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NHB > Hearing > Flashcards

Hearing Flashcards

1
Q

What are “sound”?

Is this the only thing that can elicit an auditory sensations

A

Small fluctuations in air pressure

No - any vibration transmitted to the ear can

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2
Q

What can complex vibrations be resolved into

A

The sum of individual sinusoidal vibrations

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3
Q

Describe a sine wave

A

An individual sinusoidal vibration

Characterised by 3 parameters: frequency, amplitude and phase

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4
Q

Subjectively what do changes in amplitude and frequency of sine waves correspond to

A

Amplitude- loudness

Frequent- pitch

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5
Q

How sensitive are we to changes of phase in sine waves

A

We are relatively insensitive to changes in the phase of a sound and thus there is no subjective correlate for phase

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6
Q

What is the range of intensities that we can hear

A

> 10^12:1

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7
Q

What is the unit of power used in auditory research

A

1/10 of a Bel (decibel)

Decibels are RATIOS!!!

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8
Q

What is the reference value in human psychoacoustics

What is the importance of this

A

20μPa

The strength of the signal is indicated relative to this value

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9
Q

What is 1Pa in N/m^2

A

1:1

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10
Q

What is the frequency threshold for human hearing

A

3kHz

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11
Q

What is dB SPL

A

Decibels sound pressure level

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12
Q

What does 0 dB mean

A

The sound has the same pressure as reference (log1=0)

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13
Q

How do you express a level of zero sound in dB

A

You can’t!!! Log0=-infinity

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14
Q

Negative values of dB mean negative sound. True or false?

A

False

The specified sound is simply less than reference

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15
Q

What does dB SPL=?

A

20log(Pressure/20μPa)

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16
Q

What is the speed of sound

A

340m/s in air

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17
Q

f=?

A

1/p

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18
Q

What does λ=

A

(1/f)x c

where c = speed of sound (~ 340 metres/s in air)

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19
Q

What is a band stop filter

A

Only passes frequencies outside a restricted bandwidth

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20
Q

How can the auditory pathway be divided

A

Into peripheral (ear and auditory nerve) and central (nuclei and pathways from cochlear nucleus to auditory cortex)

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21
Q

How is the ear divided

A

Outer - pinna and external auditory meatus
Middle - tympanic membrane, ossicles and middle ear cavity
Inner- cochlear (and vestibular apparatus)

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22
Q

How does the ear canal act

A

As an open ended tube with resonant peaks that are predictable from knowing its height (2-3cm in man)

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23
Q

Generally why is the pinna useful

A

Can assist in sound localisation by modifying spectra of sounds in a space dependant manner

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24
Q

Where is the azimuthal location of 90 degrees

A

Directly in line with left pinna

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25
Q

What is HRTF

Where do direction dependant notches and peaks appear

A

Head related transfer function

The pressure transformation from free field to the tympanic membrane

Above 5kHz

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26
Q

What does the first spectral notch of the HRTF provide

A

A cue for sound localisation, particularly elevation (vertical plane)

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27
Q

What happens when we fit a mold to the external ear

What happens if it is left in for several weeks
Why

What happens after its removal
What does this suggest

A

Disrupts the ability to make judgements about elevation

Errors in localisation disappear after time - they had learnt to associate new spectral cues with direction in space

Could localise just as well immediately after
Multiple representations of auditory space can co-exist

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28
Q

Given that it took several weeks for a new representation to be formed after insertion of a mould into the external ear how would this presentation be formed

What is this similar to

A

By neural growth of novel connections

Being bilingual - first and second languages are processed un different regions of the cortex

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29
Q

What are the functions of the middle ear (3)

A

Impedance matching between air and cochlear folds

Protection from loud sounds (including own vocalisations)

Anti masking or high frequency sounds by low frequency sounds (particularly at high sound levels)

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30
Q

What is the purpose of the middle ear muscles

A

To dampen the vibrations of the ossicles thereby reducing the acoustic signal that reaches the ears

