vibrates, that causes then displacement of the auditory ossicles. So tympanic membrane vibrates, the malleus then moves, that causes the incus to move, that causes the stapus to move. So that sort of is like a kinetic chain of motion.

And the stapes, as we said, is attached at the oval window, and it creates movement of the stapes, establishes a pressure wave in the paralymp, which will ultimately lead down to distorting the bacillus membrane, which will ultimately cause vibration of the hair cell against the pectoral membrane, and that ultimately will lead to stimulation of the neuron ending, the cochlear branch of cranial nerve number eight, also known as the cranial nerve. Here you can see that in these images. So make sure you have a good understanding of those six steps and see how you're essentially the body or this organ, this cochlea, is converting pressure waves into actual intellectual.

And to further understand that, there's this story I heard on NPR, and actually I studied this molecule a little bit in grad school. This is a... Triphae-1 protein is a molecule that actually opens when a certain sound wave sweeps over that channel. And so, again, it's a mechanically regulated channel. Remember we talked about channels that need to open to allow for depolarization to occur, to allow ions to rush into the cell?

Okay, this one is going to open at a mechanical stimulus. And so that's what happens, right? Once that mechanical stimulus arrives, it opens these mechanically regulated channels, allowing the moves. Electrically charged ions pass in the flow into the hair cell and that ultimately converts it then into an electrical impulse that can be understood by them.

Right? That's really the trick, right? Converting a mechanical stimulus into an electrical impulse.

And this is where it happens. So if you click on the link, you'll probably have to pull up the actual slide itself and put it in PowerPoint in presentation mode. You should be able to click on that and go to the link. And it's just like, you know, a five-minute story. I think it will help pull together all of these things we're talking about.

And so here are some images of a hair cell bundle. These hair cells are what you're able to detect but also amplify sound waves. And that trip A1 sits at the tips of those structures and allows for the impulse to be created as an electrical.

So... Hearing range from softest to loudest, right, really is a huge increase. We never really used our full potential.

Young children typically obviously have the greatest range, and as we get older, we really start to see diminished hearing capability. Basically, it's just a result of damage over time, right? We lose hair cells, right? Over decades and decades and decades of hearing all the time, we're going to lose some hair cells.

And so... The tympanic membrane also can be less flexible, so it's not going to respond as easily to those sound waves. Articulations between the auditory ossicles will stiffen. You might see ossification at the round window, which is going to diminish how things can be transferred into the paralymp. So all these things can contribute to diminishing hearing as we accept the pretty typical symptom of aging.

Alright, so that's it for the eye and the ear. Again, this will coordinate nicely with what we're doing in lab. Our last chapter for the semester will be the endocrine.

Transcript for:Understanding Eye and Ear Anatomy

Transcript for:
Understanding Eye and Ear Anatomy