Unlike the nose, tongue, and eye, the ear actually handles two of our special senses. It handles obviously hearing, but it also handles our equilibrium. So let's first talk about the anatomy of the ear, and then we will split up and separately discuss equilibrium and hearing.
So the ear, as I mentioned, is responsible for both of these things, and I know that everybody knows the word hearing, but when we say hearing, we very specifically mean being able to both detect sound waves that travel through the air or water, but also being able to interpret those sound waves and know what it is, know that someone is speaking. know that's the sound of a car or a door or a book falling to the floor. So both detecting and sounds and interpreting those sounds are aspects of hearing.
Now for equilibrium, this is basically your sense of balance, right? And so the way that equilibrium works is in the ear, a part of the ear is dedicated to sort of knowing the position of your head in space, both, you know, if you're standing straight up or sitting up or laying down. or your head's tilted to one side or the other, or you're moving, right?
You're moving forwards, backwards, left, right. You're spinning in a circle. All of these is related to equilibrium, right? Because we are detecting the position of head in space, your head in space, and if it's moving or not.
So the basic mechanism, the basic type of cell in the ear that is dedicated to detecting these stimuli are what we call hair cells. So we have both hair cells are able to detect both equilibrium and hearing, but... but in different parts of the ear. It's the same basic type of cell, though, in different areas that are responsible for this detection of these stimuli. So once hair cells get activated, whether it's the hair cells that are monitoring your equilibrium or monitoring your hearing, they allow for the creation of action potentials so that neurons can send action potentials towards the brain to process this incoming information.
So the ear is divided up into three general regions, and then from there each region is obviously made of different structures. So let's start with these three anatomical regions. The first region is what we call the external ear, and followed by the middle ear because guess what, it's in the middle.
And then we have the internal ear after that. So the function of the external ear is to be able to collect sound waves and then direct them farther in. towards that middle ear right here.
Now the middle ear receives those sound waves that's collected by the external ear out here and then its job is to direct that sound wave information in to the internal ear. So the internal ear is going to receive those sound wave type of vibrations from the external than the middle ear. It's going to collect those Sense those and then transmit that that hearing sound wave information towards the brain The internal ear is also responsible for monitoring our sense of equilibrium and unlike hearing You know the sound waves have to go through the external middle and then the internal ear Equilibrium is all handled and self-contained within the internal ear itself and then it will then transmit that information again to the brain Let's take a closer look at the external ear. Alright, another name for the external ear is the outer ear.
Guess what? It's on the outside. And again, it is able to collect sound waves, sort of like a radar dish, right, and then transmit them, concentrate them, transmit them to the middle ear. This part here, This part of your external ear is referred to as the auricle.
Right? This is the auricle. And from the auricle, then we go farther deep or into the body. And then this little canal here is referred to as the external acoustic meatus. So the function of the auricle there is again sort of like a radar dish.
It can will collect sound waves from a wider area and then kind of funnel them into that external acoustic meatus. The shape of the oracle also allows us to sort of automatically be able to determine which direction the sound waves are coming from. The external acoustic meatus really it's there mainly to just send those sound waves on to the middle ear.
It does have a couple of other names which are commonly, it's commonly referred to as, it's also referred to as the auditory canal or the ear canal. In everyday language people usually call the external acoustic meatus your ear canal. Now when we take a look here at the ear canal, we want to be able to kind of filter out the debris prevent things like insects and spiders from getting farther in and getting stuck in our ear.
So that external acoustic meatus has a lot of hair in there. That's your ear hair. And the ear hair there is a decent filter, right?
So all that ear hair makes it sort of difficult for debris to go too far in. They sort of get filtered out. Also, if you get material or something like maybe an insect that's trying to get into your ear.
The insect pushes on the ear hair and your body is able to sense pushing of a hair, right? So you can feel that when a hair gets bent. So, you know, the insect gets into your ear, pushes on an ear hair. It sends a signal right to your brain and you almost, you know, automatically put your hand to your ear to try to get that thing out without even really knowing what's going on.
We also have earwax. So earwax is known as cerumen. And that cerumen, or earwax, is produced by glands called ceruminous glands in the external acoustic meatus. So that wax does a pretty good job. It's pretty sticky, right?
So it's good at trying to trap insects and other types of debris that might filter in. There can be a problem with the cerumen. You see the picture on the left here, right? If it gets too thick or maybe you stick a Q-tip in your ear canal, you sort of compact and compress.
press the earwax and it can get in the way of sound waves passing through and it can make it harder to hear. So the picture on the right here, right, this is a nice clear clean view into going into that middle ear. So as I mentioned the cerumen there is pretty sticky stuff.
