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BMS 248 - Neural circuits > Overview of the auditory system > Flashcards

Overview of the auditory system Flashcards

1
Q

Describe the development of sensing sound over evoultion

A
  • First amphibians had some sensory cells - sense the movement of water around the body
  • As move out of water onto land - evolutionary pressure to sense sounds carried by the air
  • Evolved massive range of frequency and intensity sensitivity
  • Lead to the formation of the tympanic ear
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2
Q

What is important about the evolution of the tympanic ear?

A

Appeared 3 times over evolution, in:

  • Mammals
  • Amphibians
  • Birds

Shows that this structure is very important

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3
Q

What is sound frequency?

What is it measured in?

A
  • Amount of waves per second
  • The pitch of sound

Measured in Hz

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4
Q

How are wide ranges of sound frequency detected?

A

By the cochlear mechanics and physiology of the hair cells

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5
Q

What is sound intensity?

What is it measured in?

A

The volume of the sound

Measures in dB

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6
Q

How are wide ranges of sound intensity detected?

A

By the firing rate of many afferent nerve fibres that innervate the hair cells of the cochlea

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7
Q

What is a rapid onset of sound important for?

A

Localising different sounds
and
Creating a topographic map of the auditory sound in the brain

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8
Q

How are the sensory cell synapses of the auditory system different to conventional synapses?

Why?

A

They are specialised for sustained neurotransmitter release

So that the ear remains sensitive to sounds constantly

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9
Q

Describe the pathway for sound from the outer ear to the cochlear

A
  • Auricle funnels the sounds into the ear canal
  • Vibrates the tympanic membrane
  • Vibrates the ossicles, which transmit the vibration of the tympanic membrane to the round window
  • Causing a vibration of fluid in the cochlear
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10
Q

What is the auricle of the ear?

What does it do?

A

The external, visible part of the ear

Shapes the sounds and funnels them into the ear canal

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11
Q

What is another name for the tympanic membrane?

A

The ear drum

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12
Q

What are the ossicles of the ear?

Why are they necessary?

A

Malleus, Incus and Stapes

  • Transmit the sound induced vibration of the tympanic membrane to the fluid movement in the cochlear
  • To AMPLIFY the movement of air
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13
Q

What would happen if the ossicles were not present

A

Air would bounce off the round window

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14
Q

What is contained in the middle ear?

A

Tympanic membrane

Ossicles

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15
Q

What is contained in the inner ear?

A

Cochlear

Vestibular organs

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16
Q

What are vestibular organs important in?

A

Balance

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17
Q

What are the vestibular organs?

A
  • Semi-circular canals

- Utricle and saccule

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18
Q

What are the chambers of the cochlear? (base to apex)

A

Scala Tympani
Scala Media
Scale Vestibuli

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19
Q

What is the scala media also called?

A

The cochlear duct

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20
Q

What is the cochlear innervated by?

Where does it enter the cochlear?

What does it innervate?

A

The cochlear nerve (VIII)

Enters the cochlear through the core (modiolus)

Innervates the organ of corti

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21
Q

Where are the cell bodies of the neurons in the ear?

A

In the spiral ganglion

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22
Q

Where are the sensory cells are the ear?

A

In the organ of corti

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23
Q

Which chamber/s of the ear contain endolymph?

A

Scala media

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24
Q

Which chamber/s of the ear contain perilymph?

A

Scala tympani

Scala vestibuli

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25
Q

Describe endolymph

A

Like intracellular solution:

  • High K
  • Low Ca2+
  • Positively charged (80mV)
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26
Q

Describe perilymph

A

Like extracellular solution:

  • Low K+
  • Normal levels of Ca2+
  • 0mV
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27
Q

What causes the high levels of K+ in the scala media/endolymph?

What does this produce?

A

Stria vascularis - actively transports K+ into the scala media

Produces an endocohclear potential of +80mV

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28
Q

What is around the outside of the scala media?

A

Stria vascularis

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29
Q

What separates the scala tympani from the scala media?

A

Basilar membrane

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30
Q

What separtates the scala media from the scala vestibuli?

A

Reissner’s membrane

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31
Q

In which chamber of the cochlear is the organ of corti present?

A

In the scala media

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32
Q

What does the organ of corti constist of?

