A/V equipment needed: LCD projector for powerpoint slides OR overhead projector for transparencies

Supplies (optional): Ear model, decibel meter, tuning fork, ping pong ball taped to string (app. 6"), blow dryer, blender, pair of ear plugs for each student.

Time needed: One class period; app. 45 min.

Outline

Introduction
        The tragedy of hearing loss
        Prevalence of noise-induced hearing loss

Sound
        How sound waves are generated
        Properties of sound: pitch and loudness

Structure of the human ear
        Outer ear and function
        Middle ear and functions
        Inner ear and functions

How loud noise damages the inner ear
        Hair cells
        Damage is permanent

Examples of damaging noises
        Household
        Other sources of loud noise
        The most damaging noises
        Loud noises measured in San Antonio

Protecting ears from excessive noise
        Turn it down
        Walk away
        Use ear plugs

Sample lecture: This is not intended to be memorized but to give instructor an idea of how the talk might be organized. Text in brackets indicates interaction with students.

Picture yourself in the cafeteria eating your lunch, surrounded by your friends.

They're all talking and laughing, and you can only understand about every other word. You don't want to keep asking them to repeat themselves, because you've learned that that will annoy them after awhile. So you don't really know what they're talking about or whether they're talking and laughing about you.

[How does it feel?]

Yes, I imagine pretty disconnected, frustrated, depressed, maybe even a little paranoid. Well, this is what it is like to have mild hearing loss, and this can happen to you from repeated exposed to loud noise.

(Alternative intro:
[How many of you know that you're not supposed to stare at the sun? Of course, you all know that. Why is it bad?] How surprising it is that so few people know that it can damage your ears to listen to loud noise.)

Five million kids from 5 to 19 years old already have some degree of hearing loss, and many more will develop it as they get older. Some hearing loss is due to normal aging, but many, many persons develop serious hearing loss by the time they're 50 or so or because noise has damaged their ears.

Pretty sad, huh? But the good news is that such hearing loss, called noise-induced haring loss, is preventable. But you have to be willing to be nice to your ears.

SLIDE/OVERHEAD: Who is affected by noise-induced hearing loss?

SLIDE/OVERHEAD: What is sound?

In a minute we'll look at the structure of the ear and how it can be damaged by loud noise, but first let's explore some of the properties of sound. Sound is a perception, a creation of your brain, in response to pressure waves in the environment. These pressure waves are like vibrations of air (or water) occurring when air molecules bump into each other and then bounce off and then bounce into other molecules and so on and so on. These pressure waves can be generated in different ways, for example by striking an object or by air being forced through your vocal cords.

[Do any of you play musical instruments? Who plays a wind or brass? String instruments? Percussion?]

They all work by causing air to vibrate in one way or another. By the way, different types of instruments sound different because even if they play the same note, the vibrations of not all exactly the same frequency, but a mixture, and our brain interprets these mixtures as different qualities of sound. Same with voices.

[Activity: Let students hear tuning fork. Also, bang tuning fork and immediately put in glass of water to see agitation as proof that tuning ford is vibrating. OR Let vibrating tuning fork touch ping pong ball hanging by string.]]

If the air molecules are being caused to vibrate very fast your brain will interpret the sound higher-pitched than if the vibrations are slower. The number of vibrations per second is called the frequency. Middle C, for example, has a frequency of 256 whereas an octave lower is half of that, or 128. The other important property of sound, and the one we're really interested in today is loudness. This is determined by how big the pressure waves are, or how hard the air molecules are bumping into each other. Loudness is also called amplitude. The bigger the wave, the louder it sounds to us.

Loudness, or amplitude, is measured in units called decibels. Normal speech is about 65 decibels. For every increase in 10 decibels it means the sound is 10X louder. Sounds of 85 decibels or higher can damage your ears because the vibrations are so energetic that they can destroy delicate cells deep in your ear. Let's take a quick look at the structure of the ear and how loud noise can damage it.

SLIDE/OVERHEAD: The Human Ear

There are three main parts to the ear. Here's the outer part. It acts like a funnel for the pressure waves to enter. There are glands in the ear canal that manufacture wax--it's really called cerumen--to catch dirt and insects. Sometimes it collects in there and can impede hearing a bit.

If you think you have a lot of wax in your ears you can ask the school nurse or your doctor to look in your ears and see. The wax can be washed out easily.

This is the eardrum, or tympanic membrane. It's a real drum: when the pressure waves come to it, it vibrates at the same frequency as the waves.

