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PHGY314 > Auditory system > Flashcards

Auditory system Flashcards

1
Q

how many newborns have a hearing disorder?

A

4-6 out of 1000 (most common congenital illness)

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2
Q

why is hearing loss irreversible?

A

there is no regeneration of hair cells once they die

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3
Q

what % of adults have hearing impairment?

A

40% of adults over 75

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4
Q

what are the 2 universal newborn hearing screening?

A
  1. otoacoustic emissions
  2. auditory brainstem response
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5
Q

what is otoacoustic emissions test?

A

you put a speaker in babie’s ear and pick up the sounds that come out of the hair cells

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6
Q

what is auditory brainstem response test?

A

a more detailed test with electrodes on the forehead and on the auditory brainstem behind the ear

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7
Q

why is auditory brainstem response test better than otoacoustic? 2 reasons

A
  • babies often have fluid in their ear, making the otoacoustic test unreliable
  • auditory brainstem responses tells you that the whole auditory pathway is functional
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8
Q

what do vestibular hair cells respond to?

A

linear acceleration

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9
Q

what part of the ear is fluid filled

A

inner ear only

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10
Q

what frequencies activate cochlear vs vestibular hair cells?

A

vestibular hair cells are more sensitive to lower frequenceis

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11
Q

what is in the middle ear?

A

ossicles, between tympanic membrane and middle ear

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12
Q

what is the pitch of a sound?

A

the frequency of the sound

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13
Q

what level are audible frequencies?

A

20-20 000 Hz

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14
Q

what is the loudness of a sound? what can we hear?

A

the amplitude of the wave.
range 0.002 to 2000 dynes/cm^2

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15
Q

frequency response is determined by what?

A

the functional anatomy of the ear

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16
Q

what frequencies are human voices? (we are most sensitive to these frequencies)

A

500-5 000 Hz

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17
Q

what do decibels represent?

A

Weber-Fechners Law: decibels represent sound intensity in a way that corresponds to perceived loudness

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18
Q

what is Weber-Fechners Law formula?

A

L (loudness) = 20 x log10 (P/Pstd)
where P/Pstd = pressure / minimum pressure

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19
Q

where does auditory mechano-electrical transduction happen?

A

inner ear

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20
Q

what is the external auditory meatus?

A

auditory canal in external ear

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21
Q

what is the meatus function?

A

resonate the sound waves to ensure reliable transmission of speech (frequencies aren’t amplified, they just loose less energy)

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22
Q

what does the eustachian tube connect?

A

the middle ear to the pharynx

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23
Q

blocked eustachian tube can lead to what?

A

otitis media (middle ear infection from build up of fluid that slows down the ossicles)

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24
Q

is the eustachian tube normally open or closed?

A

normally closed; it opens during yawning to equilibrate pressure

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25
Q

name the 3 ossicles in order from tympanic membrane to the oval window

A

Malleus, Incus, Stapes

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26
Q

what are the 2 mechanisms of sound amplification? by how much do they each amplify the sound?

A
  1. mechanical amplification by ossicles: 1.3x increase
  2. pressure amplification from large tympanic membrane to smaller oval window: 17x amplification
    - together = 1.3 x 17 = 22x apmplification
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27
Q

why do we need such a sound amplification?

A

can’t hear without that because the fluid in the cochlea is so much denser than the air that all the energy would be lost

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28
Q

remember: pressure = ?? / ???
how does this apply to tympanic membrane and oval window?

A

pressure = force / area
tympanic membrane is 50 mm2, oval window is 3mm2 -> smaller area = bigger pressure

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29
Q

how does the MIDDLE EAR protect us from loud sounds?

A

muscles that limit motion of the ossicular chain:
- tensor tympani (malleus)
- stapedius (stapes)

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30
Q

when do the 2 middle ear muscles activate? give examples

A

activate reflexively for sounds above 80 dB, ex during chewing, or when a truck honks

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31
Q

to what frequencies is the external vs the middle ear sensitive to?

A

external ear: 2000 - 5000 Hz
middle ear: 500 - 2000 Hz

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32
Q

describe the cochlea

A
  • 33 mm long coiled structure that makes 2.5 turns
  • 3 fluid-filled compartments
  • sensory transduction at the Organ of Corti
  • basilar and tectorial membranes
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33
Q

what is found on the basilar vs tectorial membrane?