A
  • Tectorial membrane
  • 1 row of IHCs
  • 3 rows of OHCs
  • Supporting cells
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33
Q

What happens to the hair cells in the ear once they are damaged?

A

They cannot be replaced

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34
Q

How many IHCs are there?

How many hair cells in total?

A

4,000 IHCs

16,000 total hair cells

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35
Q

What are the support cells in the organ of corti and where are they present?

A
  • Deiter cells (underneath the OHCs)

- Papillar cells (between the OHCs and the IHCs)

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36
Q

What do the type I spiral ganglion neurons do?

How is this different tot he type II SGNs?

A

Innervate IHCs

Type II innervate the OHCs

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37
Q

What is the function of type I SGNs?

A

Carry sound information from the IHCs to the brain

38
Q

What is the function of type II SGNs?

A

Believe they are involved in nociception (dangerously loud stimulation)

39
Q

What is the function of efferent feedback from the brain to the organ of corti?

A

Allow control over the sound we concentrate on

Prevents the cells from becoming over stimulated

40
Q

What do lateral efferents synapse with?

A

Type I SGNs

41
Q

What do medial efferents synapse with?

A

Directly with OHCs

42
Q

Which cells in cochlea respond to high frequency?

Low frequency?

A

Base - high frequency

Apex - low frequency

43
Q

Where is the base of the cochlea?

Apex?

A

Base - near the ossicles

Apex - point of the cochlear (middle of the spiral)

44
Q

Where does the cochlear relay sound information to?

A

The cochlear nucleus in the BRAIN STEM

45
Q

What is the organisation of the cochlear reflected in?

A

The organisation in the cochlear nucleus and further along in the auditory pathway

46
Q

What is the hearing range of humans?

A

20Hz - 20kHz

47
Q

Which animals have high frequency hearing?

Low frequencies?

A

High frequencies:

  • Bats
  • Dolphins
  • Mice

Low frequencies:
- Whales

48
Q

Why is an advantage of mice to have high frequency communication?

A

Birds (predators) hear low frequencies

49
Q

What does the pressure wave in the cochlear cause?

What is this determined by?

A

Maximum deflection of the basilar membrane, depending on stiff the membrane is - dependant on how far the wave travels

How far the wave travels is determined by the FREQUENCY of the sound

50
Q

What is the structure of the basilar membrane at the base?

What causes maximum deflection here?

A

Stiff and narrow

Maximum deflection by HIGH frequency sounds

51
Q

What is the structure of the basilar membrane at the apex?

What causes maximum deflection here?

A

Wide

Maximum deflection by LOW frequency sounds

52
Q

What does deflection of the basilar membrane by the pressure wave cause?

A

Stimulation of the hair cells in that region of the cochlear

53
Q

What is tonotopicity?

How is it established and preserved in the auditory pathway?

A

The spatial arrangement of where sounds of different frequency are processed in the brain

Established in the cochlear by the traveling pressure wave

Persevered ALL the way along the auditory pathway (brainstem, midbrain, auditory cortex, cerebral cortex) - Kept seperate

54
Q

What are the 4 major components of the hair cell?

A

1) Hair bundle
2) Stereocilia
3) K+ current
4) Voltage gated Ca2+ channels

55
Q

What channels do the sterocilia have?

How are these channels opened?

A

Mechanically gated K+ channels

Channels opened by generating force in the tip links

56
Q

How are sterocillia linked to each other?

A

Through tip links

57
Q

What occurs in the hair cells at REST?

A
  • Resting tension on the tip links
  • SOME K+ channels open
  • SOME Ca2+ channels are activated
  • RESTING activity in the afferent fibre
58
Q

What occurs to the hairs cells when ACTIVATED by sound?

A

Hair bundle moves backwards and forwards, causing PULES of transmitter release and activity in the afferent fibre

59
Q

What happens when the hair cells are pushed in the direction of the TALLEST stereocillia?

A

Excitation:

  • Increase tension in tip links
  • K+ channels open
  • Maximum inward current
  • Depolarises the hair cell to -30mV
  • Opens majority of Ca2+ channels
  • More neurotransmitter released - increasing the firing of the afferent fibre
60
Q

What is the resting potential of the hair cell?

A

-60mV

61
Q

What happens when the hair cells are pushed in the direction of the SMALLEST stereocillia?