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31
Q

When do the middle ear muscles contract

A

100ms AFTER exposure to a loud sound and BEFORE a person vocalises

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32
Q

Do frogs have middle ear muscles

A

No as they do not vocalise

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33
Q

True or false

Middle ear muscles attenuate high frequencies more than low

A

Faults they attenuate low frequencies more than high

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34
Q

Where do the tensor tympani and stapedius attach

A

TT- neck of malleus

Stapedius- neck of stapes

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35
Q

Which muscles in humans are active when exposed to loud sounds

A

Only stapedius

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36
Q

What is the threshold for the middle ear muscle reflex to be activated

Is this bilateral or unilateral

A

Sounds 80 dB above a persons hearing threshold

Reflex is seen in both ears even if one is stimulated alone

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37
Q

How does the sensory side of the acoustic reflex circuit travel

A

Via CN VIII to ipsilateral ventral cochlear nucleus (VCN)

Output from the ventral cochlear nucleus then goes to the superior olivary complex on both sides of the brainstem which in turn projects to the facial nerve nuclei on their respective sides

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38
Q

Describe the a

efferent arm of the acoustic reflex circuit

A

Goes from the facial nuclei to enable contraction of the stapedius muscles in both ears

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39
Q

What is the main purpose of stapedius in birds

A

To reduce intensity of the sound produced when the bird cries/sings

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40
Q

What happens in a middle ear infection

A

Middle ear cavity filled with fluid and a low frequency hearing loss of 30 dB or greater may develop

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41
Q

In a middle ear infection Middle ear cavity filled with fluid and a low frequency hearing loss of 30 dB or greater may develop. What kind of hearing loss is this?

What is the other kind of hearing loss

A

Conductive loss

Sensorineural hearing loss (If the cochlear auditory pathway is damaged)

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42
Q

Name a test to distinguish between conductive and sensorineural hearing loss

A

Rinne test

The examiner place is a vibrating tuning fork alternatively on the mastoid process and at the entrance of the external auditory meatus

If the deafness is conductive bone conduction is unimpaired while the response to sound conducted by the external auditory meatus is reduced

If deafness is sensorineural detached shows a greater sensitivity to air-conduction at the external auditory meatus in comparison with bone conduction

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43
Q

What is the main structure of interest in the inner ear

A

Cochlea

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44
Q

What is the principal function of the cochlea

A

To decompose the acoustic signal into its component frequencies

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45
Q

How can the cochlea be considered functionally

A

Although it is coiled like a snail shell it can be considered as a straight tube compartmentalised longitudinally

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46
Q

Where do the scala vestiubli and scala tympani meet

A

At the helicotrema

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47
Q

Where is the scala media

A

A longitudinal partition between the scala vestbuli and scala tympani

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48
Q

What happens when stapes vibrates at the oval window

How is the cochlear partition (basilar membrane)designed

A

The incompressible fluids in the cochlea vibrate, causing the round window to bulge outwards

The cochlea partition is narrower and stiff it near its base than it’s apex and therefore vibrates Maximally for high frequency sound is near the base and maximally the low-frequency sounds near its apex

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49
Q

How are frequencies mapped out along the basilar membrane

A

Tonotopically along its length with equal increments in distance corresponding to equal increments in logarithmic frequency (mapping is non linear)

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50
Q

Describe the two types of hair cell in mammalian cochlea

A

1 row of inner hair cells (IHCs)

3 rows of outer hair cells (OHCs)

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51
Q

How many inner and outer hair cells are there

A

Inner ~ 3000

Outer ~ 11000

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52
Q

What are type 1 auditory fibres

A

The majority of auditory nerve fibres (90%) which synapse with the inner hair cells

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53
Q

What are type II fibres (hearing)

A

Unmyelinated cells that contact the outer hair cells and make up 10% of auditory nerve fibres

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54
Q

What are the two types of olivocochlear neuron

A

Medial olivocochlear neuron which projects to the outer hair cells

Lateral olivocochlear neuron which project to the primary afferents beneath the inner hair cells

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55
Q

Give 3 facts about basilar membrane vibration

A

Each point undergoes a sinusoidal vibration at the driving frequency

Max amplitude of vibration corresponds to the characteristic place on the cochlea’s frequency map

The pattern of vibration is not dependant on which end of the cochlea is stimulated

