February 24, 2011

039 The Function of the Organ of Corti

The organ of corti – such a small part of the cochlea with such a major function. Watch as Leslie demonstrates how the vibrations in the cochlea affect the cilia on the hair cells, and how this process is translated to hearing.

There’s also a really cool video of a hair cell dancing to Rock Music.


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 39, I’m going to be talking about the function of the Organ of Corti. And don’t worry, I won’t be singing in this episode. That’s Episode 38. So, if you want to hear me sing, go to Episode 38 and enjoy! Today, we are just going to talk about the function of the Organ of Corti. So let’s get right into it!

Now, we’ve been looking at this picture and we’ve been looking at the structure of the ear. We look at the fact that sound waves come in here; cause vibration in the tympanic membrane; causing the malleus, incus, and stapes to vibrate; and then causing the fluid inside of the cochlea to vibrate. In the last episode, we unrolled the cochlea and we looked at it like this. And we showed that, depending on where it vibrates, that’s going to send signals to the brain, and the brain can interpret that as a certain pitch, a certain frequency.

Now, there are a few things that I want you to pay attention to in this episode that we did not pay attention to in the previous episodes. And that would be here. We have the scala vestibuli. That’s this cavity at the top here. And below the basilar membrane, we have the scala tympani. And that’s the cavity at the bottom of the cochlea, beneath the basilar membrane.

And what I’m going to do in the next picture is, I’m going to actually take a cross-section. So I’m going to cut straight through the cochlea like this, and we are going to look at a cross- section of the cochlea. So let’s go to the next figure.

Here, we are looking at the cross-section of the cochlea. And here, you can see we have the scala vestibuli. And here we have the scala tympani. And here, this is the basilar membrane. And right above the basilar membrane, we have the Organ of Corti. So that’s this section right here. We can’t see too many details about it, but that is the Organ of Corti. Here we can see more details. This entire structure is the Organ of Corti.

But I just want you to pay attention to how it is laid out here, with the Organ of Corti here, scala vestibuli at the top. This is the basilar membrane. And here we have the scala tympani. One more place that I want you to pay attention to, here, is another cavity we call the cochlear duct. And once again, in here we have the Organ of Corti. So this is a cross-section of the cochlea, and that’s how it’s laid out.

Now, I want to bring your attention to the Organ of Corti which is shown clearly right here. Once again, we can see here we have the basilar membrane, and on top of that we have the Organ of Corti. A few more things to point out here. This membrane here, it says membrana tectoria. We call this the tectorial membrane.

And we look at the fact that, when sound enters the cochlea, that causes the basilar membrane to vibrate up-and-down. Now, when that vibrates up-and-down, that’s going to cause the Organ of Corti to move up and down. Then, here we have the tectorial membrane that’s attached only at one end. So, as the basilar membrane is going up-and-down and the Organ of Corti is going up-and-down, that is going to cause the tectorial membrane to move in a windshield- wiper-like fashion. So it’s just going to flap like a windshield wiper.

Now, in the Organ of Corti, we have a number of different hair cells. We have inner hair cells, which would be this one here; and we have outer hair cells, which would be these four here. Now, as you can imagine, if the entire Organ of Corti is moving up-and-down, the tectorial membrane is moving in a windshield-wiper-like fashion, that tectorial membrane is going to cause this outer part of the hair cells to vibrate. And these outer parts are called cilia. So, it’s going to cause the cilia to bend. And that’s the process that’s going to cause a signal to go via the auditory nerve to the brain.

Now, there is a very important thing to understand here. The part that responds to the tectorial membrane that is directly responsible for hearing would be the inner hair cells. And that sends a signal to the brain. However, the outer hair cells are involved in modulating the response and helping the inner hair cells so that you can hear better.

So once again, when the sound comes into the cochlea, the basilar membrane vibrates up-and-down that causes the tectorial membrane to move in a windshield-wiper-like fashion, causing the cilia and the hair cells to bend. And when the cilia and the inner hair cells bend, that causes a signal to be sent to the brain. The outer hair cells are involved in modulating the response to that sound.

Now, I have a very fascinating video to show you that’s going to show what happens to the outer hair cells in response to sound. So sit back, relax, and enjoy the ride!

{Short Video Clip of Outer Hair cell dancing to music}

So, as you can see in a very interesting way, this hair cell was vibrating up-and-down. It was vibrating in response to the sound. And that process is involved in modulating the response to hearing. This causes signals to be sent to the brain and the brain gets a full picture of the sound that you are listening to.

That’s it for this video. If you have any questions, as usual, leave them in the comments section below. And you can always visit the website at Interactive-Biology.com for more Biology videos and other resources. That’s it for now, and I’ll see you in the next one.

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