A

basilar = receptor cells
tectorial = stereocilia

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34
Q

what are the 3 fluid-filled compartments of the cochlea called?

A

scala vestibuli, scala media (cochlear duct), scala tympani

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35
Q

what media are found in endolymph vs perilymph? describe them

A
  • Endolymph → similar to intracellular fluid, found in scala media. high K+ + 80 mV than perilymph – produced by cells in stria vascularis
  • Perilymph → similar to extracellular fluid, high Na+ found in scala vestibuli, and scala tympani
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36
Q

how many hair cells do we have and how are they distributed?

A

16 000 cells per ear: 3 500 inner hair cells, 12 000 outer hair cells

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37
Q

what are inner vs outer hair cells role?

A

inner: 1 row, send sensory info to CNS
outer: 3 rows, shape response and amplify it

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38
Q

what does the round window act as?

A

a pressure release

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39
Q

what is the motion along basilar membrane called? how big is it?

A

traveling wave: 150 nm in height

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40
Q

explain the trajectory of the pressure wave in the inner ear

A

oval window -> scala vestibuli -> basilar membrane traveling wave -> round window

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41
Q

describe the basilar membrane mechanical properties

A

the apex is elastic and responds to 20Hz sounds
the base is stiffer and responds to 20 000 Hz sounds
(place coding = tonotopy)

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42
Q

what does upward vs downward deflection of the basilar membrane cause?

A

upward deflection towards the tallest cilia = excitation
downward = inhibitions

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43
Q

do hair cells fire AP?

A

NO they produced GRADED POTENTIAL by releasin glutamate

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44
Q

what part of hair cells are in contact with the endolymph (+80mv)? why?

A

stereocilia on the apical membrane. if we bathed the whole cell in endolymph it would depolarize

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45
Q

what and where is the synaptic ribbon?

A

found at the synapse of the hair cell with the afferent nerve; helps to block out background firing

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46
Q

what links stereocilia?

A

cross-linked actin filaments

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47
Q

why are tight junctions between hair cells basolateral sides important?

A

separates endolymph (in which stereocilia bathe) and perilymph

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48
Q

steps of signal transduction happening in the hair cell?

A
  1. stereocilia deflection
  2. hair cell depolarization
  3. Ca2+ influx and glutamate release
  4. afferent nerve firing to CNS
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49
Q

what cranial nerve for afferent sending of auditory signal?

A

8 vestibulocochlear lol throwback anat

50
Q

what type of cells are hair cells?

A

neuroepithelium cells

51
Q

how many stereocilia do outer hair cells have?

A

only 3 rows

52
Q

where air hair cells found? what are they for in the other locations?

A
  • cochlea (sound)
  • semicircular canal organs (angular head movement)
  • utricle and saccule (detect linear acceleration)
53
Q

hair bundle displacement causes a change in what?

A

receptor potential (membrane potential)

54
Q

what causes the membrane potential change produced by hair bundle displacement?

A

opening (depol) or closing (hyperpol) of mechanoelectrical transduction channels

55
Q

how is the “problem” of saturation of hair bundles solved?

A

adaptation step during long stimulus allows the reset the channels opening and closing, so the same current can be produced as before adaptation

56
Q

how does adaptation of the hair bundle happens? explain

A

change in tension on the gating springs that link stereocilia together
- controlled by myosin motor that move according to calcium levels in the stereocilia
- ex: sound -> stereocilia move, channels open -> Ca+ flow in -> myosin attachment of tip link slides down the stereocilia to DECREASE the tension
- low calcium = myosin climbs and increase tension

57
Q

give 2 reasons why mechanical gating is better

A
  1. faster than second messengers (10s microsecond for hair mechanotransduction vs 10s milliseconds for phototransduction)
  2. speed is critical for hearing,
    a) sound of 100 kHz = hair bundle must move at 100 kHz = channels open and close at 100 kHz
    b) sound localization is based on temporal delay of sometimes 10 microseconds
58
Q

the basilar membrane is more finely tuned for what frequencies? how?

A

high frequency sounds:
- bundles at the base of the membrane are shorter and stiffer = higher freq
- bundles at the base have faster mechanically-gated channels

59
Q

what are the cochlear amplifiers?

A

hair cells

60
Q

much of the sound stimulus energy is needed to overcome what?

