episode37

037 How Sound is Transferred to the Inner Ear

In this episode, Leslie talks about how sound is transferred to the inner ear. Because there is fluid inside the cochlea, impedance matching has to take place for the vibration in the fluid to accurately represent the sound that you are hearing.

Watch this video to learn how this process works.

Transcript of Today’s Episode

Hello, and welcome to another episode of Interactive Biology TV where we’re making Biology fun! My name is Leslie Samuel and in this episode, episode 37, I’m going to talk about how sound is transferred to the inner ear.

Let’s see and visit an animation that we looked at in the last episode. We looked at this animation that showed how, when you hear something, there are sound waves that are entering into the ear, and those sound waves come in contact with the eardrum, the tympanic membrane.

The tympanic membrane vibrates back and forth and that vibration is transferred to the three bony ossicles, the malleus, incus, and stapes. It’s connected to the cochlea, and that’s going to cause something to happen in the cochlea that’s going to cause a signal to go via the auditory nerve to the brain. That is how we hear.

Now, what we’re going to talk about is what happens in the process of moving that sound, transferring that sound to the inner ear. Later on, we’re going to look at what happens inside the cochlea.

So, let’s get into some more detail. Here, we’re looking at a structure of the ear. We have the outer ear, so, I’m going to refer to this part, up until the tympanic membrane or the eardrum as the outer ear. Then, we have this section here with the malleus, incus, and stapes, the Eustachian tube. This is called the middle ear (forgive my writing there).

Then we have the with cochlea, the semicircular canals, and the nerves and so on, that’s called the inner ear. We’re going to be talking about the process of sound being transferred from the outer and middle ear to the inner ear.

Now, here’s the deal, in the external auditory canal, that’s in here, we have air. In the Eustachian tube that’s in here, we have air once again. However, inside the cochlea, we don’t have air. We actually have fluid. Now, because of that, it’s going to be harder to get the fluid inside the cochlea to vibrate than it is to get the air inside the middle ear and inside the outer ear to vibrate. Think about it this way. if you’re running in air, which, when you’re running you’re usually running in air, that is not as hard as if you’re trying to run in water.

So, in order for us to have the same strength of signal out here and in the fluid inside the cochlea, something needs to happen and that process is called impedance matching. Impedance is basically resistance and we’re trying to match the amount of resistance here to the amount of resistance here. We want the same signal in the fluid in the cochlea that we have in the air inside the outer ear.

This can sound a little confusing because sometimes, I’m referring to “air,” and sometimes I’m referring to the “ear.” But, what we’re basically saying is, when the signal comes here and causes the tympanic membrane to vibrate, we want the signal to be transferred with the same amount of strength to that fluid inside the cochlea. So, we have to go through this process of impedance matching.

There are two ways that impedance matching is accomplished. Let’s look at the first way. Here we have the three bony ossicles, the malleus, the incus, and the stapes that‘s attached to the oval window here. Now, I’m going to draw the malleus, incus, and stapes over here in a very simple way. So, let’s say this is the malleus, this is the incus and, this is the stapes. Now, it makes sense that if the malleus vibrates back and forth, so let’s say it’s going back and forth, that’s going to cause the incus to vibrate back and forth, and then that’s going to cause the stapes also to vibrate back and forth.

However, because of the way these are connected and the hinges that we have between these three bones, I’m not necessarily going to get the same amount of movement here as I get here. I can orchestrate this in a way that when this moves, these are connected so that these will move even more than this is moving. It will move a greater distance. And this is exactly how the malleus, incus, and stapes are set up so that we have a movement ratio of 1.3 to 1. In other words, and I’m going to take a random number, if this moves 1 micrometer back and forth, this is going to move 1.3 micrometers back and forth.

So, we’re going to get more movement here than we are getting here. And that is going to cause increased pressure on the oval window. So, we’re going to have a certain amount of pressure here, but the amount of pressure we get on that oval window is going to be greater. This is exactly what you want because you want to move the fluid inside the cochlea the same amount, you want the same amount of vibration that we have inside the tympanic membrane so that you can send an accurate signal to the brain via the cochlear nerve, or another name for this is the auditory nerve. So, the first way to compensate for the fact that we have fluid in here is by having a movement ratio of 1.3 to 1 between the stapes and the malleus. That is the first way.

Now, let’s talk about the second way. Here, once again, we have the tympanic membrane or the eardrum, and here, we have the oval window. Now, you will notice something about the size of the two. The tympanic membrane is larger than the oval window. To be more specific, it’s approximately 18.6 times larger. Now, why is this significant? I’m glad you asked. Let’s take a very graphic example. Let’s say we have a surface here and we’re going to see that that surface is your leg. On top of that leg, we’re going to put a block, let’s say we have a brick. What happens if someone comes along and decides they want to punch that brick with a certain amount of force. They punch that brick, it’s on top of your leg, and you might say, “Ow!” because it might hurt. I hope that makes sense.

