Practical: Physiology of Hearing

Question 1

What is the normal range of human hearing (Hz)?

Answer 1

20-20,000Hz

Question 2

At what frequency do we here sounds best, what does this correlate with?

Answer 2

Hear sounds best at 3kHz - this is about the frequency of human voices

Question 3

High frequency sounds vibrate which part of the basilar membrane?

Answer 3

The base

Question 4

Low frequency sounds vibrate which part of the basilar membrane?

Answer 4

The apex

Question 5

Give 5 causes of sensorineural hearing deafness?

Answer 5

1) Acoustic neuroma
2) Acoustic trauma
3) Meniere’s disease (too much endolymph)
4) Presbycusis
5) Toxic degeneration of auditory nerve - drugs etc.

Question 6

What is meant by presbycusis?

Answer 6

Age related hearing loss

Question 7

Which 3 pieces of info are used to localise sound?

Answer 7

1) Interaural phase timing differences (ITD) - available from low frequencies
2) Interaural intensity/ amplitude differences - available from higher frequencies
3) Head related transfer functions (HRTF) - how the external ear modifies sound

Question 8

Which 2 pieces of information are used in horizontal localisation of sound?

Answer 8

1) Interaural phase timing differences ITD

2) Interaural intensity differences, available from high frequencies

Question 9

Why is interaural intensity differences more important for horizontal localisation of high frequency sounds?

Answer 9

Because at high frequency it is hard to detect a time difference as the waves are closer together

Question 10

What is meant by the threshold of interaural phase timing differences?

Answer 10

This is the time difference below which differences between ears cannot be detected

Question 11

How does interaural phase timing differences work?

Answer 11

Sound from the left is heard in the left ear slightly before the right

Question 12

How does interaural intensity difference work?

Answer 12

Your head creates a sound shadow. High frequency sounds have less energy than low frequency. High frequency sounds thus dissipate when they travel through solid objects (ie. your head). Your head causes energy from high frequency sounds to dissipate so the intensity in the ear furthest from the sound is reduced relative to the ear closest to the sound

Question 13

What is the umbo?

Answer 13

The most depressed part of the tympanic membrane

Question 14

When viewed with an otoscope/ auriscope, what is the small white knuckle-like process in the middle of the tympanic membrane?

Answer 14

The short process of the maleus

Question 15

When viewed with an auriscope/otoscope, what is the bright spot on the tympanic membrane due to and what does its presence confirm?

Answer 15

Due to reflection of light

Its presence may be accepted as proof of a healthy state of the membrane

Question 16

What is serous otitis media?

Answer 16

Negative pressure due to blocked eustachian tube - glue ear

Question 17

What is meant by a retraction pocket, in terms of features seen through an auriscope?

Answer 17

Tympanic membrane draped over bones

Question 18

Does horizontal localisation use monoaural or binaural clues?

Answer 18

Binaural

Question 19

Does vertical localisation use monoaural or binaural cues?

Answer 19

Monoaural

Question 20

How does vertical localisation of sound work?

Answer 20

Pressure waves are reflected off the head, shoulders and pinna. The reflections interfere subtly with the sound coming in. The pinna curvatures alters the sound differently depending on where it reflects off the pinna, ie. where it comes from - it can thus be localised

Question 21

How is air conduction and bone conduction affected in conductive deafness?

Answer 21

The patient will be deaf to air conduction but show no deafness to bone conduction

Question 22

How is air conduction and bone conduction affected in sensorineural deafness?

Answer 22

The patient will be deaf to both air and bone conduction

Question 23

How is Rinne’s test performed?

Answer 23

1) Strike the tuning fork and hold it against the subjects ear so they can no longer hear it
2) Place the tuning fork on the mastoid process and note whether or not the sound can be heard again

Question 24

What do the results of Rinne’s test tell you?

Answer 24

If the patient can hear the sound again when the tuning fork is placed on the mastoid process this suggests conductive deafness. This is because the threshold of air conduction is lower than bone conduction so in normal hearing once you can no longer hear it via air conduction you should not hear it via bone conduction. In conductive deafness the threshold of air conduction is increased so bone conduction threshold is now lower so once cannot hear it via air conduction will still be able to hear it via bone conduction.

Question 25

How is Weber’s test performed?

Answer 25

1) Strike a tuning fork and hold base firmly against pts. forehead in the midline
2) Note whether the sound is louder or quieter in each ear

Question 26

If a patient had moderate sensorineural deafness using Rinnes test, would they be able to hear the sound once the tuning fork was placed on the mastoid process?

Answer 26

No as they are deaf to both air and bone conduction

Question 27

If a patient had bilateral conductive deafness would they be able to hear the sound of the tuning fork in Weber’s test?

Answer 27

Yes - because although they are deaf to air conduction they are not deaf to bone conduction

Question 28

If a patient had moderate unilateral sensorineural deafness, what would be the result of Weber’s test?

Answer 28

Would hear the sound louder in the healthy ear

Question 29

If a patient had moderate unilateral conduction deafness, what would be the result of Weber’s test and why?

Answer 29

Sound would be heard louder in damaged ear as a result of auditory masking dampening down the sound in the healthy ear and both ears and neither ear being deaf to bone conduction

Question 30

What is meant by auditory masking, how does this change in conductive deafness?

Answer 30

Auditory masking is the dampening down on ambient sounds which don’t need to be heard - in conductive deafness eg. a perforated ear drum you lose this auditory masking ie. dampening down of sounds in that ear because you cant hear any ambient sounds

Question 31

If a patient has a normal bone conduction threshold but a reduced air conduction threshold what kind of deafness are they likely to have?

Answer 31

Conduction deafness

Question 32

If a patient has reduced bone conduction threshold and reduced air conduction threshold, what kind of deafness do they have?

Answer 32

Sensorineural deafness

Question 33

What is meant by otoacoustic emission and how is it used to detect deafness?

Answer 33

Picks up movement of hair cells when sound is made - it detects at different frequencies whether the extend of hair twitch is sufficient according to the amplification of the sound going in

Question 34

What is the one limitation of otoacoustic emission testing?

Answer 34

Provided the hair cells are functioning it cannot detect between sensorineural and conductive deafness

Question 35

When is otoacoustic emission testing particularly useful?

Answer 35

Can be used on people who cannot communicate eg. neonates, dementia, different language etc.