A

to overcome damping by the cochlear fluid

61
Q

what are spontaneous otoacoustic emissions?

A

In a quiet environment, human ears spontaneously emit pure tones

62
Q

what happens to the shape of the outer hair cells OHC themselves when depolarized/hyperpolarized? why?

A

depolarized = OHCs rapidly shortens
hyperpolarized = OHCs rapidly lengthen
- this increases the motion of basilar membrane which amplifies the receptor potential in inner AND outer HCs

63
Q

what are responsible for otoacoustic emmissions?

A

OHCs

64
Q

Reducing OHC function with efferent activation, drugs or ablation decreases what?

A

decreases cochlear sensitivity and frequency discrimination

65
Q

what is required for electromotility of OHCs?

A

Prestin: protein in walls of OHCs

66
Q

what does hypoxia do to OHC?

A

it eliminates OHC sharp tuning, making the sound pressure level passive response

67
Q

what is the evidence for the cochlear amplifier to exist?

A

evoked otoacoustic emissions: return sound contains different frequency components that could not be generated just by the mechanical shape of the tympanic membrane

68
Q

how many afferent nerves do we have par cochlea and how are they distributed?

A
  • 30 000 afferents per cochlea
  • 95% of afferent come from IHC (about 10 afferent per IHC)
  • 5% come from OHCs (multiple OHC per afferent)
69
Q

how are efferent distributed?

A

95% of efferent go to OHCs

70
Q

where do afferents go?

A

type I neuron -> 8th nerve -> cochlear nucleus in brainstem

71
Q

where are efferent cell bodies located?

A

in the superior olivary complex in the brainstem

72
Q

what do neurons coming from lateral vs medial olivary complex each do?

A
  • lateral OC neurons (5% of efferents) synapse on type I afferent neurons to decrease the brain’s own firing sound
  • medial OC neurons (95% of efferents) synapse on OHCs and depolarize them
73
Q

how does the afferent response adapt?

A

it declines over time to adapt for louder sustained sounds

74
Q

what happens to the firing rate of afferents when there is a pure tone and noise playing?

A

due to adaptation, the neurons responds less than when only a pure tone is played

75
Q

what role do efferents play in afferents response to sounds in noisy environment?

A

medial OC efferents increases the response of a neurons (brings operating range back to normal)

76
Q

sound perception by the brain relies on what information being extracted from the afferent?

A
  • which nerve fiber is activated
  • rate of spiking
  • temporal pattern of spiking
77
Q

why is afferent information from one INC not redundant?

A

frequency is tonotopically arranged in place code, each of the 10 afferent that come from one IHC can cover their own part of the amplitude to cover the whole 0 to 120 Db range together

78
Q

different afferent with the same characteristic frequency can cover the entire _______ range for a given frequency

A

amplitude

79
Q

afferent have different spontaneous rates. what does that change?

A

afferents with higher spontaneous rates fire more easily and therefore are more sensitive, need less sound energy to be activated

80
Q

what is the afferent response temporal code? explain

A

phase locking: neuron can not fire at every peak of a sound wave; so it fires at the same phase of the wave but not at each cycle

81
Q

why is phase locking most important for lower frequency sounds, if the waves of those sounds are faster??

A

because low freq sounds activate a wider area of the basilar membrane, therefore the place code is not as useful

82
Q

what is the sensitivity range of each type 1 afferent?

A

30 dB

83
Q

how is the loudness of a sound coded for?

A

increasing the firing rate of one afferent and recruiting additional afferents

84
Q

what is the cochlear amplifier?

A

outer hair cells lengthening / shortening

85
Q

most efferent contact which cells?

A

OHCs, some contact afferents

86
Q

where do efferents arise from?

A

Medial Olivary Complex of the superior olivary complex

87
Q

remember: where do efferent from the lateral olivary complex synapse?

A

on afferents

88
Q

the efferent control the gain of what?

A

the gain of the cochlear amplifier

89
Q

how is frequency vs loudness encoded by afferents?

A

frequency:
- high frequency encoded by location of basilar membrane that is maximally excited
- low freq encoded via temporal coding (phase locking)
loudness: number of spikes and recruitment of afferents

90
Q

explain the auditory pathway from afferent to auditory cortex

A

afferent -> cochlear nucleus in brainstem -> superior olivary nucleus -> inferior colliculus -> medial geniculate nucleus -? auditory cortex

91
Q

where does auditory information cross?