Now, let’s take a different situation where once again, we have your leg but, instead of having a brick, we have, brace yourselves, a needle! I know what you’re thinking already. This is kind of crazy. Well, it is! Let’s say a person comes by, and they do the same exact thing. They come by and they punch that needle that’s right on the surface of your leg. This is the same amount of force that they punch over here. Are you going to notice the difference in the amount of pressure? I am betting that you will! This is going to hurt much more. Most likely if they’re punching, the needle is going to go into your leg and you are going to scream.

I don’t care how strong you are, you are going to scream. The same amount of force as here however, here you have an increased amount of pressure because you have a smaller area. So, I’m going to write here, “smaller area.” This is not the situation that you want to find yourself in. However, in some cases, it can be a good thing. Here, where we have the tympanic membrane being 18.6 times larger than the oval window, what that is going to do is cause an increased amount of pressure due to this vibration. And, what’s that going to do? Well, we said, we have fluid inside the cochlea, air inside the Eustachian tube and inside the outer ear and we want to match the vibration out here which is easy, with the vibration in here which is harder because of the fluid.

So, once again, the two ways that impedance matching is accomplished so that we can get an accurate amount of vibration inside the cochlea is by having a ratio of 1.3 to 1 between the malleus and the stapes; and by having the tympanic membrane 18.6 times larger than the oval window. That’s going to cause the fluid inside the cochlea to vibrate in a way that matches the vibration that’s happening out here. Then, that causes a signal that goes via the auditory nerve to the brain.

In the next video, I’m going to talk more about what happens inside the cochlea. So, make sure to check that one out. That’s it for this video. If you have any questions, as usual, feel free to ask them in the comments section below and I’ll be happy to respond to your questions. Who knows? I might even make a video to answer your specific question. Also, you can always visit the website at Interactive-Biology.com for more Biology videos and other resources. That’s it for now. I’ll see you on the next one.

194 comments
Zandi
Zandi

I am a speech therapy student and this honestly helped me pass! Thanks so much!

Giselle
Giselle

Leslie, you are better than carrot cake being served on vacation in the Bahamas! Thank you for going step by step and being clear. If only all teachers could teach the way you do. Thank you, again!!!

muslimah girl
muslimah girl

great job! i am a med student and i couldnt understand the mecanism of hearing till now! :) actually it helped my friends too coz we were totally lost(the least to say) so thank u :)

Seneca
Seneca

I don't think I could have passed my Hearing Science class without you! Thank you so much!

M. Cato
M. Cato

Do you take donations?

Hilary Smith
Hilary Smith

I am trying to understand better how sound waves are transferred for A&P. Looking for a video or web page that list in order the structures sound waves pass through as they enter the ear and make their way to the brain for processing ending at cranial nerve. Do you have anything like that? I am just trying to get an understanding before my test next week. Thank you!!!

MoonMaisie
MoonMaisie

Maleus, incus and stapes are latin forms of the same terms. The displacement of the fluid (you're talking about perilymph) allows movement of the basilar membrane which is crucial for moving the hair cells, signalling the location of displacement of the basilar membrane, and so signalling pitch. (there are actually 2 different types of fluid, perilymph and endolymph, which have different dissolved ion contents in order to generate electrical signals in the hair cells) Hope this helps!

Eoin Craig
Eoin Craig

I'm a first year medical student. This helped me learn about impedance matching easily. I never got it until now. thanks a million.

Veena Bhaskar
Veena Bhaskar

Hi.I am from India...i teach Biology to high school students.This video is very informative and amazingly done.I am going to use it for my teaching...thanks...

Kristin Betancourt
Kristin Betancourt

You channel is soo helpful! You describe everything very well and make it seem so simple. I always refer to your videos first before any others!

Kristin Betancourt
Kristin Betancourt

You channel is soo helpful! You describe everything very well and make it seem so simple. I always refer to your videos first before any others!

Cork Hicks
Cork Hicks

Thank you. This was informative and easy to understand. It was useful for the context that I'm interested in. My granddaughter has EVA and I'm trying to understand why the enlarged endolymphatic duct and sac affect the (1) ionic composition and (2) volume such that homeostasis is disrupted to the extent it functions abnormally or not at all. Just because it is bigger why the negative effect?