On the other side of the eardrum is a compartment called the middle ear. This is where, by the way, common ear infections--maybe many of you had these when you were younger--occur, because if is connected to the throat by this tube (so a sore throat can lead to a middle ear infection).

In the middle ear are the three teeny bones you probably all know by name: the malleus, the incus, and the stapes. The first one is connected to the eardrum, and the three bones are connected to each other, so when the eardrum vibrates, the little bones do too. Their purpose actually is to amplify the pressure waves. This makes your ear more sensitive to sounds than it would be without the little bones.

The third part of the ear is the inner ear, and it is, in my opinion, one of the most amazing, complex, and beautiful parts of the body. The inner ear is filled with fluid, some very special sensory cells called hair cells, and nerve cells. When the third little bone in the middle ear vibrates, it stomps on the entrance to the inner ear and sets up vibrations there. The hair cells jiggle--the cilia actually bend--and this tells the nerve cells to signal the brain. So the brain interprests the jiggling hair cells as sound. And as you remember, the faster the jiggling, the higher the pitch, or note of the sound, and the stronger the jiggling, the louder the sound.

[Activity: show structures on model]

SLIDE/OVERHEAD: Scanning electron micrograph of hair cells (available on transparency only)

Here we're using an electron microscope to look at the surface of some human hair cells in the inner ear. See how organized they are? They're situated in rows. These white hair-like structures are the cilia poking out from the tops of the cells.

SLIDE/OVERHEAD: Noise and its effect on hearing

Really loud sounds destroy the cilia because really strong pressure waves cause really rough jiggling, and sometimes it's just too much for the delicate cells, especially the cilia. The cilia get broken off the hair cells, and the hair cells die. Thus, the brain doesn't get the signal and hearing is impaired. Hair cells do not grow back. When this type of damage occurs it's called sensory hearing loss. Some hair cells die with normal aging and sometimes a hearing aid will help,. But damage due to loud noise is preventable!

SLIDE/OVERHEAD: How long can you listen?

SLIDE/OVERHEAD: Examples of dangerous sound levels

If you're exposed to really loud noise for a short time, say a band concert, sometimes for awhile your hearing may be muffled or you might hear ringing in your ears. Usually, this is temporary, and your ears will go back to normal. However, the more you're exposed to loud noise, the higher the chances that permanent damage will occur. In other words, the damage adds up over years. Also, there are some types of noises, like firecrackers or gunshots that go off near you that can cause permanent damage the very first time. Remember, once damage occurs, your ear cells never get better.

[Activity: Measure sounds such as blender, hair dryer, voices with decibel meter.]

SLIDE/OVERHEAD: Loud noise measured around San Antonio locations

SLIDE/OVERHEAD: More examples of things that cause too much noise

So how do you know if a certain loud noise is damaging your ears? Well, you don't need a decibel meter to find out. The main thing to remember is that is a loud noise is making your ears hurt or even uncomfortable, then it's probably doing some harm, and you need to do something about it.

SLIDE/OVERHEAD: How can you protect your inner ears?

Either turn it down, walk away, or wear ear plugs. Everyone should get in the habit of carrying around a pair of ear plugs in their purse, pocket, or backpack and to use them when needed. Keep some at home too.

[Activity: Give each student a pair of earplugs and show how to use and give instructions how to wash, or, if disposable, advise to buy more. Could compare sound of loud blender, for example, with and without ear plugs.]

Always remember to be kind to your inner ears!!!

Helpful resources:

Any human anatomy/physiology text
Any encyclopedia: "Sound"
Organizations:
        National Hearing Conservation Association: www.hearingconservation.org
        Dangerous Decibels: www.dangerousdecibels.org
Physician Assistant Studies Dept., Univ. of Texas Health Science Center at San Antonio

SLIDES/OVERHEADS:

(Powerpoint and overheads)

1. What is sound? - Short text
2. Properties of sound
3. How is loudness measured?
4. Anatomy of the ear
5. How do we hear? - Summary
6. Hair cells
7. How does loud noise damage the inner ear?
8. Sounds above 85 decibels can damage your ears.
9. Loud household noises
10. Really dangerous noises
11. Loud noises around San Antonio
12. How can you protect your inner ears?
13. Remember: Be kind to your inner ears!!

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For information contact lawson@uthscsa.edu or pinkson@uthscsa.edu
Copyright 2003 UTHSCSA - Revised 5/27/2003