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56
Q

Does hearing change in death

A

Yes

Cadavers do not hear as well as humans

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57
Q

What are the agents if the mechanical feedback system in cochlear function

A

Outer hair cells

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58
Q

Name three lines of evidence to support the idea of outer hair cell active feedback

A

Many aspects of cochlear function or physiologically vulnerable

The ear can emit sound - otoacoustic emissions

Interruption of 0HC alters the IHT response

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59
Q

How do the outer hair cells change shape

A

Depolarisation causes length to decrease

Hyperpolarisation causes length increase

This allows accentuation of the sound vibration

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60
Q

Give the overall function of the inner and outer hair cells

A

Inner: Act to transducer the mechanical events in the cochlea to electrical events in the auditory nerve fibres

Alter: actively assist the mechanics of the cochlear and are responsible for sensitivity, sharpness of tuning and oto-acoustic emissions

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61
Q

In the cochlear physiological displacement of the stereocilia is caused by what

A

A relative movement between the reticular laminar and the tectorial membrane (OHCs) or by the flow of endolymph over the cilia (IHCs)

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62
Q

Where does transduction in hair cells take place

A

At the tips of the stereocilia

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63
Q

What happens if the stereocilia are stretch towards the tallest stereocilia?

What else will have this effect

A

The probability of the mechanically gated channels opening increases

If stretched towards kinocilium in the vestibular apparatus

64
Q

What happens if the stereocilia stretched away from the tallest stereocilia?

Where did this idea come from

A

The probability of the mechanically gated ion channels closing increases

The observation that the largest current changes occur near the tips of the stereocilia rather than at the base. The mechanical casing is thought to be controlled by tip links which connects the stereocilia

65
Q

How do the tip links of the stereocilia work

A

Stretching of the tip links, cause by displacing the bundle towards the largest stereocilia, is excitatory

Movement in the opposite direction is inhibitory

66
Q

What carries the transducer current in stereocilia?

What is the driving force

A

K+ ions

Entirely electrical

67
Q

What is the predominant cation in the endolymph

A

K+

68
Q

What is the resting membrane potential of the stereocilia cells

What is this couples to

Why is this arrangement important

A

-50mV

This is coupled with the large Endocochlear potential of +100mV

This gives a total gradient of 150mV

It means that few metabolic demands are placed on the hair cell to maintain its intra cellular composition – rather, active transport is needed to maintain the composition of the endolymph

69
Q

How is the composition of the endolymphatic fluid controlled

A

By the stria vascularis

70
Q

What is presbycusis?

A

The increasing of our hearing thresholds with age

71
Q

In men, are thresholds for higher frequencies poorer or better than for lower frequencies?

What about for women?

A

Thresholds for both men and
women are poorer in the high frequencies than
the lower frequencies.

72
Q

Hearing thresholds above which frequency are affected by ageing?

Why is this relevant to us ?

A

8Hz

this is not usually measured clinically

73
Q

What is the greatest factor affecting presbycusis?

A

the loss of the endocochlear potential arising from lateral wall degeneration with age

74
Q

How can we test the hypothesis that presbycusis is mainly due to loss of the
endocochlear potential arising from lateral wall
degeneration with age

A

s, it
is possible to selectively lower the EP in just one
ear by application of furosemide to the round
window. The resulting threshold loss seen with presbycusis
reduction in the EP mimics that seen

75
Q

Describe the hearing loss of presbycusis

A

a relatively flat loss at low
frequencies and a sloping loss at high
frequencies.

76
Q

What are OAEs?

A

otoacoustic emissions -sounds that
may be measured in the external auditory
meatus

77
Q

What evokes OAEs

A

sound

may occur spontaneously - evidence of the active process in hearing

78
Q

How many people have spontaneous OAEs

A

about 50% of

normal hearing humans have these

79
Q

What are Distortion product evoked otoacoustic

emissions (DPOAEs)

A

generated with the
presentation of two tones (aka the primaries, f1
and f2) and the largest of these emissions occurs
at the frequency 2f1 – f2

80
Q

What are OAEs like in patients with sensorineural hearing loss

A

Patients with a

significant sensorineural hearing loss lack OAEs.