A

at the brainstem, same level as the cochlear nuclei

92
Q

give the characteristic of the cochlear nuclei

A
  • 3 subnuclei
  • each has an orderly tonotopic map
  • has different cell types with different response properties (different firing response)
93
Q

what part of the auditory pathway is responsible for sound localization?

A

superior olivary nucleus

94
Q

what are the 3 cues used for sound localization?

A

1) interaural time differences
2) interaural intensity difference
3) miniature echoes

95
Q

what part of the brain is responsible for computing interaural time difference? for what sounds can it be used?

A
  • medial superior olive
  • used to localize sounds below 1500 Hz
96
Q

what part of the brain is responsible for computing interaural level difference? for what sounds can it be used?

A
  • lateral superior olive
  • for sounds above 3000 Hz
97
Q

what cells in the cochlear nucleus mimic the auditory nerve fiber firing activity?

A

spherical bushy cells

98
Q

spherical bushy cell maintain what type of information?

A

timing information of the sound

99
Q

what are other names for auditory cortex?

A

Area A1 or Brodmann’s areas 41 and 42 on Heschl’s gyrus

100
Q

A1 has a tonotopic map of what characteristic of sound?

A

kiloHertz (frequency)

101
Q

neurons in what part of the auditory path have receptive field for locations?

A

auditory cortex A1

102
Q

most regions around the auditory cortex are involved in what?

A

speech processing and other unknown functions

103
Q

A1 is arranged in what?

A

columns

104
Q

what was the paper about?

A

recording from A1 neurons in rats to measure their frequency selectivity and see how noise exposure affected their auditory cortex development

105
Q

Previous experiments showed that playing 7 kHz tones during development led to overrepresentation of _____ _____ ____
but did not affect the ______ _______

A

7kHz cortical space;
critical period (11-13days development period)

106
Q

what were the results of the study?

A

Early (day 7) broadband noise exposure prevents refinement of tonotopic map

107
Q

then they tested if the noise just extended the critical period or actually altered the mature pattern of A1 (no tonotopic map forever). results?

A
  • played noise for 90 days: the auditory cortex remained plastic!
  • after the 90 days: rats were able to form a tonotopic map that overrepresented 7kHz because they listened to 7Khz sound after 90 days
108
Q

Normal sound exposure (p50-p120) after noise exposure (p7-p50) leads to what?

A

a normal A1 tonotopic gradient!

109
Q

give examples of conditions that could contribute to auditory and language-related delays in children

A
  • chronic otitis media
  • cleft palate that closes the eustachian tube
110
Q

Human critical period for auditory cortex development continues until what age?

A

6 to 7 years of age

111
Q

in human when does the perception of word sounds and syllables mature? what about word meaning?

A

sounds and syllables: 8-10 months
word meaning: 2-4 years

112
Q

how can speech processing be influenced by our sense of touch?

A

researchers at UBC showed that the puffs of air that accompany sounds starting with “p”, “t” and “k” influence our perception of sound.

113
Q

congenital deafness affects what % of the population?

A

0.1%; half of cases are genetic

114
Q

what is most age-related hearing loss caused by? what are other causes?

A
  • hair cells (cochlear) damage
  • genetics, bacterial meningitis, noise, ototoxic drugs (aminoglycoside antibiotics, cisplatin)
115
Q

how does our hearing range change through life?

A
  • newborn = 20 - 20 000 Hz
  • 20 yo: 20 - 16 000 Hz
  • retirement: 20 - 8 000 Hz
116
Q

what is presbycusis?

A

bilateral hearing loss

117
Q

what hair cells are most susceptible to damage?

A

OHCs

118
Q

what characteristic of sounds can be rescued by an hearing aid?

A

loudness, but not frequency selectivity

119
Q

what is conduction deafness?

A

sound can not get to the middle or inner ear
ex: wax accumulation, otitis media, otosclerosis (bones can’t move)

120
Q

what is sensorineural hearing loss?

A

damage to the organ of Corti or the 8th nerve
causes:
- persistent loud noises
- toxic drugs (streptomycin)
- old age
- tumors of VIII nerve
- infections

121
Q

what are 3 clinical tests for audition?

A
  • Audiometry: test with pure tones
  • Bone Conduction (Rinne test)
  • Otoacoustic Emissions

PHGY314 (9 decks)

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