Brittany Henderson
Brittany Henderson

by the way this drs name is dr. jon jonikas at the va hospital in mt. vernon...he says nothing in wrong with my knee but at nite i cant sleep ,,,ev ery nite...scream and cry from the pain and he wont give me pain medicine cuz i am dizzy but he doesnt know why i am dizzy....i think its menieres from the metal...c below other post

Brittany Henderson
Brittany Henderson

my doctor washed my external ear for metal when the radiologist said the metal was in my inner auditory canal.....i pass out , have vertigo,,,ant walk straight...but i can sit and look normal he said....what do you think will happen to me? charleneroray@yahoo.com

Ashwin Kumar
Ashwin Kumar

No body forced you to believe or not to, if you think god does not exist, so be it, the last thing i want is that people like you to comment on my statement.

Esther L
Esther L

i learnt the names differently :P are those bones also called as hammer, anvil and stirrup? O.o it's kind of hard to understand with different names... and just a question, why do we have that fluid inside that cochlea? :D

Alexander Christy
Alexander Christy

Are you implying that the human ear is irreducibly complex? You're sorely mistaken if so. Also, if humans are made in the image of god, why would we have such inferior ears to "lower" animals, not to mention how easily damaged our hearing is? So, yes we do say god doesn't exist, but that assertion isn't based on such tenuous arguments as yours for his existence, which seem to be seated solely in your own lack of imagination.

studentquestor
studentquestor

The "stapes" bone could also be called "stirrups", right? I've grown up using the latter.

studentquestor
studentquestor

I think so. Maybe you could check out the next video where Leslie will explain the cochlear fluid.

studentquestor
studentquestor

I agree! Intelligent design really does play here. The different parts of our body seem to have specific functions, and yet they are in harmony.

studentquestor
studentquestor

You could look up on proper ways to cite a webpage. Of course, you need to provide the link, and include Leslie Samuel in the citation.

Ashwin Kumar
Ashwin Kumar

Just as if it was designed by some one, and they say god does not exist.

Jacqueline Snow
Jacqueline Snow

Wow! i love the way you explained this. Thank you so much for explaining it to us in toddler language. It is all so clear now!

Aysha Akter
Aysha Akter

very good explanation but that example of needle going inside the leg was really crazy...guess , thts how doctors talk...!

Kat Plasencia
Kat Plasencia

Does the fluid in the cocleah have anything do with our ability to stand? Our balance?

cooldesi30
cooldesi30

I am a medical student, and I was clueless when my medical school professor spoke about impedance matching. Your video made it easy to understand both effects. Thanks a lot Professor Samuel.

TigerTucci
TigerTucci

I love this guy!! His enthusiasm and accent makes me smile! This was a very informative and overall well made video! :)

InteractiveBiology
InteractiveBiology

Hi there! Thank you for using this video as a resource. You can include that this video was created by Prof. Leslie Samuel at the Interactive-Biology website as indicated in the above description for the video. All the best!

Sara Stevens
Sara Stevens

Hi! I want to cite this video as a source for a research paper I am writing. Could you tell me where this video was made?

koi946
koi946

this was so much useful thank u so much !!!

Natalie Hook
Natalie Hook

THIS IS GREAT. I learned about all of this in intro to audiology, but the way you worded things and paired it with the visual just made it all click. Thank you! also loved the brick/needle example. Disturbing, yet effective haha

Patti S.
Patti S.

Thank you so much! This is awesome and very interesting!

Tienyow Wong
Tienyow Wong

8:41 The hand is going to be very hurt as well :D Best video i could find in YouTube. Explained it very clearly what my physics teacher taught me in 3 lessons (I'm learning medical physics). Very helpful! Thx Again!!!

Szederp
Szederp

Forgive your writing there? Hell, if I was able to write so pretty with a mouse I would be king of the world!!! Oh and this is an excellent educational video, keep up the good work!

murrth
murrth

You can get a lot done with trial and error over the course of a couple billion years...

Cristian Cruz
Cristian Cruz

thank this video was the most informative one yet

Mrunmayee Mangale
Mrunmayee Mangale

dis video ws undoubtedly awesome...bt cud u plz design cideos fr all chapters included in biology fr standard 11th nd 12th...!!!plz...>????????????? need ur help...!!

Tebogo Brain
Tebogo Brain

i learned more from this video , i really understood mechanism behind sound wave, thanx

Rick Allen
Rick Allen

Thank you, very nicely done. As a EE, I have needed to design Impedance matching circuits many times to enable the wave power transfer from dissimilar mediums. When I first learned of this feature in the ear, the hair on the back of my neck stood up.... how could anyone, especially a scientist, not recognize the need for a complete understanding of fluid dynamics, Newtonian Physics, including the complex mathematics involved in impedance matching deny this is a designed system?