81
Q

When is measurement of OAEs useful

A

in neonates where it is difficult to

establish the absence of hearing.

82
Q

What do IHCs release?

What does this act on

A

Glutamate from ribbon synapses

AMPAr on primary afferents (auditory nerve fibres)

83
Q

Where does adaptation to a tone burst occur in the hearing pathway

A

at the hair cell-afferent fibre synapse

84
Q

How can the output of the auditory nerve be considered

A

as a set of parallel, overlapping, bandpass

filters

85
Q

How do filters change for different frequencies in the nervous system?

A

narrower for higher frequencies

86
Q

What is the measure used to characterise filters in

a) engineering
b) to test hearing

A

a) Q3 dB

b) Q10 dB

87
Q

What is the characteristic frequency of a filter?

A

the most sensitive point of the filter

88
Q

True or false:
Tonotopicity is
preserved throughout the auditory pathway

A

true: from cochlear to cortex

this is spatial frequency mapping

89
Q

What is frequency resolution?

A

the ability to detect one
frequency component of a multi-frequency
complex stimulus, when all components are
presented simultaneously

90
Q

When is frequency sensitivity determined?

A

at the level of the basilar membrane

91
Q

Is there a relation between the psychophysical

bandwidths and the neural bandwidths recorded

A

Yes - a strong positive correlation between equivalent bandwidth and CF on a double log graph

92
Q

Do some auditory neurons have a preference for when they fire

A

yes
Low frequency auditory neurons discharge at
preferred phases of the stimulating signal.

93
Q

Do phase locked neurons fire every cycle?

A

No but when they do fire they fire at the same point (phase) of the wave

94
Q

What is the upper limit for phase locking for different animals

A

cat - 5000Hz
guinea pig - 3500Hz
Barn owl -8000Hz

95
Q

Why might you think 1000Hz is the upper limit for phase locking

A

it is the upper limit of spike discharge as set by the refractory period

96
Q

How can auditory nerve fibres be divided

A

groups based on their spontaneous discharge

rate

97
Q

What is spontaneous discharge rate defined as

A

defined as the discharge rate of an
auditory neuron in the absence of controlled
acoustic stimulation

98
Q

Which auditory fibres have the highest spontaneous discharge rate?

A

those with the lowest threshold (the most sensitive)

99
Q

What does the threshold of an auditory fibre determine?

A

its dynamic range

100
Q

which auditory nerve fibres have a narrow dynamic range

A

Low threshold
fibres have the narrowest dynamic range, high
threshold fibres have the widest dynamic range.

101
Q

What underlies our ability to perform discrimination of
small intensity differences over a wide range of sound
levels.

A

Of course, no
individual fibre can encode the entire range of sound
levels (> 100 dB) but combining the information from
the different fibre groups and an increase in the
number of active fibres at high sound levels allows discrimination

102
Q

What does the olivocochlear efferent system supply?

How is it divided?

A

descending
fibres from the superior olive to the cochlea.

It is
divided into two - lateral and medial

103
Q

Describe the lateral division of the olivocochlear system

A

has its cell bodies in or around
the lateral superior olive (depending on the
species

terminates on the dendrites
of the auditory nerve fibres

104
Q

Describe the medial division of the olivocochlear system

A

has its cell bodies
medial to the lateral superior olive, in the periolivary region of the superior olive

directly contacts the outer hair cells.

105
Q

What is the advantage of having both a medial and lateral division of the olivocochlear

A

The
brain is therefore able to influence the output of
both sets of receptor cells.

106
Q

What is the role of the lateral olivocochlear system?

A

unknown

107
Q

What are the 3 main hypotheses concerning the role of the medial olivocochlear system

A

protection from loud sounds

improving detection of sounds in noise (anti-masking)

controlling cochlear mechanics

108
Q

Describe the hypothesised role of the medial olivocochlear system in protection from loud sounds

A

If loud tone exposure is accompanied by electrical stimulation of the
medial olivocochlear system, the following increase in
threshold is greatly reduced.

