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Neural Circuits > L6 - Auditory System > Flashcards

L6 - Auditory System Flashcards

1
Q

What pressures did animals face as they moved out of water?

A

Evolutionary pressure to detect sounds travelling in air

Appearance of tympanic ear

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2
Q

The important of sensing sound developed in?

A

Early mammals - small and nocturnal

Evolved massive range of frequency and intensity sensitivity

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3
Q

How is sound faithfully relayed from HCs to the brain?

A

Highly specialised structures and mechanisms in cochlea

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4
Q

What do we use sound for?

A 
Communication
Topographic view of auditory world
Survival
Emotion 
Navigation
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5
Q

What 4 features of sound need encoding?

A

Frequency
Intensity
Latency
Duration

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6
Q

Sound frequency

A

Pitch is measured in Hz
A wide range of sound frequency has to be covered (x103)
Achieved by cochlear mechanics and physiology of hair cells
Mainly encoded by the BM region stimulated

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7
Q

Sound intensity

A

Loudness is measured in dB
A huge range of sound intensity has to be encoded (x1012)
Achieved by the firing rate of many ANFs

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8
Q

Sound latency

A

A rapid onset is important for localising different sounds and creating a topographic map

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9
Q

Sound duration

A

Ear has to remain sensitive to sounds for long periods without fatigue
The sensory cell synapses are specialised for sustained neurotransmission

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10
Q

Method of sound travel through the cochlea

A
  1. Sounds enter ear canal
  2. Causes vibration on the tympanic membrane
  3. Causes vibration of malleus, incus and stapes
    - Lever action of the bones amplifies the movement and pushes fluid in the cochlea
  4. Transmits vibrations of tympanic membrane to the round window
  5. Causes vibration of fluid inside the cochlea
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11
Q

Overview of the scala media

A

Middle layer
Contains organ of corti and sensory cells
Separated from tympani by basilar membrane
Separated from vestibula by Reissners membrane
Specialised cells in the stria vascularis

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12
Q

What lymph does the scala media contain?

A

Endolymph
Normal intracellular fluid
- High K – 150 mM
- Brought about by cells in the stria vascularis
- Generates the endocochlear potential - +80mV
- Low Ca – 20 uM

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13
Q

What lymph does the scala vestibula contain?

A 
Top layer 
Perilymph 
Normal extracellular fluid 
- Low K – 5mM
- Normal Ca – 1.3mM
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14
Q

What lymph does the scala tympani contain?

A 
Bottom layer
Perilymph 
Normal extracellular fluid 
- Low K – 5mM
- Normal Ca – 1.3mM
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15
Q

What does the cochlear VIIII nerve innervate?

A

Innervates the organ of corti

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16
Q

What are spiral ganglions?

A

Found within the cochlea

Where cell bodies of all the neurons are found

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17
Q

What are the two types of sensory cells within the organ of corti?

A 
1 row of inner hair cells 
- 4,000
- Main sensory cells 
- Once damaged cannot be replaced 
3 rows of outer hair cells 
- 12,000
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18
Q

What are some supporter cells within the organ of corti?

A

Deiter cells - below OHC

Pillar cells – between IHC and OHC

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19
Q

What are the two types of neurones within the organ of corti?

A

Type 1 spinal ganglion neurons – innervate IHC
- Carry sound info from IHC to brain
Type 2 spinal ganglion neurons – innervate OHC

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20
Q

What are the two types of efferents within the organ of corti?

A

Allows some control of the sounds we concentrate on

  • Lateral effects – synapse with IHC
  • Medial efferents – synapse with OHC
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21
Q

How is the mammalian cochlea organised?

A

Tonotopically
Cells at base – respond to high frequency sound
Cells at top – respond to low frequency sounds
Relay sounds to the cochlea nucleus in the brainstem

