Inner Ear - Hearing

Question 1

What is included in the hearing mechanism?

Answer 1

Outer ear, middle ear, inner ear, and central connections

Question 2

What is included in the inner ear?

Answer 2

Semi circular canals
Cochlea

Question 3

What is the function of the middle ear?

Answer 3

Transforms acoustic energy from medium of air to medium of fluid
Acts as sound amplifier

Question 4

How does the middle ear act as a sound amplifier?

Answer 4

Area effect of the tympanic membrane - ratio of TM to staples footplate is 7:1
Lever action of ossicular chain - ration of pressure on staples footplate to on malleus is 1.3:1

Question 5

Describe otitis media with effusion

Answer 5

Glue ear
Affects the movement of the tympanic membrane
Causes conductive hearing loss

Question 6

Describe a small perforation and hearing loss

Answer 6

Effect on hearing is variable so may not impact greatly
Main indication for repair is recurrent infections

Question 7

Describe subtotal perforation and hearing loss

Answer 7

If sensorineural function is maintained then max. hearing loss is 60dB

Question 8

Describe otosclerosis and hearing loss

Answer 8

Depression of new bone where footplate of staples fits into oval window - lever action lost
Conductive hearing loss

Question 9

Describe the structure of the cochlea

Answer 9

Pressure wave flows up scala vestibuli from piston action of staples - through helictotrema at apex and down scala tympani
Pressure differential deflects the basilar membrane of scala media

Question 10

Explain the hearing mechanism in the cochlea

Answer 10

Footplate moves in and out of oval window creating a traveling wave in the scala vestibuli and scala tympani of the cochlea
Causes movement of basilar membrane and movement of inner and outer hair cells in organ of corti

Question 11

Explain the movement of cilia in the hearing mechanism of cochlea

Answer 11

Cilia of hair cells are deflected by movement and ion channels open
Cations flow from endolymph into hair cells
Depolarisation takes place

Question 12

Explain depolarisation in hearing mechanism of cochlea

Answer 12

Impulse is then sent up to cochlea nerve
Inner hair cells activate afferent nerves
Outer hair cells modify the response of inner hair cells

Question 13

Describe the tonotopic arrangement

Answer 13

For every frequency there is specific place on basilar membrane where hair cells are maximally sensitive to that frequency
More sensitive closer to middle ear

Question 14

Where is the tonotopic arrangement?

Answer 14

Continues through auditory pathway up to acoustic area of temporal lobe (ear to brain)

Question 15

How is hearing assessed?

Answer 15

Clinical testing
Tuning fork tests
Audiometry
Objective testing

Question 16

What are the 2 tuning fork tests?

Answer 16

Weber
Rinne
Help differentiate between conductive (blocking/stopping) loss or sensorineural loss (cochlea or nerve)

Question 17

What is the Weber test?

Answer 17

Test for lateralisation
Tests both ears
Conductive - louder in ear with problem

Question 18

What is the Rinne test?

Answer 18

Test which compares loudness of perceived air conduction to bone conduction in one ear at a time
Conductive - louder at bone

Question 19

What are the different types of audiometry?

Answer 19

Pure tone
Visual reinforcement
Play
Tympanometry

Question 20

What physical properties are useful in assessment of hearing ability?

Answer 20

Frequency and volume

Question 21

Describe pure tone audiometry

Answer 21

Determines the faintest tones a person can hear at selected pitches from high to low
Headphones are worn
Looking for threshold

Question 22

What is presbycusis?

Answer 22

High tone hearing loss which is age related

Question 23

What is the air-bone gap?

Answer 23

Bone conduction perception is greater than air conduction perception - conductive loss

Question 24

What is is used for objective testing?

Answer 24

Otoacoustic emissions - OAEs

Question 25

Describe otoacoustic emissions

Answer 25

Sounds given off by inner ear when cochlea is stimulated by sound.
When sound stimulates cochlea - outer hair cells vibrate
This causes nearly inaudible sound which echoes to middle ear and can be measured with small probe

Question 26

When is the OEA test used?

Answer 26

Often part of new born hearing screening test
Normal - produce emissions
If hearing loss grater than 25-30dB then don’t produce emissions

Question 27

Describe tympanometry

Answer 27

It assists in detection of fluid in middle ear, perforation of eardrum, and wax blocking the ear canal

Question 28

How does tympanometry work?

Answer 28

Pushes air pressure into ear canal making eardrum move back and forth
Test measures pressure in middle ear and mobility of eardrum
Can show stiff eardrum, hole in eardrum, or eardrum moves too much

Question 29

What is the management for hearing loss?

Answer 29

Surgery
Sound amplification
Direct stimulus of cochlear nerve cells

Question 30

Describe bone anchored hearing aid?

Answer 30

Osseous integrated screw into skull
Microphone and amplifier clip onto abutment or attach by magnet
Sound conducts from skull to cochlea
Requires 50dB sensorineural threshold

Question 31

When is bone anchored hearing aid (BAHA) used?

Answer 31

When anatomy makes conventional aid difficult
Persistent otitis externa
External canal atresia

Question 32

Describe a cochlear implant

Answer 32

Very strong hearing aid
Electrode placed inside cochlea
For those with profuse hearing loss