The auditory system Flashcards

1
Q

What do we use sound for?

A

communication, emotion, recognising different sounds, 3D view of auditorial world, survival

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What features of sound need encoding?

A

frequency, intensity, onset, duration

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are the 3 chambers of the cochlear spiral from top to bottom?

A

scala vestibuli
scala media
scala tympani

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Where is the organ of corti and basilar membrane?

A

between the scala media and tympani

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What parts of the cochlear spiral contain perilymph?

A

scala vestibuli and scala tympani

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are the contents of perilymph?

A

low K+, normal Ca2+ and high Na+ (same as extracellualr fluid)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What are the contents of endolymph compared to perilymph?

A

high K+, low Ca+ and low Na+

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the purpose of the different ion concentrations in the cochlear chambers?

A

electrical driving force into hair cells is about 140mV overall which is vital for function

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is tonotopic organisation of the cochlea?

A

apex detects low frequencies and base detects high frequencies
sound wave travels from base to apex

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

How is the frequency of sound encoded?

A

the brain doesn’t receive sound- the position of the hair cell along the membrane that is depolairsed interprets how high or low it is
not coded by firing pattern, represented by location of cell only

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the characteristic frequency location?

A

the location on the basilar membrane where there is maximal movement for a certain frequency
lower sounds will be closer to the apex, higher will be closer to the base
determined by width and stiffness of basilar membrane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

High frequency sounds

A

short wavelength, low energy so don’t travel far and peak movement is at the base

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Low frequency sounds

A

long wavelength, high energy so travels further and peak movement is at the apex

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the role of inner hair cells?

A

primary sensory recpetors, encode all of the auditory info and pass it onto nerve fibres

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the role of outer hair cells?

A

not sensory receptors, act as cochlear amplifiers by shortening and lengthening in time with sound frequency- electromotility

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

How do inner hair cells initiate action potentials?

A

mechanosensitive ion channels that are called MET channels are at the tips of the shorter stereocilia
connected to tip links that pull the channels open when sound waves move the IHCs

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

At rest when no sound is present:

A

slight tension in tip links
resting inward MET current
K+ enters down large electrical gradient
main driving force pushing K+ into cells
conc gradient for K+ exit is bigger than entry
hair bundle in endolymph, depolarised

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

When there is excitatory stimulation:

A

large deflection of hair bundle toward taller stereocilia
increases tension in tip linkes and opens MET channels- high current
depolarises hair cells activating Ca2+ channels
increases activity in nerve fibres
activates K+ channels and K+ exits into perilymph to repolarise cell

19
Q

When there is inhibitory stimulation:

A

large deflection in hair bundle toward shorter stereocilia
tip links slacken and MET channels close
turns off MET current and hyperpolarises hair cell below resting potential
none-little neuronal activity
k+ channels open longer to fully repolarise cell

20
Q

How do hair cells react to sustained sound?

A

moves hair bundle back and forth at the sound frequency
creates cycle of membrane potential matching the frequency generating pulses of NT release

21
Q

Outer hair cell structure

A

do not have many afferents due to lack of sensory role
V shaped hair bundles with tip links and MET channels, VGICs and prestin in their cell membrane

22
Q

How do outer hair cells amplify stimuli?

A

shorten when depolarised
elongate when hyperpolarised
movement up and down amplifies movement of basilar membrane over narrow CF region
makes them sharply tuned and highly sensitive

23
Q

What happens if outer hair cells are damaged?

A

stimulation of IHC bundle is weaker so loss causes severe hearing loss but not complete deafness

24
Q

How is sound localised in the horizontal plane?

A

interaural level differences
interaural timing differences

25
Interaural level differences
the differences in loudness of the same sound at the two ears as little as 1 or 2 db head acts as a barrier that reflects or absorbs sound waves
26
Interaural timing differences
the difference in the arrival time of the same sound at the two ears as small as 10um sounds are delayed in the far ear compared to the near one
27
Sound localisation centres
through the cochlear nucleus to the lateral superior olive, medial superior olive and medial nucleus of trapezoid body one of each either side of the midline so theres always a near and far one
28
What are the main centres involved in ILD and ILT detection?
lateral superior olive medial superior olive
29
How are inputs from the two LSOs integrated?
each LSO receives + from near ear and - from far ear outputs of LSOs are opposite but balanced, where excitatory input is the highest is where sound is loudest combined input gives accurate indication of position of sound
30
How is sound in a central position received?
the more central the sound is the more the two LSOs overlap so accuracy is very high so small changes in the centre are detected rapidly which is vital for hunting
31
How are ILDs encoded by the two LSOs?
two LSOs act as two channels broadly tuned to sounds mainly from the same side of the head made up of many neurons tuned to different ILDs position recognised by balanced and opposite inputs from LSOs
32
Tiny differences in a sounds arrival time are detected by what centre?
MSO by the principle neurons
33
When is the MSO maximally active?
when both inputs arrive simultaneously
34
How does the MSO detect differences in the timing of sounds?
excitatory inputs from both ears converge on neurons in MSO neurons are different lengths which is key to function activity from far ear takes longer to reach MSO than the input from the near ear mirror image of MSO on other side of head neurons compare coincident arrival of excitatory inputs
35
How are the initial circuits for sound localisation calibrated?
using alignment with the visual map- hardwired auditory map is aligned to overlay the visual map based on geneticd and formed early on, doesn't depend on sensory function
36
What is the function of the medial nucleus of the trapezoid body in ILD?
turns input from the far ear into an inhibitory signal
37
What nuclei are involved in the integration of visual and auditory information?
central nucleus of inferior colliculus external nucleus of inferior colliculus optic tectum
38
Central nucleus of inferior colliculus
neurons tuned to specific ITDs organised in frequency specific layers show little adaptive plasticity
39
External nucleus of inferior colliculus
projections from ICC layers converge on neurons of ICX forms map of auditory space site of large scale adaptive plasticity
40
Optic tectum
combines auditory map from ICX with visual map overlapping receptive fields feedback projections to ICX site of large adaptive plasticity
41
What is the difference between the auditory and visual maps?
visual map adjusts rapidly but auditory takes longer visual map may be dominant for space perception over auditory
42
What part of the brainstem is involved in ITD detection?
medial superior olive
43
What parts of the brainstem is involved in ILD detection?
lateral superior olive medial nucleus of trapezoid body