109
Q

What is temporary threshold shift

A

an increase in threshold following exposure to a loud tone

110
Q

when is a protection from an increase in threshold seen

When is this disrupted

A

when the
exposure to a loud stimulus in one ear is
accompanied by an acoustic stimulus in the
other ear.

if the
medial olivocochlear system is disrupted

111
Q

How could you disrupt the olivocochlear system

A

. by
sectioning the olivocochlear bundle at the floor
of the fourth ventricle.

112
Q

What does anti masking mean

A

Electrical stimulation of the medial olivocochlear
system can improve the detectability of signals
in noise.

113
Q

What happens to detection and discrimination of vowel sounds when the olivocochlear bundle is cut?

A

detection
of vowel sounds is left intact when the
olivocochlear bundle is cut but
discrimination is impaired

114
Q

What is masking?

A

the process by which the threshold of hearing for one sound is raised by the presence of another sound.

115
Q

What is Auditory masking in the frequency domain known as

A

simultaneous
masking, frequency masking or spectral masking (i.e. a sound in one
frequency blocks the perception of another sound in another frequency, both occuring at the same time).

116
Q

What is masking in the temporal domain known as

A

temporal masking or non-simultaneous masking (i.e. an earlier
sound blocks the perception of a later occuring sound).

117
Q

How does antimasking work

A

Middle ear muscle reflex (MEMR) and Medial OlivoCochlear Reflex (MOCR) react to
sustained sounds and dampen them (the MEMR by stiffening the ossicle chain, which will dampen especially low-frequency sounds, the MOCR by reducing the responsiveness of the outer hair cells), so that any quieter sound has a better chance of getting heard (or is getting
“de-masked”).

118
Q

When do the 2 antimasking reflexes work best

A

both reflexes are effective in different (but slightly
overlapping) frequency ranges - the MEMR works better at lower frequencies 20-1000 Hz while the MOCR works better at higher frequencies, conveniently starting at about 1 kHz

119
Q

How does the medial olivocochlear system control cochlear mechanics

What would this require?

A

(i) Change the stiffness of the stereocilia or
(ii) Actively displace the stereocilia, introducing a
bias in their displacement

the cochlea to signal any changes in its
state to the brain

120
Q

What may signal changes in the state of the cochlear to the brain after it has been affected by the medial olivocochlear system

A

The type II auditory nerve

fibres (connecting with the OHCs)

121
Q

What is the purpose of the Medial olivocochlear system changing the cochlear mechanics

A

to keep the

cochlea in its optimal mechanical state.

122
Q

What is the reason for the auditory pathway being more complex than the visual pathway between the receptor and cortex

A

the need to compute the
localisation of a sound source from the receptor
epithelium which is tonotopically and not
spatially organised

123
Q

What is the cochlear nucleus

A

an
obligatory synapse for all auditory-nerve fibres
and has been described as the ‘retina of the
auditory system’.

124
Q

where does most parallel processing in the auditory system occur

A

cochlear nucleus

125
Q

Which cells are characterised by large end-bulb of Held synapses

A

cells in the cochlear nucleus specialised to
preserve the timing information present in the
auditory nerve input.

126
Q

What are the largest synapses in the brain

A

end-bulb of Held synapses

127
Q

Describe the different types of cells at the cochlear nucleus

A

timing preservation cells
intensity encoding cells
laterally inhibiting cells

128
Q

Describe the intensity encoding cells of the cochlear nucleus

A

have a dynamic range considerably
wider that found in any individual auditory nerve
fibre;

cells at this stage are summing

129
Q

Are any auditory pathway responses preserved as high as the cortex?

A

While much of the cochlear output may be
modified by the cochlear nucleus and higher
levels in the auditory pathway many response
properties of auditory-nerve fibres e.g.
tonotopicity, are preserved at levels as high as
the cortex

130
Q

Where is the first site of binaural convergence of the cochlear nucleus output?

A 
the superior
olivary complex (SOC)
131
Q

Describe the STRUCTURE OF THE SOC

A

There are three main
SOC nuclei; the lateral superior olive (LSO), the
medial superior olive (MSO) and the medial
nucleus of the trapezoid body (MNTB or MTB)

132
Q

What does the auditory midbrain consist of

A

the inferior

colliculus (IC) and the superior colliculus (SC).

