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Biology 404 > Auditory system > Flashcards

Auditory system Flashcards

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1
Q

The human auditory system can distinguish between these 2 properties of sound

A

Frequency and amplitude

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2
Q

Describe the rate of response of the auditory system (fast/slow)

A

Fast

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3
Q

What is the general purpose of the auditory system for survival?

A

Orient the head and the body towards novel stimuli as an “early warning system”

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4
Q

What is sound?

A

A wave of mechanical energy produced by moving air molecules

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5
Q

What is upper limit of the range of human auditory detection in volume level? (decibels)

A

Just over 120-140 decibels

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6
Q

Describe wave frequency

A

The number of cycles in a second

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7
Q

Musical tone is made up of…

A

One fundamental frequency or pitch, but it is not perfect

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8
Q

An octave increase corresponds to this increase in frequency

A

2-fold increase

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9
Q

Describe the characteristic frequency of background noise

A

No characteristic frequency

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10
Q

What frequencies of sound can human ears detect?

A

20-20,000 Hz

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11
Q

Sound above the frequency of human detection is called…

A

Ultrasound

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12
Q

Sound below the frequency of human detection is called…

A

Infrasound

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13
Q

As we age, how does sound perception tend to change?

A

Lose sensitivity to higher frequencies

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14
Q

What are 3 examples of animals which can hear sounds higher than humans?

A

Dogs, Dolphins, mice

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15
Q

If an animal has a lower range of sounds for communications, what would this be useful for?

A

Communicating over long distances

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16
Q

Auditory neurons are derived from this sensory placode

A

Otic placode

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17
Q

Which germ layer do hair cells originate from?

A

Ectoderm

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18
Q

What structures make up the outer ear?

A

The pinna, auditory canal, tympanic membrane

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19
Q

Which structures make up the middle ear?

A

Ossicles and oval window

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20
Q

Which of the ossicles is connected to the tympanic membrane?

A

Malleus

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21
Q

What is the order of the ossicles starting at the tympanic membrane?

A

Malleus > incus > stapes

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22
Q

The middle ear is filled with…

A

Air

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23
Q

The inner ear (cochlea) is filled with…

A

Fluid

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24
Q

What is the name of the tube which connects the middle ear to the nasal cavities?

A

Eustachian tube

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25
Q

Describe how middle ear infection can cause conductive hearing loss

A

Accumulation of scar tissue from infection can immobilize the bones

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26
Q

Is conductive hearing loss permanent?

A

No, it can often be repaired

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27
Q

Describe Rinne’s test

A

Activate a tuning fork, hold next to ear and then nearby ear with tuning fork on a bony surface (skull)

If you can only hear when the fork is directly against the skull, the person has conductive hearing loss

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28
Q

Hearing aids would be beneficial to someone who…

A

Still has functional hair cells, just fewer of them

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29
Q

Cochlear implants would be beneficial to someone who…

A

Has a hair cell defect

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30
Q

What structures are in the inner ear?

A

Cochlea

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31
Q

What are the 2 key roles of the inner ear?

A
  1. Deconstruct complex sounds into constituent sounds
  2. Confines the action of each component tone to a discrete segment of the cochlea (tonotopic map)
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32
Q

The apex of the cochlea is called…

A

Helicotrema

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33
Q

The membrane in the middle of the cochlea is called the…

A

Basilar membrane

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34
Q

What are the names of the fluid in:
1. The scala vestibuli
2. The scala tympani and media

A
  1. Perilymph
  2. Endolymph
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35
Q

Where is the round window?

A

Below the oval window

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36
Q

Where are hair cells located in the inner ear?

A

On the basilar membrane

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37
Q

The basilar membrane is (wider/narrower) at the apex than at the base

A

Wider

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38
Q

High frequency sounds are detected at the (apex/base) of the cochlea

A

Base

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39
Q

Low frequency sounds are detected at the (apex/base) of the cochlea

A

Apex

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40
Q

Describe the stiffness of the cochlea at the base and the apex

A

Stiff at base, floppier at the apex

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41
Q

Describe what is meant by tonotopic map

A

The inner ear arranges vibrational frequencies on the basilar membrane

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42
Q

Describe the role of the tectorial membrane

A

Overlies hair cells and moves with vibration to allow hair cells to be deflected and open

43
Q

Are outer or inner hair cells more important for the detection of sound?

