hearing sound

who needs hearing protection

People who work in jobs that expose them to loud sounds must wear hearing protectors. Examples include construc- tion workers who work around loud machinery for many hours each day (see Figure 20.10). But anyone exposed to loud sounds for longer than the permissible exposure time should wear hearing protectors. Many home and yard chores and even recreational activities are loud enough to cause hearing loss if people are exposed to them for very long.

how we hear

Figure 20.7 shows the three main parts of the ear: the outer, middle, and inner ear. It also shows the specific structures in each part. The roles of these structures in hearing are described below and in the animations at these URLS: (1:43) MEDIA Click image to the left or use the URL below. URL:

outer ear

The outer ear includes the pinna, ear canal, and eardrum. The pinna is the only part of the ear that extends outward from the head. Its position and shape make it good at catching sound waves and funneling them into the ear canal. The ear canal is a tube that carries sound waves into the ear. The sound waves travel through the air inside the ear canal to the eardrum. The eardrum is like the head of a drum. Its a thin membrane stretched tight across the end of the ear canal. The eardrum vibrates when sound waves strike it, and it sends the vibrations on to the middle ear.

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preventing hearing loss

Hearing loss caused by loud sounds is permanent. However, this type of hearing loss can be prevented by protecting the ears from loud sounds.

hearing loss

All these structures of the ear must work well for normal hearing. Damage to any of them, through illness or injury, may cause hearing loss. Total hearing loss is called deafness. To learn more about hearing loss, watch the animation at this URL: (1:39). MEDIA Click image to the left or use the URL below. URL: Most adults experience at least some hearing loss as they get older. The most common cause is exposure to loud sounds, which damage hair cells. The louder a sound is, the less exposure is needed for damage to occur. Even a single brief exposure to a sound louder than 115 decibels can cause hearing loss. Figure 20.9 shows the relationship between loudness, exposure time, and hearing loss.

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inner ear

The stirrup passes the amplified sound waves to the inner ear through the oval window (see Figure 20.7). When the oval window vibrates, it causes the cochlea to vibrate as well. The cochlea is a shell-like structure that is full of fluid and lined with nerve cells called hair cells. Each hair cell has tiny hair-like projections, as you can see in Figure and this triggers electrical impulses. The electrical impulses travel to the brain through nerves. Only after the nerve impulses reach the brain do we hear the sound.

middle ear

The middle ear contains three tiny bones (ossicles) called the hammer, anvil, and stirrup. If you look at these bones in Figure 20.7, you might notice that they resemble the objects for which they are named. The three bones transmit vibrations from the eardrum to the inner ear. They also amplify the vibrations. The arrangement of the three bones allows them to work together as a lever that increases the amplitude of the waves as they pass to the inner ear.

how hearing protectors work

You can see two different types of hearing protectors in Figure 20.11. Earplugs are simple hearing protectors that just muffle sounds by partially blocking all sound waves from entering the ears. This type of hearing protector is suitable for lower noise levels, such as the noise of a lawnmower or snowmobile engine. Electronic ear protectors work differently. They identify high-amplitude sound waves and send sound waves through them in the opposite direction. This causes destructive interference with the waves, which reduces their amplitude to zero or nearly zero. This changes even the loudest sounds to just a soft hiss. Sounds that people need to hear, such as the voices of co-workers, are not interfered with in this way and may be amplified instead so they can be heard more clearly. This type of hearing protector is recommended for higher noise levels and situations where its important to be able to hear lower-decibel sounds.

instructional diagrams

No diagram descriptions associated with this lesson

questions

Bones in the ear canal transmit sound waves to the middle ear.

a. true

-->  b. false

Which choice shows the correct sequence in which sound waves travel through the ear?

-->  a. ear canal  eardrum  hammer

b. anvil  oval window  ear canal

c. stirrup  pinna  eardrum

d. eardrum  ear canal  cochlea

The stirrup passes amplified sound waves to the oval window.

