The ear and hearing

Question 1

Most of sound conduction and processing takes place where?

Answer 1

In the petrous part of the temporal bone

Question 2

What are the name of the glands which secrete earwax?

Answer 2

Ceruminous glands

Question 3

What is the role of earwax?

Answer 3

Sticks to dust and other particles to stop them getting too far into the body

Question 4

What is the role of the ossicles?

Answer 4

Provide amplification and gain to sound, they are like a lever system.
Lever systems act to increase the energy within a system

Question 5

How do ossicles increase energy?

Answer 5

1. The footplate of the stapes has a SA 17x smaller than that of the eardrum, so you are taking the vibrations of the ear drum and concentrating them into a much smaller SA, increasing/amplifying the sound by 17x
2. The lever arm factor of the whole system is about 1.3, so we can multiply the 17x area difference by 1.3 and we end up with a pressure gain of 20 or more.
   - So we are improving our hearing by 20x just with these 3 small bones

Question 6

The facial nerve runs in the facial canal and gives off two branches which enter the middle ear cavity, what are they?

Answer 6

1. The chorda tympani
   - runs between the incus and malleus
   - serves the taste buds on the anterior 2/3 of the tongue
2. The stapedial nerve
   - innervates the stapedius muscle

Question 7

The tensor tympani is innervated by which nerve?

Answer 7

The mandibular part of the trigeminal nerve

Question 8

Bone conduction can be the basis of hearing aids for people with reduced function of which part of the ear? Explain how?

Answer 8

• External or middle ear
• The external & middle ear can be bypassed by using a hearing aid that screws into the skull just above the ear and transmits the sound through the bones of the skull, particularly the petrous bone, going straight into the inner ear from here, bypassing the middle ear

Question 9

Why does one’s voice sound different on voice recordings?

Answer 9

Because voice recordings pick up air conduction not bone conduction, that is why we sound different as we are missing the lower frequencies that we normally hear when we speak

Question 10

Conductive and sensorineural hearing loss can be distinguished by which tests?

Answer 10

Rinne and Webbe tests

Question 11

What is the function of the Rinne test?

Answer 11

To measure relative conduction of sound through air and bone

Question 12

In a normal ear, which is greater, air conduction of bone conduction?

Answer 12

Air conduction > Bone conduction

Question 13

What is the problem with the Rinne test?

Answer 13

Although it will correctly identify conductive hearing loss (when BC>AC, so the tuning fork will no longer be heard when moved over the ear), if the patient is suffering from sensorineural hearing loss (AC>BC), it will produce the same result as a healthy patient

Question 14

Following the Rinne test, which test is performed to establish between conductive and sensorineural hearing loss?

Answer 14

Weber’s test

Question 15

Weber’s test works best when?

Answer 15

When the patient knows they have a problem and it is a UNILATERAL problem

Question 16

How does the Weber’s test distinguish between conductive and sensorineural hearing loss?

Answer 16

When the 256Hz tuning fork is held against the middle of the forehead, the patient is asked to report in which ear the sound is the loudest

• If the normal ear hears the sound louder, then hearing loss is sensorineural in the other ear. This is because, in the normal ear, sound travelling directly to the inner ear via skull bones is masked by ambient noise entering the middle ear
• If the defective ear hears the sound louder, hearing loss is conductive. This is because there is reduced sound travelling through the middle ear, so sound travelling from the tuning fork to inner ear via the skull is louder