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sensory systems > the ear and sound detection > Flashcards

the ear and sound detection Flashcards

1
Q

what is sound?

A

the displacement of air that creates regions of compressed air (peaks) and rarefied air (troughs)

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2
Q

what is the speed (velocity) of sound at room temperature?

A

343 m/s

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3
Q

calculate velocity

A

frequency x wavelength

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4
Q

what is frequency

A

number of peaks per second (in Hz) (number of compressed areas per second)

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5
Q

what is a wavelength

A

distance between successive peaks (in m)

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6
Q

relationship between frequency and wavelength

A

lower frequency= longer wavelengths
higher frequency = shorter wavelengths

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7
Q

intensity

A

higher displacement of air but the same frequency

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8
Q

outer ear

A

pinna, auditory canal and tympanic membrane

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9
Q

middle ear

A

malleus, incus, stapes and oval window

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10
Q

inner ear

A

cochlear

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11
Q

sound pathway from the pinnae to the oval window

A

1) sound waves travel through air down the auditory canal, displacing the tympanic membrane
2) tympanic membrane pushes on the handle of the malleus
3) the malleus acts as a lever with a fulcrum point that is nearer to the handle, as the handle is displaces to the right, the head is displaced to the left
4) malleus passes the movement to the incus, the incus to the stapes, and the stapes to the oval window

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12
Q

what does the lever effect have on the oval window?

A

pressure at the oval window is increased 20x

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13
Q

how many muscles are there in the inner ear? what are they attached to?

A

two muscles, one attached to the malleus and one attached to the stapes bone

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14
Q

what happens when muscles in connected to the malleus and stapes contract?

A

they stiffen the ossicles and dampen the intensity that enters the inner ear via the oval window

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15
Q

intensity and frequency the attenuation reflex is needed at

A

High intensity (>60dB) Low frequency (<2,000Hz)

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16
Q

what is the attenuation reflex?

A

feedback mechanism to dampen loud sounds and protect hair cells in the inner ear

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17
Q

pathway when the inner hair cells are being put under too much mechanical pressure

A

inner hair cells
project to the posterior ventral cochlear nucleus (PVCN)
projects to the superior olivary complex

1)
projects to the facial motor nucleus (cranial nerve 7)
contracts the stapedius muscle

2)
projects to the NLL
projects to the motor 5 nucleus (cranial nerve 5)
contracts the muscle attached to the malleus

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18
Q

pathway of internally generated sounds

A

motor V nucleus
cranial nerve 5
contracts muscle attached to the malleus

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19
Q

what three chambers are found in the cochlear

A

scala vestibuli
scala media
scala tympani

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20
Q

which chambers is perilymph found?

A

scala vestibuli
scala tympani

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21
Q

which chambers is endolymph found?

A

scala media

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22
Q

endolymph composition

A

1mM Na+ low
150mM K+ high

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23
Q

why does the endolymph have high K+ and low Na+?

A

due to ion transport by stria vascularis cells

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24
Q

why is the composition of endolymph in the scala media important?

A

high level of potassium outside of hair cells allows it to move down the concentration gradient into the cell

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25
Q

perilymph composition

A

low K+ and high Na+
like extracellular fluid

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26
Q

where is the organ of corti located

A

on the basilar membrane, between the scala media and scala tympani

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27
Q

where is the basilar membrane?

A

between scala tympani and scala media

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28
Q

where is reissner’s membrane?

A

between scala vestibuli and scala media

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29
Q

where is the stria vascularis

A

in the scala media

30
Q

what happens when the stapes taps on the oval window?

A

it causes displacement of the perilymph

31
Q

what chambers are continuous with each other?

A

scala vestibuli and scala tympani

32
Q

what does vibration of the basilar membrane determine?

A

how the hair cells in the organ of corti are going to be bent, determining if they open

33
Q

where will high frequency sound vibrate the basilar membrane?

A

closer to the base, and will quickly be dampened

34
Q

where will low frequency sounds vibrate the basilar membrane?

A

allow the basilar membrane to vibrate to the apex

35
Q

structural features of the basilar membrane

A

thicker and stiffer at the base
thinner and floppier at the apex

36
Q

where are hair cells found?

