February 18, 2011

036 An Overview of the Mechanism of Hearing

 In this episode, Leslie talks about how we hear sounds. From the external ear to the eardrum, down to the 3 bony ossicles, then to the cochlea to be sent as signals towards the brain, it is all explained in this video.


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. In this episode, Episode 36, I’m going to be giving an overview of the mechanism of hearing. Now, you’re listening to this video right now, well you’re watching this video right now, and you’re hearing the words that I’m saying that have been recorded. What we’re going to do is look at how that process happens. So let’s get right into it.

We’re looking at a drawing of the ear, and there are a few things that I want to point out here. Here we can see that this is the external part, so this is the external ear. Then we have this section here, and that is called, I’m going to draw a line down here, that’s called the external auditory canal. Then here, there’s a structure that we call the eardrum. Connected to the eardrum, we have 3 small bones. We call them the 3 bony ossicles: the malleus, the incus, and the stapes. Depending on which book you read, you’ll see malleus, incus, and stapes, or hammer, anvil, and stirrup. They all mean the same thing. This is the hammer, this is the anvil, and this is the stirrup. I’m going to be using malleus, incus, and stapes. The way I typically remember this is MIS, mis: malleus, incus, and stapes. Those are the 3 bones. One here, one there, and this is the third one here.

Then we have this structure here that looks kind of like a snail, and that is called the cochlea. Then we have, let me do this in a different color, we have this structure here, and that is the auditory, of course, because it deals with hearing, the auditory nerve. That, of course, goes to the brain. So these are the parts that I want you to pay attention to. Once again, we have the external ear, and in some places, you’re going to see this called the pinna. Then we have the external auditory canal, we have the eardrum, malleus, incus, and stapes, the cochlea, and the auditory nerve.

There are a few other things that we have, like these are called the semicircular canals. I’m not going to talk about that much today. And then we have this connection here where the stapes connects to the cochlea, and that’s called the oval window. And then there’s the round window on the other end of the cochlea. So these are the parts that I want you to know. Now we’re going to talk about how hearing happens. We’re going to give an overview of the mechanism of hearing.

Now, sound exists as waves. You have particles in the ear that are vibrating back and forth, and there’s kind of like an oscillation. That is how the sound starts. Something vibrates, causing the ear to vibrate, and what you’re hearing is a result of this process. So the sound waves are coming from some source, let’s say you’re listening to this right now, which you are. We have sound waves that are coming from the speakers. The speakers are vibrating back and forth. The external ear focuses those sound waves into the external auditory canal. The air molecules are vibrating back and forth, and that vibration comes and strikes the eardrum. When the sound waves strike the eardrum, the eardrum is going to vibrate back and forth. The malleus, incus, and stapes are connected to the eardrum. The malleus is connected to the eardrum directly, the incus is connected to the malleus, and the stapes is connected to the incus. So that causes those bones to vibrate.

When those bones vibrate, it’s going to cause the oval window to vibrate. In the cochlea, which is what it’s connected to, we have fluid inside that cochlea. When the oval window vibrates, the fluid inside the cochlea is going to vibrate, and that’s going to cause a series of vibrations. We’re going to look at what’s going on in here in more detail in the next episode, but the vibration in here is going to cause a signal in the auditory nerve, and that signal then travels to the brain.

So we have the same general mechanism when it comes to senses. There are receptors inside of this cochlea that’s going to respond to the vibrating fluids. That’s going to cause a receptor potential that is going to cause a signal to be sent to the brain, and then the brain is going to interpret that signal. In this case, it’s going to interpret it as sound, and you’re going to hear what I’m saying or you’re going to hear something that you’re listening to. Whatever is the source of that sound, you will be able to hear it because the brain is interpreting what is happening with the receptors that are found inside the cochlea.

There’s one more term I’d like to point out, and that is the eardrum. Another name for the eardrum is also the tympanic membrane. So if you ever hear me referring to tympanic membrane, that is exactly the same thing as the eardrum.

I have an animation to show you that depicts this entire process, and you can see that here. There are a few things I want to point out. You can see the sound waves coming in here, and then you can see the vibrating eardrum. Then you can see the bones, the 3 bony ossicles: malleus, incus, and stapes. Those are vibrating, causing stuff to happen in the cochlea. Of course, I’m being a little vague there, but we’re going to get into more detail in the next episode. In response to these sensory receptors detecting that vibration, that’s going to cause a signal in the auditory nerve that goes to the brain.

So there you have it. You can see the entire process happening. This, of course, is just an animation, but it gives you a good overview of how hearing takes place. If you have any questions, of course you can leave them in the comments section below, and I’ll be happy to answer your questions. You can always visit us at www.Interactive-Biology.com for more biology videos and other resources to help make biology fun. That’s it for this video, and I’ll see you in the next one.

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