-->  a. true

b. false

In which structure of the ear are sound waves changed to nerve impulses?

a. eardrum

b. stirrup

c. oval window

-->  d. cochlea

We hear sound as soon as sound waves reach the middle ear.

a. true

-->  b. false

Which structures are found in the outer ear?

a. anvil, pinna, eardrum

-->  b. pinna, ear canal, eardrum

c. ear canal, cochlea, stirrup

d. hammer, pinna, ear canal

Functions of the ossicles include

a. amplifying sound waves.

b. transferring sound waves.

c. catching sound waves.

-->  d. two of the above

Most adults experience at least some hearing loss as they get older.

-->  a. true

b. false

The most common cause of hearing loss is exposure to loud sounds.

-->  a. true

b. false

Which decibel level of sound has the longest permissible exposure time?

-->  a. 85 dB

b. 100 dB

c. 106 dB

d. 115 dB

Long-term exposure to loud sounds is needed to damage hearing.

a. true

-->  b. false

Many home and yard chores are loud enough to cause hearing loss.

-->  a. true

b. false

Electronic hearing protectors reduce the amplitude of high-amplitude sound waves.

-->  a. true

b. false

The brain interprets nerve impulses from the ears as sounds.

-->  a. true

b. false

Materials used for earplugs include silicon and polyurethane foam.

-->  a. true

b. false

The brain plays an essential role in hearing.

-->  a. true

b. false

part of the ear that extends outward from the head

a. middle ear

b. ear canal

c. cochlea

-->  d. pinna

e. eardrum

f. hair cell

g. ossicle

The most common cause of hearing loss is damage to the eardrum.

a. true

-->  b. false

any of three tiny bones in the middle ear

a. middle ear

b. ear canal

c. cochlea

d. pinna

e. eardrum

f. hair cell

-->  g. ossicle

fluid-filled structure in the inner ear that is lined with hair cells

a. middle ear

b. ear canal

-->  c. cochlea

d. pinna

e. eardrum

f. hair cell

g. ossicle

The role of hearing protectors is to keep foreign objects out of the ears.

a. true

-->  b. false

tube that carries sound waves into the ear

a. middle ear

-->  b. ear canal

c. cochlea

d. pinna

e. eardrum

f. hair cell

g. ossicle

The eardrum is the first structure of the ear to vibrate when sound waves strike it.

-->  a. true

b. false

Waves in cochlear fluid bend the hair-like projections of hair cells.

-->  a. true

b. false

membrane in the outer ear that vibrates when sound waves strike it

a. middle ear

b. ear canal

c. cochlea

d. pinna

-->  e. eardrum

f. hair cell

g. ossicle

tiny structure in the inner ear that changes vibrations to nerve impulses

a. middle ear

b. ear canal

c. cochlea

d. pinna

e. eardrum

-->  f. hair cell

g. ossicle

part of the ear that transmits and amplifies vibrations from the eardrum

-->  a. middle ear

b. ear canal

c. cochlea

d. pinna

e. eardrum

f. hair cell

g. ossicle

The arrangement of the ossicles in the middle ear allows them to work together as a(n)

a. inclined plane.

b. wedge.

c. screw.

-->  d. lever.

When the oval window in the ear vibrates, it causes vibrations in the

a. anvil.

-->  b. cochlea.

c. hammer.

d. eardrum.

Which of the following ear structures is damaged by excessive exposure to loud sounds?

a. pinna

b. ossicle

-->  c. hair cell

d. ear canal

When the cochlea vibrates, it causes

-->  a. waves to pass through the cochlear fluid.

b. sound waves to increase in frequency.

c. the ossicles to start vibrating faster.

d. two of the above

Hearing loss due to exposure to loud sounds is

a. common.

b. permanent.

c. preventable.

-->  d. all of the above

Activities that may expose people to dangerously loud sounds include

a. lawn mowing.

b. snowmobile riding.

c. construction work.

-->  d. all of the above

Which statement about electronic hearing protectors is true?

a. They muffle all sounds.

-->  b. They generate anti-noise sound waves.

c. They send electronic signals to the brain.

d. They use insulation to block sound waves.

diagram questions

No diagram questions associated with this lesson