It helps kind of trap debris and insects, things of that nature. Any types of microbes like bacteria that start to try to get into the body or you get into that ear canal, you know, they can stick to the cerumen. They're also, because it's so thick, it's really difficult for microbes like bacteria to be able to divide and proliferate within that cerumen, that earwax stuff.
So it does slow down the rate of growth. All right, next up is the middle ear. So the middle ear is also referred to as your tympanic cavity. Again, it's going to collect those sound waves coming from the outer portion of the ear and direct it towards the the internal ear the inner portion of the ear. So let's take a look at these different structures of the middle ear.
So first of all, we have the tympanic membrane right here, right? Tympanic membrane. Tympanic membrane is also referred to as your eardrum and so sound waves that are coming in the sound waves hit this tympanic membrane and cause this tympanic membrane to oscillate or vibrate back and forth. So every time it gets hit by a sound wave it pushes in and then it springs right back out like a trampoline and then gets by another sound wave and another sound wave.
So back and forth it sort of oscillates or vibrates. Also here in this portion of the ear we have what we call your auditory ossicles. These are like your three little bones inside your ear, the auditory ossicles. So auditory ossicles, each one has a different name.
The first one, the first one up, this is the one that articulates or connects to that tympanic membrane. This auditory ossicle is called the malleus, malleus for mallet. The next one up is the incus. All right, all right. So malleus like mallet or hammer.
Incus means anvil. You can imagine possibly a blacksmith hammer hitting metal on an anvil. And then after that, the last one is the stapes. Stapes means stirrup because the shape of it is like the stirrup of a saddle. So malleus, incus, stapes.
Hammer, anvil, stirrup. All right. So the idea basically is. when sound waves are hitting that tympanic membrane and it oscillates or vibrates back and forth because it's connected to these bones, the bones also move back and forth. They're all connected with each other. Ultimately, the stapes here, if I were to lift up the stapes, underneath the stapes is not bone, it's a little thin membrane, and because the stapes is wiggling back and forth it's pushing on this little this little thin membrane here that we call the oval window, and that creates little waves in the fluid on the other side of the oval window.
and the little fluid waves, that's how we translate sound waves into fluid waves, and those fluid waves are going to go to the internal ear and help us help those hair cells detect sound. We have a couple of very small muscles here in this tympanic cavity, and you don't need to know the names of the muscles individually, but these two muscles that you see here, what they can do is if the sound waves has a really big amplitude, if it's very, very loud, all right, we don't want the tympanic membrane in these auditory ossicles to vibrate so much that they rip apart, they tear, they cause damage. So if it's for really loud sounds, these muscles will contract more.
And when they contract more, they pull on the auditory ossicles and prevent them from moving too much where it would cause damage in that internal ear. However, if the sounds are very quiet entering the ear, then the muscles can relax and allow those auditory ossicles to move enough to move more so we can actually hear quiet sounds. Alright, so after we move past this portion of the tympanic cavity, okay, and this is really there to help transmit the sound wave information.
to the internal ear. We have this other section right here. This little tube here.
This little tube is called the auditory tube. And the auditory tube has a couple of other names. It's also known as the eustachian tube or the pharyngeal tympanic tube. All three names get used.
Auditory tube, eustachian tube, pharyngeal tympanic tube. What this does is it leads to sort of the upper portion of the back of your throat. All right, so the upper portion of the back of your throat, we call it the nasopharynx.
I will show you a picture of that in just a minute. So the function of this auditory tube here is because it leads into like the upper portion of your throat, more or less, it's going to make sure that the pressure doesn't build up too much in this middle portion of the ear. So to sort of help equalize the pressure, let's say.
Without the auditory tube, or if the auditory tube gets plugged up when you're sick, The pressure can't be equalized and the pressure builds up inside here and it becomes painful and difficult to hear. All right, so we need to be able to sort of let the pressure out inside here and that pressure gets let out if it tries to build up through this auditory tube. So let me show you what I was talking about when I mentioned the nasopharynx, right?
So nose, nasal cavity, sort of this part right here, this is all your pharynx, all right, pharynx kind of like throat. But we have the upper portion, the middle portion, and the lower portion of your pharynx. So this upper portion up here, this is your nasopharynx, the part that's close to your nose.
And that auditory tube just leads directly into that nasopharynx so the pressure doesn't build up in there. However, some people can get a middle ear infection. This is fairly common in children.
So if you look back up here, This tympanic membrane really seals off the middle ear from the outside, yet you can still get ear infections. Usually an ear infection is a middle ear infection because of this auditory tube. We need it to equalize the pressure, but because it's connected back into that nasopharynx, any types of germs, bacteria, whatever, they can move up from the nasopharynx through the auditory tube.
and they can get into the middle ear and cause one of these very common middle ear infections. Middle ear infections are referred to as otitis media. Media means middle, alright? Oto means sound or ear, and itis is inflammation. So inflammation of the middle ear, otitis media.