A

the organ of corti

37
Q

frequency and the basilar membrane

A

each frequency causes a maximal displacement at a particular region along the membrane

38
Q

outer hair cells structure

A

have their stereocilia buried in the reticular lamina

39
Q

inner hair cells structure

A

have free stereocilia that sit below the tectorial membrane

40
Q

mechanical displacement of hair cells

A
  • When basilar membrane is deflected up the stereocilia bend outward
  • Deflection of the stereocilia in one direction increases receptor potential (depolarisation)
  • Deflection of the stereocilia in the opposite direction decreases receptor potential (hyperpolarisation)
41
Q

depolarisation of inner hair cell

A
  • The tips of the stereocilia have mechanically gated TRPA1 ion channels
  • When the stereocilia bend these open
  • Endolymph has high K+ so potassium floods into the hair cell
  • This depolarises the cell and opens voltage gated Ca2+ channels
  • Calcium influx
  • Neurotransmitter release
  • Activate spiral ganglion neuron
42
Q

movement of potassium at resting inner hair cell

A

leaky movement into hair cells

43
Q

channel inner hair cells

A

TRPA1

44
Q

inner hair cells to spiral ganglion

A

one inner hair cell to many spiral ganglion cells
well innervated

45
Q

outer hair cells to spiral ganglion cells

A

many outer hair cells to one spiral ganglion cell
poorly innervated

46
Q

what intensity activates more spiral ganglion cells

A

higher intensity

47
Q

spiral ganglion cells with high spontaneous activity require…

A

lower frequency to up the signal to threshold for them to respond

48
Q

spiral ganglion cells that have low spontaneous activity require

A

a higher frequency to reach threshold for them to respond

49
Q

high spontaneous rate = x threshold

A

low

50
Q

low spontaneous rate= x threshold

A

high

51
Q

high spontaneous rate SGNs fire from

A

0dB up to ~20dB saturation

52
Q

medium spontaneous rate fire from

A

~20dB to ~40dB saturation

53
Q

low spontaneous rate fire from

A

~40dB to ~80dB

54
Q

what frequencies are coded by low, mid and high spontaneous rate spiral ganglion cells? what organisation is this?

A

4000Hz and above (high frequency)
tonotopic organisation

55
Q

what happens as you increase frequency

A

basilar membrane vibration will increase to reach the particular area

56
Q

how do spiral ganglion cells respond below 4000Hz

A

they phase lock their firing to frequency instead of the intensity

57
Q

what is volume coded by >4000Hz

A

SGN firing rate and number of activated SGNs

58
Q

what cells act as a cochlear amplifier?

A

outer hair cells

59
Q

what protein allows outer hair cells to elongate or compress?

A

the motor protein prestin

60
Q

what happens when an outer hair cell is activated?

A

K+ influx activates motor proteins that compress the cell
this amplifies the basilar membrane movement and leads to an increased bending of the inner hair cell stereocilia

61
Q

how much do outer hair cells amplify the basilar membrane movement

A

x100

62
Q

when is the medial olivocochlear reflex inhibition used? why

A

High intensity, high frequency (>2,000Hz)
Loud high frequency noise activates reflex descending (effector) circuits to dampen sound input to protect the hair cells from mechanical damage

63
Q

medial olivocochlear reflex mechanism/ pathway

A

inner hair cells
project to posterior ventral cochlear nucleus (PVCN)
project to ventral nucleus of the trapezoid body’s (VNTB) medial olivocochlear system (MOCS)
cranial nerve 8 projects to the outer hair cells
acetylcholine hyperpolarises OCHs to relax prestin, elongating the cells and pushing the basilar membrane down

64
Q

result of elongation of outer hair cells

A

dampens the outer hair cell amplifier causing less displacement of the inner hair cell stereocilia

65
Q

conductive hearing loss

A
  • Defect in outer or middle ear
  • Checked using Rinne’s test
  • Each ear is tested separately, check if there is conductive impairment in each ear
66
Q

sensorineural hearing loss

A
  • Defect in inner ear (cochlear or auditory nerve)
  • Checked using Weber’s test
  • Comparison between ears (lateralisation test)- can detect if one ear is more impaired than the other
67
Q

Rinne test

A

place the base of struck tuning fork on the mastoid bone

have patient indicate when the sound is no longer heard

now move the fork beside the ear an ask if it is audible

68
Q

conclusion of rinne test

A

if patient can hear the fork at their ear they have normal hearing

if the patient cannot hear the fork at their ear they have conductive hearing loss

69
Q

weber test

A

place base of struck tuning fork on the bridge of forehead, nose or teeth

70
Q

results of weber test

A

normal: no lateralisation
unilateral conductive loss: lateralisation to affected side
unilateral sensorineural loss: lateralisation to normal or better hearing side

71
Q

audiogram shows

A

the hearing level for each ear at various levels

sensory systems (17 decks)

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