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Week 12 > Physiology of hearing > Flashcards

Physiology of hearing Flashcards

1
Q

what is sound

A

vibration of a medium
spreads out as a wave of pressure
- any vibrating object creates pressure waves in the medium around it
pressure waves dissipate as you get further away

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2
Q

what are Hz

A

frequency in cycles/ sound

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3
Q

what is the range of human pitch hearing

A

20 - 20,000 Hz

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4
Q

how is intensity of sound measured

A

log ratio scale
dB (bels)
3dB = 2x sound energy
10 dB = ten times the sound energy/ twice the perceived loudnessw

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5
Q

what is threshold

A

the quietest sound that can be heard at each frequency

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6
Q

what is dB SPL

A

sound pressure log graph
sound pressure = 20 x log10 P/Pref

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7
Q

what is dB HL

A

dB SPL corrected by referencing actual sound pressure against hearing thresholds in YA with normal hearing

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8
Q

what are the components of the outer ear

A

pinna, ear canal

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9
Q

what are the components of the middle ear

A

tympanic membrane (TM), ossicles

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10
Q

what are the components of the inner ear

A

cochlea, vestibule

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11
Q

why do we have 2 ears

A

sound localisation in the horizontal plane
- inter-aural time difference
- difference in intensity

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12
Q

what is the function of the pinna

A

visible part of the ear
amplifies + filters incoming sounds
directional - dependant filtering at certain frequencies

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13
Q

what is the function of the ear canal

A

the resonance results in a 10dB (3x) increase in level for speech frequencies

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14
Q

what specialisations does the ear canal have

A

2.5 cm long
Hairs in the outer 1/3 to trap debris
earwax - antiseptic/ antifungal, traps debris
Skin - grows away from the drum and carries debris with it to the outside world

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15
Q

what is impedance mismatch

A

how do we get sound waves in the air to enter the fluid of the cochlear instead of bouncing off
- 99% of sound deflected by the surface of water

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16
Q

how do we overcome the impedance mismatch

A

collect sound energy over a large area -> TM
convert vibration of air (not very dense) int vibration of bone (dense)
concentrate all the energy onto a small area (oval window)
use the bone as a piston to transfer energy into the fluid

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17
Q

by how many times does the area ratio TM: oval window decrease and why

A

17 fold smaller
amplifies sound by concentrating energy
- 25 dB gain

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18
Q

where do the malleus and incus originate from (embryonically)

A

first brachial arch

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19
Q

where does the stapes originate (embryonically)

A

second brachial arch

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20
Q

what are the protective muscles in the ear

A

stapedius reflex
tensor tympani

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21
Q

what is the role of the stapedius reflex

A

involuntary contraction of the stapedius muscle in the middle ear to keep the ossicles steady, reducing the intensity of the sound

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22
Q

what is the role of the tensor tympani

A

located on the back of the eardrum to prevent it from breaking
protect against loud sounds

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23
Q

where is the Eustachian tube

A

connects the nasopharynx to the middle ear

24
Q

what is the purpose of the Eustachian tube

A

allows are to enter ad leave the middle ear
closed at rest, opens during swallowing and Valsalva manoeuvre (ears popping/ forcing air into middle ear)
keeps the air pressure in the middle ear space the same as the ambient atmospheric pressure

25
Q

why is important to keep air pressure inside the middle ear the same as atmospheric pressure

A

allows the TM to vibrate
dysfunction leads to blocked feeling and poor hearing (e.g. aeroplane flight)

26
Q

what is conductive hearing loss and how does it occur

A

problem with outer/ middle ear
- inner ear works fine
ear canal - wax, foreign body, congenital atresia
TM - perforation
ossicles - congenital fusion, damage from infection

27
Q

what is the treatment for conductive hearing loss

A

vibrate the skull - bone conduction
- hearing aids

28
Q

what are the two sensory structures in the inner

A

vestibular apparatus
cochlea

29
Q

what is the role of the vestibular apparatus

A

contains sensory structures for balance and head movements

30
Q

what is the role of the cochlea

A

contains sensory epithelium from hearing -> organ of Corti

31
Q

describe how vibrations get into the cochlea

A

1- oval window faces into vestibule
2- vestibule contains sensory epithelia for saccule and utricle
3- vestibule leads into scala vestibuli (upper cochlear duct)
4- pressure waves travel along scala vestibuli then back through scala tympani (lower cochlear duct)
5- waves terminate at the round window