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22
Q

Human hearing frequency range

A

20Hz – 20kHz

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23
Q

Bat hearing frequency range

A

2kHz-120kHz

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24
Q

Mice hearing frequency range

A

900Hz – 79kHz

25
Whale hearing frequency range
14Hz – 36Hz | Low frequency sounds travel better in water
26
How is tonotopicity established?
By the basilar membrane travelling wave
27
Establishing tonotopicity method
1. Sound enters ear and initiates a wave along the basilar membrane, which is tuned to sound frequency 2. Vibration of tympanic membrane 3. Lever action causes pressure wave in fluid in cochlea 4. Pressure wave travels along cochlea and causes maximum stimulation of particular region on basilar membrane - Reaches a peak at its best frequency - Depends on stiffness of basilar membrane
28
Low frequency sounds cause maximum deflection of?
Travel further | Cause maximum deflection at apex of basilar membrane
29
High frequency sounds cause maximum deflection of?
Cause maximum deflection at base of basilar membrane | Where its stiff and short
30
Tonotopicity is preserved throughout the auditory pathway from?
1. Cochlea where it established 2. Auditory centres in brainstem 3. Midbrain 4. Auditory cortex 5. Cerebral cortex
31
General hair cell 5 key features
``` Hair bundle Stereocilia Transducer channels K channels Ca channels ```
32
Hair bundle facts
On top | Stimulated by movement of fluid in cochlea
33
Transducer channel facts
On top of stereocilia Mechanically gated Attached to next to stereocilia via a tip link Force in this tip-link opens the channels
34
What is the role of K channels on the membranes of hair cells?
Outward movement of K to polarise cell
35
What is the role of Ca channels on the membranes of hair cells?
Inwards movement of Ca to stimulate exocytosis of vesicle releasing neurotransmitter
36
General hair cell at rest method
1. Resting tension on tip links that opens some of transducer channels 2. Allows some K ions to enter cell 3. Depolarises cell to resting potential = -55mV 4. This depolarisation activates some Ca channels producing resting activity in efferent fibre
37
General hair cell excitation method
1. Push hair bundle towards taller stereocilia 2. Increases tension in tip-links 3. Opens all channels in the hair bundle 4. Maximum transducer current - Can be measured with a patch clamp 5. Depolarises hair cells to -30 mV 6. Opens Ca channels in cell 7. Lots of neurotransmitter released 8. Increased firing frequency of efferent fibre
38
General hair cell inhibition method
1. Sound stimulation pulls hair bundle back in inhibitory direction – away from taller stereocilia 2. Closes all transducer channels in stereocilia 3. Outflow of K through K channels 4. Hyperpolarisation of cell to -65 mV 5. Decreased firing frequency of efferent fibre
39
Inner hair cells - hair bundle
Tall row and two small rows of stereocilia | Ions channels on small rows
40
Inner hair cells - synaptic ribbons
Electron dense bodies in synapse region Act as a store for synaptic vesicles High rates of exocytosis for long periods of time
41
Inner hair cells - K channels
3 types - Fast activating - Slow activating - Low voltage
42
In response to sound inner hair cells?
Flicks between excitatory and inhibitory states, firing action potential in efferent fibre
43
Inner hair cells - low and high frequency cells
Low frequency and high frequency cells respond to sound in different ways
44
Outer hair cells - hair bundles
More W shaped than IHC bundles
45
Outer hair cells - role
No role in transmitting sensory info | Involved in cochlea amplification
46
Outer hair cells - innervation
``` Innervated heavily be efferent fibres - Release Ach which is linked to K channels - Inhibitory effect of cell Small amount of afferent fibre input - Not as much as IHCs ```
47
What protein do outer hair cells have in their membrane?
Prestin Motor protein that in response to Cl movement enables cell to contract or elongate - Conformational change Means OHCs Can respond faster than IHCs
48
Outer hair cell - at rest
More depolarised than IHCs = -40mV | Allows cells to respond faster
49
Outer hair cell - in response to sound
Cell contracts and elongates rapidly - Contraction – excitatory - Elongation – inhibitory
50
What is the importance of outer hair cells being attached to the tectorial membrane?
The OHC receptor potential activates somatic motility that enhances the mechanical stimulation of IHCs
51
Neurons in the cochlea - Type 1 afferents
Innervate IHCs 95% of fibres Carry sound information to the brain Innervated by up to 30 type 1 afferent fibres Each fibre has a limited rate at which it can fire action potentials - Many fibres allows summation Have both low threshold and high threshold fibres - Low – quieter sounds - High – louder sounds
52
Neurons in the cochlea - Type 2 afferents
Innervate OHCs 5% of fibres Involved in nociception Enters organ of corti and bends towards basal side 1 fibre innervated 10-30 OHCs Only respond when all OHCs they innervate are activated
53
Neurons in the cochlea - lateral efferent fibres
Innervate IHCs – type 1 | Allow dynamic control of cochlear output
54
Neurons in the cochlea - medial efferent fibres
Innervate OHCs – type 2 | Allow dynamic control of cochlear output
55
Auditory pathway - cochlear nucleus
All afferent fibres from the cochlea Two main pathways: - Red from ventral CN – sound localization - Green from dorsal CN – sound recognition
56
Auditory pathway - superior olivary complex
Sound localisation
57
Auditory pathway - inferior and superior colliculus
Integration with non-auditory inputs | E.g. somatosensory and vision
58
Auditory pathway - medial geniculate nucleus
Involved in learning and memory
59
Auditory pathway - auditory cortex
Involved in cognition, attention, memory, decision making

Neural Circuits (15 decks)

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