hearing loss

Question 1

Why is it hard to diagnose issues with auditory system

Answer 1

Cochlear in cavity of temporal bone
Delicate structure surrounded by thick bone

Question 2

Conductive hearing loss

Answer 2

Ear canal blocked
Ear drum perforated
Ossicles dislocated
Ossicles immobilised
Middle ear filled with fluid

Question 3

Sensorineural hearing loss

Answer 3

Loss of perilymph
Loss/absence of outer hair cells
Loss/absence of inner hair cells
Loss of endocochlear potential
Loss of auditory nerve fibres
Meniere’s disease
Tinnitus

Question 4

Pure tone audiology

Answer 4

Used to look for absolute threshold of sound

Question 5

Air-bone gap

Answer 5

Normal with bone vibrator but not with headphones = conductive hearing loss
Different in both headphones and bone vibrator = sensorineural hearing loss

Question 6

Bone vibrator

Answer 6

Testing bone conducted thresholds
Bypass middle ear problems

Question 7

Loss of outer hair cells

Answer 7

Most prevalent issue in elderly people

Question 8

De-activation of outer hair cells with furosemide - Ruggero (1991)

Answer 8

Responses drop dramatically after 14 mins
After time it goes back to normal
Pattern of the de-activation follows loudness perception
Hair frequencies only amplify at certain frequencies as furosemide won’t affect perception of sound at 1000Hz

Question 9

Loudness magnitude estimation

Answer 9

Hearing impaired listeners lack normal compressive growth in loudness
If hearing impairment very bad then loudness just goes rapidly up because hair cells weren’t doing anything anyway
Why old people say speak up then no need to shout

Question 10

Frequency selectivity

Answer 10

If you are good at detecting frequencies then you can detect a frequency in a narrow gap between tones
If you are not good at detecting frequencies then you have to adjust the boundaries of the tone

Question 11

Glaseburg (1986)

Answer 11

Patients deaf in just one ear
In impaired ear thresholds fall slowly and widening of the difference between frequencies doesn’t help
Passive filtering of cochlear is worse at detecting frequencies than outer hair cells

Question 12

Inner hair cells

Answer 12

Transmute sound into electrical signals and send it off to brain
More likely to keep them compared to outer hair cells

Question 13

Dead regions

Answer 13

Relevant for audiology
Hard to identify dead regions because hairs will still vibrate even if they are displaced from peak frequency

Question 14

Moore (2000)

Answer 14

To prevent misidentification of dead zones, you add noise
Thresholds in noise are going to be less affected
Called threshold equalising noise (TEN)

Question 15

Loss of cochlear potential

Answer 15

No voltage then inner or outer hair cells won’t work properly and have smaller voltage change
In animal models, endocochlear potential falls in age

Question 16

What does loss of endocochlear potential look like

Answer 16

Affects full cochlear, uniform across frequency
Don’t know how much OHCs amplify at low frequency because of difficulty in examining cochlear

Question 17

Cochlear Synaptopathy (Hidden hearing loss) - Liberman (2009)

Answer 17

Looked at mice and how their auditory nerve fibres were affected after experiencing ONE loud noise
Post mortem, mice had lost huge numbers of auditory nerve fibres compared to non-exposed mice
Absolute threshold was elevated

Question 18

Cochlear synaptopathy evidence in humans

Answer 18

Number of inner hair cell synapses in cadaver temporal bones declines with age at death