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Neural extras > Lecture 6 Auditory system > Flashcards

Lecture 6 Auditory system Flashcards

1
Q

Evolution importance of sound

A
  • Early mammals small and nocturnal.
  • Evolved massive range of frequency and intensity sensitivity
    ALSO evolved independently 3 times
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2
Q

Range of sound intensity that needs to be encoded

A

x10^12

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3
Q

Perilymph concentration of K+/Ca2+

A

K+ 5mM

Ca2+ 1.3mM

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4
Q

Endolymph concentration of K+/Ca2+

A

K+ 150mM

Ca2+ 20 micromolar

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5
Q

Stria vascularis

A

Create unusual composition of ICF as actively pump K+ into SM creating endocochlear potential

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6
Q

Tonotopic organisation - describe shape of cochlea

A

Spiral

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7
Q

Tonotopic organisation - describe base/apex

A

Base HC = hi freq
Apex = lo freq
preserved in org of nerve fibres and along auditory pathway

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8
Q

Where is tonotopicity preserved

A 
cochlear
BS
Midbrain 
Thalamus 
Cortex
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9
Q

Describe reverse piano

A

SHC in cochlea organised like keys on piano
Each IHC = individual key
Reverse as sound of 1 freq activates key detected by body

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10
Q

Pitch apical vs base

A

Base = high pitch

vice versa

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11
Q

How much stiffer is base of basilar membrane

A

100x

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12
Q

Describe general hair cell

A

Stereocilia on apical surface
Mechanoelectrical transducer channels with tip links
VG K+ channels - basolateral - recycle K+ to repolarise, also cause depolarisation
VG Ca2+ channels for Ca2+ influx for release of NT
Nerve fibres

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13
Q

AT REST GHC

A 
VM = -55mV
slight tension on tip links 
rest MET current
large elect grad K+ entry 
depolarises rest Vm
resting (tonic activity) of nerve fibres due to slight dep meaning Ca2+ in
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14
Q

Excitatory deflection

A 
Large deflection hair bundle 
Max tip link tension 
Large MET current
Fully dep HC
-30mV
rapid train of AP
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15
Q

Describe repolarisation after excitatory deflection

A

VG K+ channels move K+ out to repolarise HC to rest Vm

Low K+ in perilymph vs HC means rapid

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16
Q

Inhibitory deflection

A 
Large deflection opp direction 
Min tip link tension 
No MET current 
Fully hyperpolarise HC below rest Vm 
-65mV
  No or very few action potentials
17
Q

Explain hyperpolarisation by K+ channels

A

Unusual K+ channels dep and hyper

Because K+ channels open longer vs Ca2+

18
Q

IHC function and follows…

A

Primary sensory receptor of cochlea

same sequence as GHC

19
Q

IHC K+ channels

A

Vary in activation ranges, size current, kinetics

fast, slow, negative

20
Q

Explain change in Vm inside IHC

A

Vm oscillates as between dep/hyper at same frequency as stimulus
low freq = AP pulse matches sound frequency
high freq = sustained AP train

21
Q

Describe OHC

A

V shape hair bundle
Majority of nerve contacts are efferent fibres
Prestin in cell membrane required for electromotility

22
Q

explain efferent OHC fibres

A

inhibitory and assoc with postsynaptic cisterns

23
Q

Transduction of OHC

A

rest = -40mV

with sound get dep/hyper matching sound freq

24
Q

Shortening of OHC

A 
BM moves up 
tip links tighten 
OHC dep
motor proteins contract
OHC contract
shorter
amplifies movement of BM
25
Q

Importance of cochlea amplification

A

causes sharp increae in BM displacement over narrow region

so each IHC tuned to narrow frequency band

26
Q

Type I afferent carry

A

all sound into from IHC to cochlea nucleus

27
Q

Type II turn

A

basally to innervate higher freq

28
Q

Type II structure

A

branched to conact up to 30 OHC + synapse onto cochlear nucleus

29
Q

Type II function

A
  • Thought to be related to nociception in the cochlea caused by damage/overstimulation.
30
Q

Movement of the BM displaces

A

the hair bundles of HCs in the organ of Corti, opening MET channels that depolarise the cells.

31
Q

The OHC RP activates and enhances

A

activates electromotility that enhances the mechanical stimulation of IHCs and improves tuning in the cochlea.

Neural extras (7 decks)

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