This takes us to the internal ear. So the internal ear People also call it the inner ear, so not very science-y or Latinized names for it, but internal ear, inner ear, this is what everybody calls it. So when we look at the inner ear... It is this boxed off section right here. A lot of what occupies the space in this inner ear is this snail looking structure that you see here.
This stuff here. So this structure within the inner ear is what we call a labyrinth. A labyrinth. A labyrinth is like a maze with lots of turns and twists. And so in this labyrinth here, there's lots of different routes.
the material can travel through. So this structure here is what we refer to as the labyrinth. So let's, the labyrinth is where we can sort of collect the information both for hearing and equilibrium both.
It's handled by the labyrinth. It will collect hearing and equilibrium information in different parts of it and then convert that information over into action potentials and that gets transmitted to the brain to be perceived. Alright, so if we were to take a cross section of the labyrinth. So what do I mean by cross section? Remember your anatomy terms?
So if I take this part of the labyrinth and I slice right through it and we look on the inside, this is what we're looking at here. So we have these different layers and different kinds of fluids in these different parts here. So the labyrinth, I think of the labyrinth as a tube within a tube.
The outer portion of the labyrinth. is made of bone, so we call that the bony labyrinth. This other wall or partition is not made of bone, it's a soft flexible membrane, so we call it the membranous labyrinth. And then we have material between the bony and membranous labyrinths, and then we have material inside surrounded by the membranous labyrinth.
This material is fluid. So the fluid between the bony and membranous labyrinths is called perilymph. The fluid surrounded that's inside of the membranous labyrinth is what's known as endolymph. Endo means within.
So it's the fluid that's the farthest in. Inside that membranous labyrinth is what we refer to as endolymph. And then the fluid outside, around the membranous labyrinth, is perilymph.
Peri means around. The Boney Labyrinth is divided up into different sections. So the sections of the Boney Labyrinth include this portion right here. This is called the vestibule.
You see all this stuff here, right? This, I'm sort of circling it. This is the vestibule. And then we have these three passageways.
These three passageways are referred to as the semicircular canals. Again, this is the part of the bony labyrinth, the outer hard bony part. Semicircular canals.
Semi means half, so these are half circles, semicircular canals. And then we have this part here called the cochlea. Cochlea means snail, because it looks like a snail shell. This is the cochlea, this part of the bony labyrinth that spirals around.
The membranous labyrinth all right, is divided up into its own sections that are similar because they're inside of the bony labyrinth. So here's the membranous labyrinth. We have the saccule and utricle. So this part right here, okay, this part's called the the utricle and this part right here is called the saccule.
Utrical, saccule. The part of the membranous labyrinth that runs within the semicircular canals are called semicircular ducts, and the part of the membranous labyrinth that runs inside the cochlea, that is called the cochlear duct. So both the utricle and the saccule These are the areas that contain receptors to sense your equilibrium, your position of head in space and if it's moving or not. So equilibrium is handled partially in here.
We find even more receptors for equilibrium also in the semicircular area, semicircular ducts and canals. The cochlea is dedicated to containing receptors for hearing. So those hearing or sound wave sensing receptors are found in this cochlear duct, that part of the cochlea. So I already mentioned the oval window, the stapes. If I were to...
lift up this bony part here, the stapes, there would be a pliable soft membrane on the underside of here. That's the oval window. And so when these auditory ossicles are vibrating back and forth, the bottom of the stapes presses on that little membrane because we now know that there's fluid in here.
Every time the stapes moves back and forth, it presses on the oval window and the oval window presses on the fluid and we create these little waves that go through the fluid. Now, The problem is this entire area here in the labyrinth, it's all mostly bone. And bone does not bend and flex.
So if we want to press fluid and make fluid waves go through the labyrinth, then every time we push in, in the oval window, we need another area to give way to push out. So we have another little portion of membrane right here that is not bone. This one is called the round window.
And so the round window again, like the oval window, this is not bone, this is a soft, pliable, flexible membrane, and it allows the fluid waves to travel through the cochlea. So every time we press in, right, that presses on the fluid and the fluid creates a, there's a wave created by the fluid, but that fluid has to go somewhere. So every time this presses in in the oval window, the round window flexes out, the fluid pushes it out. So pushes in, this pushes out. When this comes back out, this comes back in so that we're allowed to push the fluid inside here to create these.
fluid waves for sound. Okay, that is the basic anatomy of the ear.