hearing and the ear

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. It is 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. Q: How might cupping his hands behind his ears help the boy pictured in the opening image hear better? A: His hands might help the pinna of his ears catch sound waves and direct them into the ear canal.


the sounds we hear

Sound is a form of energy that travels in waves through matter. The ability to sense sound energy and perceive sound is called hearing. The organ that we use to sense sound energy is the ear. Almost all the structures in the ear are needed for this purpose. Together, they gather sound waves, amplify the waves, and change their kinetic energy to electrical signals. The electrical signals travel to the brain, which interprets them as the sounds we hear. The Figure 1.1 shows the three main parts of the ear: the outer, middle, and inner ear. It also shows the specific structures in each part of the ear.

inner ear

The stirrup in the middle ear passes the amplified sound waves to the inner ear through the oval window. 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 many tiny hairs, as you can see in the magnified image 1.2. When the cochlea vibrates, it causes waves in the fluid inside. The waves bend the hairs on the hair cells, 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 the Figure 1.1, 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. 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. Q: Wave amplitude is the maximum distance particles of matter move when a wave passes through them. Why would amplifying the sound waves as they pass through the middle ear improve hearing? A: Amplified sound waves have more energy. This increases the intensity and loudness of the sounds, so they are easier to hear.

instructional diagrams

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functions of the ear include

-->  a) gathering sound waves.

b) amplifying sound waves.

c) changing sound waves to electrical signals.

d) all of the above

all of the following are parts of the outer ear except the

a) pinna.

b) ear canal.

-->  c) oval window.

d) eardrum.

the main role of the middle ear is to change sound waves to electrical impulses.

a. true

-->  b. false

the inner ear includes the

a) stirrup.

-->  b) cochlea.

c) anvil.

d) all of the above

you perceive a sound as soon as the sound waves strike your eardrum.

a. true

-->  b. false

diagram questions

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