External Ear

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Del curso dictado por The University of Chicago

Understanding the Brain: The Neurobiology of Everyday Life

822 calificaciones

The University of Chicago

Understanding the Brain: The Neurobiology of Everyday Life

822 calificaciones

Learn how the nervous system produces behavior, how we use our brain every day, and how neuroscience can explain the common problems afflicting people today. We will study functional human neuroanatomy and neuronal communication, and then use this information to understand how we perceive the outside world, move our bodies voluntarily, stay alive, and play well with others.

De la lección

Hearing

The sound of birds chirping in the morning, a babbling brook or crashing waves on the beach, or warm conversation with the ones you love. The experience of all these things requires the ability to hear. Arguably the most important sense for human communication, it is also the most commonly impaired of our senses. In this module, you will learn how the human ear is artfully designed to enhance our ability to hear the human voice. You will follow sound waves as they travel from the external world, to the eardrum, through the bones of the middle ear, and to the cochlea that transduces sound information into neural impulses.

Hearing Pathways5:18

External Ear4:51

Conoce a los instructores

Peggy Mason
Professor
Neurobiology

[MUSIC]

Okay, so let's talk about the external ear.

The external ear stretches from what we call the ear which is actually called

in medical language, we call this the pinna and

then the auditory canal, the ear canal.

And it ends, the, the boundary between the external ear and

the middle ear is called the eardrum and in the vernacular, and

also called the tympanic membrane, the tympanic membrane.

So, this is all the external ear, and it all air.

So, what is the, what's the whole point of the external ear?

Well, the ear, the pinna is to gather sound.

So you can, just, just as though, if you were trying to hear somebody and

you can't quite hear them, you do this.

You're trying to get the sound to bounce off of the back of your hand, and

make it more likely that you're going to gather sound

that is coming in from all directions.

And you could put a tube here,

as Beethoven did he, when he, as he was losing his hearing he used to

use these large ear drums that would collect more sound.

No, they're not called eardrums, sorry.

The point of the earhorns, Beethoven would use a ear,

an ear horn, is to gather sound.

It's the same thing with this ear canal, you're gathering sound, but

you're doing one more thing you're, you're using something called,

instructive interference.

So, all these bouncing around sounds are going to up, and

they're going to grow in magnitude.

So that this, the amount of the intensity of the sound,

if we, if we look at the intensity of the sound from the outside to the inside,

to the point of the tympanic membrane, it's actually going to increase.

This external ear, and and as well as an ear horn.

Will serve to increase the magnitude of the sound.

Now, it, there are two additional points that I want to make about this.

First is that it doesn't increase sound at all frequentsly, frequencies equally.

The ear canal for humans is built to

increase sound in the frequencies of speech.

And it's actually built so that the, the frequencies that are not involved in

speech are reduced in magnitude, so already in the ear canal

we have a modification of what's present on the outside.

It's not a modification is not present in a simple tape recorder.

So we're already modifying the stimulus.

We're increasing frequencies related to speech, we're

decreasing the intensity of frequencies that are not related to speech.

So the second, the second point that I want to make about the external ear is.

You know, why do we increase in magnitude?

This is a teleological argument, but, the question is,

why is it advantageous to increase the amount of sound present

at the tympanic membrane, versus present at the outside of the external ear?

And the answer is because we know we are going to lose a lot

of intensity as we go through the rest of the ear.

It's inevitable, we're going to lose energy, we're going to lose sound energy.

And so this is a big boost as much as possible to increase the,

intensity of a sound prior to, to going on to the next step where we're going

to lose intensity, where it's inevitable that we're going to lose intensity.

What I've shown here is that we've, we're just considering this part,

airborne sounds are, are,

lower in magnitude at the edge of the pinna, compared to the boundary

between the external and middle ear, which is the tympanic membrane.

They grow in magnitude.

The, the bottom line is that the external ear, is going to take you

from a sound of one intensity and in, and increase the intensity of that sound,

particularly if that sound has frequencies in the speech range.

All right, in the next segment we're going to look at the middle ear.

[MUSIC]

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