133
Q

Describe the function of cells in the inferior colliculus

A

spatially selective, but no map of auditory space has been found in this nucleus.

134
Q

Describe the function of cells in the superior colliculus

A

a map of
auditory space does exist in the deep layers of
the superior colliculus and is usually aligned with
a visual map of space

135
Q

How is the primary auditory cortex (A1) organised

A

tonotopically organised and is
bordered by one or more adjacent auditory
areas.

136
Q

What is the function of the mammalian auditory cortex

A

no idea

137
Q

How is auditory space mapped on the basilar membrane

A

IT IS NOT

138
Q

How well can we discriminate the location of sounds in azimuth and in elevation

A

2°apart
in azimuth (or horizontal plane) and 10° apart in
elevation (or vertical plane)

139
Q

How does the intensity of a sound change with distance

How does this help most mammals calculate distance?

A

intensity of a sound decreases with distance
(amplitude decreases by a factor of 2, or 6 dB,
with a doubling of distance)

we are unable to use
intensity as a cue for calculating distance. We
would need to know the level of the source for
this to be a useful cue

140
Q

Can humans use intensity to localise sound?

A
  • in fact we are able to do
    this with limited success with human speech as
    we are so familiar with it
141
Q

Can you localise sound with one ear?

A

While sound
localisation is possible with one ear better
results are obtained by combining information
from the two ears. The brain can compare the
differences in both time and intensity of a sound
arriving in both ears.

142
Q

Which is the only location that sound travels equal distance to reach either ear

A

0° azimuth

143
Q

What is the maximum time difference between sound hitting one ear and the other in humans

What location would this occur at

A

660 microseconds

90° & 270° azimuth

144
Q

What is the minimum interaural time difference

A

10 microseconds

145
Q

How can interaural phase differences provide a cue for localisation

A

For continuous sounds below

about 1.4 kHz

146
Q

Why is 1.4kHz the limit for use of interaural phase difference in localisation

A

the
size of the head causes phase to become
ambiguous.

147
Q

Give an overview of neural encoding of interaural time differences

A

The MSO receives input from spherical bushy
cells of the anteroventral cochlear nucleus from
both sides of the brain and uses the
principles of coincidence detection and delay
lines to measure interaural time differences in
different frequency bands.

148
Q

What is the concept of delay lines? (4)

better described visually so there is also an anki card on this

A

neurons fire maximally when action potentials from the left and right ear arrive simultaneously.

Each neuron is maximally sensitive to a single time disparity (best ITD) and
different neurons are selective for different
disparities.

The axonal path to the neurons increases systematically along the array but in the opposite direction for the two ears.

Therefore, the place of a neuron in the MSO
signals the ITD to which the neuron responds best

149
Q

How can interaural intensity differences be used in localisation

A

At high frequencies the more distant of the two
ears is shadowed by the head and the sound
reaching this ear is less intense.

150
Q

What is the range for interaural intensity differences

A

The interaural
intensity difference is insignificant below about
1 kHz and reaches a maximum of about 20 dB for
high frequencies at 90° and 270°azimuth

151
Q

Describe the neural pathway to encode interaural intensity differences (give both inhibitory and excitatory pathways)

A

The LSO receives excitatory input from bushy
cells in the ipsilateral VCN and inhibitory input
from the ipsilateral MNTB.

The ipsilateral MNTB
receives excitatory input from the bushy cells of
the contralateral VCN

152
Q

What are cells in the MNTB characterised by

what does this allow

A

giant synaptic
endings allowing for the fast, precise
transmission of temporal information

153
Q

What does output of neurons in the LSO reflect in the hearing system?

A

the balance of ipsilateral excitation and contralateral inhibition

154
Q

For pure tones, what does localisation in the azimuthal plane depend upon

A

interaural time differences at low frequencies
and interaural intensity differences at high
frequencies

155
Q

for pure tones it appears that
localisation in the azimuthal plane depends on
interaural time differences at low frequencies
and interaural intensity differences at high
frequencies
What is this known as?

A

duplex theory

NHB (17 decks)

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