A

Inner

44
Q

What is the organ of corti?

A

Structure along the basilar membrane which is made of hair cells and supporting cells

45
Q

Describe the formation of outer hair cells

A

Form little V’s in rows

46
Q

Are there more outer hair cells or inner hair cells in an ear?

A

Outer hair cells more abundant

47
Q

Do hair cells have axons?

A

No, synapse to ganglion cells

48
Q

When hair cells are lost, can they be replaced?

A

No

49
Q

What neurotransmitter do hair cells release in response to activation?

A

Glutamate

50
Q

What is the proposed role of outer hair cells?

A

Might contribute to amplification of sound or protection (moving tectorial membrane so that hair cells are not activated at high volumes)

51
Q

Describe the input/output of outer hair cells

A

Few input and a lot of output

52
Q

Inner hair cells connect to (a single/multiple) spiral ganglion cells

A

Multiple

53
Q

Describe stereocilia

A

The little staircase projections on the tops of hair cells which contact the tectorial membrane

54
Q

Describe kinocilia

A

Large stereocilia which disappear in adult hair cells in humans

55
Q

What structure connects the stereocilia of the hair cells to each other?

A

Tip links

56
Q

Describe the arrangement of stereocilia on the apical surface of a hair cell

A

Staircase arrangement: arranged from shortest to tallest

57
Q

When stereocilia are bent in one direction, what happens?

A

If bent enough to reach threshold, the cell will depolarize

58
Q

In hair cells, describe how mechanical energy is transformed into electrical energy

A

Vibrations of the fluid move the basilar membrane, pushing the stereocilia of the hair cells over to one side and causing channels to open, depolarizing the cell

59
Q

What initiates bending of the stereocilia?

A

Upward motion of the basilar membrane

60
Q

Describe how hearing aids can be customized

A

If a person is struggling with hearing specific frequencies, the hearing aids can amplify only those frequencies

61
Q

Describe a cochlear implant

A

An electrode with frequency bands is inserted into the cochlea surgically, it detects certain frequencies and stimulates the basilar membrane in the area which corresponds with that frequency

62
Q

Where does a cochlear implant get inserted within the cochlea?

A

Along the scala tympani

63
Q

What is Usher syndrome?

A

Loss of visual and auditory input - mutation in a gene common to both systems

64
Q

Describe the mutation in Usher syndrome

A

Mutation in the tip links of hair cells and cilia of rod photoreceptors - results in supporting cells of the retinal pigmented epithelium not being able to support photoreceptors

65
Q

In a person with complete loss of hair cells, what 3 treatment approaches are available?

A

Cochlear implants
Stem cell replacement therapy
Gene therapy

66
Q

What are three key requirements in cell replacement therapy?

A
  1. Cells need to have the correctly specified fate
  2. Cells need to be incorporated at the correct location
  3. Cells need to integrate into the correct circuit
67
Q

Describe endogenous stem cells

A

Adult supporting cells which are induced to become stem cells

68
Q

What are 2 exogenous sources of stem cells?

A

Embryonic stem cells
Induced pluripotent stem cells

69
Q

What is an important structural protein in the stereocilia of hair cells?

A

Actin

70
Q

Other than tip links, what other links connect adjacent stereocilia?

A

Lateral links (in the middle of stereocilia) and ankle links (at the base of stereocilia)

71
Q

What are the 2 ends which connect to either end of a tip link called?

A

The upper tip link density and the lower tip link density

72
Q

Describe how tip links can be removed experimentally

A

If hair cells are treated with BAPTA (A calcium chelator) this destroys the tip links

73
Q

What happens to hair cell activity if tip links are removed with BAPTA?

A

Hair cells do not respond: tip links are required for hearing

74
Q

Can tip links be regenerated?

A

Yes, tip links can regenerate. Hair cells cannot

75
Q

Where are the mechanotransduction channels located on stereocilia?

A

At the lower tip link density

76
Q

How was it determined that mechanotransduction channels of stereocilia were located at the LTLD and not the ULTD?