32
Q

what is the saccule

A

a bed of sensory cells in the inner ear
translates head movements into neural signals for the brain to interpret

33
Q

what is the utricle

A

fluid-filled sac containing hair-like cells that translate head movements into neural signals for the brain to interpret

34
Q

what is the organ of Corti

A

sensory epithelium containing auditory hair cells

35
Q

what is the stria vascularis

A

regulates ionic and metabolic functions of the scala media

36
Q

what fluid is located inside the scala media

A

endolymph
- high in K
- low in Na

37
Q

what is the scala vestibuli/ tympani full of

A

perilymph
- ^ Na
- low K
more typical ECM

38
Q

how do we detect frequency

A

the basilar membrane
- stiff and light at one end
- flexible and heavy at the other end
- its resonant frequency changes over its length

39
Q

what is the structure of the hair cells in the ear

A

epithelial origin, resembles cells that line the stomach
stereocilia form bundle at apical pole of the hair cell
stereocilia arranged from shortest to tallest

40
Q

what happens when the stereocilia are pushed towards the tallest end

A

depolarisation
K+ channels opened, K+ flows into cells from the endolymph

41
Q

what happens when stereocilia are pushed towards the shortest end

A

hyperpolarisation
K+ channels opened

42
Q

what is the role of inner hair cells

A

turn vibrations into neural signals
- sent down afferent and lateral efferent neurons

43
Q

what is the role of outer hair cells

A

amplify vibrations
motile
1- when stimulated (by movement of basilar membrane) OHCs change shape + stiffness
2- feeds back energy into the basilar membrane (reverse transductions)
3- acts as an amplifier, increasing amount of vibration on basilar membrane (cochlear amplifier)
also improves frequency selectivity
transmits signals down medial afferent neuron

44
Q

what are otoacoustic emissions and what are they used for

A

OHC move in response to noise
we can hear them moving

quick, objetive screening test for hearing loss in babies

45
Q

what are hair cells vulnerable to

A

infections, ototoxins, noise
aging
sensorineural hearing loss

46
Q

what happens with loss of IHCs

A

no signal to the brain
all dB loss in hearing

47
Q

what happens with outer hairs cells

A

basilar vibration in insufficiently amplified
~50dB loss in hearing
loss of sound discrimination

48
Q

how do hearing aids work

A

make everything louder
microphone - amplifier - speaker

49
Q

in what situations are hearing aids helpful

A

conductive hearing loss
doesn’t solve sensorineural hearing loss -> loss of discrimination/ dynamic range/ central processing effects

50
Q

what are the two ways that pitch is encoded

A

place code
temporal code

51
Q

how does place code work

A

vibration of basilar membrane
accuracy limitation to place code
- wide region vibrates

52
Q

how temporal code work

A

phase locking to stimulus
upper frequency limitation to temporal code - neurons can only fire so quickly

53
Q

what is the clinical relevance of coding mechanisms in the ear

A

possible to put a hearing implant directly into the cochlea to stimulate the spiral ganglion of cells if there is a severe hearing loss due to loss of hair cells
cochlear implants have been revolutionary for congenital and acquired sensorineural loss

54
Q

describe the sequence of sound processing

A

1- first order neurons in the spiral ganglion of the cochlea
2- travel in the CN VIII through internal acoustic meatus to cerebello-pontine angle
3- synapse on cochlear nuclei (junction of medulla and pons)
4- via olive and trapezoid body (pons) to inferior colliculus (midbrain)
5– medial geniculate body (thalamus)
6- superior temporal gyrus (cortex)

55
Q

when would you put a hearing implant directly onto brainstem

A

cochlear nucleus in the brainstem if there is no auditory nerve (after resection of a tumour in the nerve) but results aren’t great
damage in the CNS (stoke) doesn’t tend to produce hearing loss because, above the cochlear nuclei representation is bilateral

Week 12 (3 decks)

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