A

Inhibition:

  • Slack on the tip links
  • Closes K+ channels AND the small resting current
  • Hyperpolarisation - outward movement of K+ through a different channel (not transducer channel)
  • Potential to -65mV
  • Ca2+ channels closed
  • Reduced firing of action potentials
62
Q

Describe the sterocilia in IHCs

A

Tall sterocilia and 2 shorter rows

63
Q

Where are the ion channels in the sterocilia present?

A

In the shorter rows

64
Q

What are synaptic ribbons of the IHCs?

A

Specialised electron dense bodies in the synaptic region of IHCs that STORE synaptic vesicles

65
Q

What is the function of synaptic ribbons?

A

Store synaptic vesicles to maintain high levels of EXOCYTOSIS over long periods of time

66
Q

Where are synaptic ribbons not found?

A

In CONVENTIONAL synapses

67
Q

What channels are present in IHCs?

A

Transducer channel

3 types of K+ channel

  • Fast acting
  • Slow acting
  • Active at -ve voltages
68
Q

How do high frequency and low frequency IHCs respond to sound?

A

In DIFFERENT ways

69
Q

What can the cell membrane of the IHC do?

A

Filter out the phasic component (when the hair cells move backwards and forwards, leading to activation and inhibition)

And respond with a SUSTAINED POTENTIAL for the duration of the stimulus

70
Q

What do OHCs involved in?

How?

A

Cochlear amplification

When they contract - causes IHCs to contract more

71
Q

How are the hair bundles of the OHCs arranged?

A

In a V shape

72
Q

What are OHCs innervated by?

What can these neurons do?

A

Medial efferent fibres from the brain

These neurons can release Ach, to activate Ach receptors that are linked to the K+ channels of the OHCs
- Inhibiting the OHC

73
Q

What is prestin? What does it allow?

Wheres is it present?

A

Motor protein that enables the cell to contract or elongate in response to Cl- movement

Present in the cell membrane of the OHCs

74
Q

What happens prestin in the OHCs when they are depolarised?

What does this cause?

A

Conformational change in prestin

Shortening the length of the OHC

75
Q

What happens prestin in the OHCs when they are hyperpolarised?

What does this cause?

A

Conformational change

OHC elongates

76
Q

What is the resting potential of OHCs?

Why?

A

-40mV (higher than IHCs)

Allows the OHCs to respond faster than the IHCs

77
Q

Which hair cells are attached to the tectorial membrane?

A

OHCs

78
Q

How many type I afferent fibres innervate IHCs?

Why is this needed?

A

MANY (10-15)

Allows SUMMATION to occur

79
Q

How do the IHCs respond to volume of sound?

A

Each afferent type I fibre that innervate one IHC has a different threshold for sound

80
Q

When do type II afferent neurons respond?

A

When all OHCs that they innervate are active

81
Q

How do the efferent fibres from the MEDIAL centres of the brain act?

A
  • INHIBITORY affect on the OHCs

- Turn off the action of the amplifier when active

82
Q

How do the efferent fibres from the LATERAL centres of the brain act?

A
  • INHIBITORY

- Protect the afferent fibres by switching them off to prevent overactivity

83
Q

What are the stages of the auditory pathway?

A

1) Cochlear nucleus
2) Superior olivary complex (SOC)
3) Inferior (IC) and superior colliculus (SC)
4) Medial geniculate nucleus (MGN)
5) Auditory cortex (AC)

84
Q

Where are the cochlear nucleus and SOC?

A

In the brain stem

85
Q

Where do ALL fibres from the cochlear go to?

A

The cochlear nucleus

86
Q

What are the branched from the cochlear nucleus?

What are these branches involved with?

A

DCN (dorsal) - sound RECOGNITION

VCN (ventral) - sound LOCALISATION

87
Q

What is the SOC important for?

A

Sound LOCALISATION

88
Q

What is the binaural first site of auditory pathway?

A

Superior olivary complex

89
Q

What happens in the inferior and superior colliculus?

A

Integration of auditory and non-auditory inputs

ALL sensory information

90
Q

What is the medial geniculate nucleus involved in?

A

Learning and memory

91
Q

What is the auditory cortex involved in?

A

Cognition, attention, memory, decision making

BMS 248 - Neural circuits (16 decks)

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