A

In calcium imaging experiments, there was no cation influx at the tips of the tallest cilia, suggesting that channels must be at LTDL

If they were at UTLD, we would see activity at the top

77
Q

Describe the mechanical action exerted by tip links upon vibration of the basilar membrane

A

Tip link “tents” the shorter tip link, pulling on this and initiating a signaling cascade in the LTLD

78
Q

What is the proposed mechanosensory channel in the LTLD of hair cells?

A

TMC1/2 complex: complex of 4 proteins
TMC1/2 (main)
PCDH15-CD2
TMHS
TMIE

79
Q

Describe what is known about the mechanosensory channels in the stereocilia of the hair cells

A

TMC1/2 complex, associated with the LTLD and coupled to the mechanotransducer (MET) channel

80
Q

Do hair cells produce graded potentials or action potentials?

A

Graded potentials

81
Q

To depolarize a cell, which ions flow into the cell and why?

A

Ca and K+ go into the cell
This is because K+ is higher in the endolymph than it is in the cell

82
Q

Endolymph has (high/low) K+

A

High

83
Q

Perilymph has (high/low) K+

A

Low

84
Q

Describe which parts of the hair cells are exposed to endolymph and perilymph

A

Stereocilia: endolymph
Soma: perilymph

85
Q

Mechanotransduction channels of the stereocilia are closed when cilia are (direction)

A

Upright

86
Q

When stereocilia are pushed the “opposite direction” (force leading from tall side of staircase), the hair cell is…

A

Hyperpolarized

87
Q

Describe the intracellular pathway starting at deflection of stereocilia towards depolarization to recovery

A

Deflection > K+ and Ca++ influx > Opening of V-gated Ca++ channels > further Ca++ influx > Vesicle release > when K+ reaches soma (in perilymph, low K+) get K+ efflux > recovery

88
Q

Describe calcium-dependent fast adaptation

A

Ca++ influx helps depolarize the cell, but when inside the cell Ca++ acts on channels to close them to prevent further influx - this could involved dissociation from a gating spring, but this is just a theory

89
Q

Describe “slow” adaptation of hair cells

A

Calcium-dependent movement (via a myosin motor) of the upper tip link density down the stereocilium, which decreases tension on the tip link

90
Q

Describe how outer hair cells may be involved in cochlear amplification

A

Receive input and uses motor proteins such as prestin to make the soma of the cells grow or shrink, which could change the pressure of the stereocilia on the tectorial membrane - can amplify or quiet sounds to protect hair cells

91
Q

The auditory nerve is made of a collection of these neurons

A

Spiral ganglion cells

92
Q

What brain structures does afferent sound information pass through to get to the auditory cortex?

A

Cochlea > cochlear nucleus > superior olive > inferior colliculus > Medial geniculate nucleus (thalamus) > auditory cortex

93
Q

At which brain structure does sound information from both ears get combined?

A

Superior olive

94
Q

True or false: the superior olive maintains a tonotopic map

A

True

95
Q

At which brain centre is the tonotopic map of sounds lost?

A

None: maintained all the way to the auditory cortex

96
Q

Sounds associated with the apex of the cochlea are more (frontal/posterior) on the auditory cortex

A

Frontal

97
Q

What are the 3 vestibular organs of the inner ear called?

A

Utricle
Saccule
Ampullae (semicircular canals)

98
Q

What is the purpose of the vestibular system?

A

Information used to maintain body posture, eye position, and balance

99
Q

What are the sensory cells of the vestibular system?

A

Hair cells

100
Q

The semicircular canals are sensitive to this kind of movement

A

Head rotation (side to side and nodding movements)

101
Q

The otolith organs are sensitive to this kind of movement

A

Gravity and head tilts

102
Q

What is structurally different about hair cells of the vestibular system compared to the auditory system?

A

They maintain their kinocilia

103
Q

Describe how bending of stereocilia is initiated in the vestibular system

A

There is a gelatinous layer which covers hair cell stereocilia and when the head is moved the stereocilia are deflected

104
Q

What is otoconia in the otolith organ?

A

Bits of calcium carbonate which weigh down the gelatinous layer on top of the hair cells

Biology 404 (14 decks)

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