which membrane separates the scala media from the scala vestibuli?
reisner’s membrane
which membrane separates the scala media from the scala tympani?
basilar membrane
what does the scala media contain?
endolymph = high k+ low ca2+
what is the stria vascularis
actively transports K+ into scala media
deiter’s cells
supporting cells below OHCs
pillar cells
supporting cells in between IHCs and OHCs
type I afferents
carry information from IHCs to brain
type II afferents
carry information from OHCs to brain
involved in nociception
lateral efferents
synapse onto type I fibres
switches off type I fibres to protect from overactivity
medial efferents
synapse directly onto OHCs
inhibitory
tonotopic organisation of cochlea
cells at base of cochlea respond to high frequency sounds
cells at apex of cochlea respond to low frequency sounds
hair cells send information to the cochlea nucleus in the brain. same tonotopic organisation is preserved
what is the human hearing range?
20Hz - 200Khz
describe what happens when the hair cell is at rest
- resting tension opens some transducer channels
- some k+ enters cell and depolarises membrane slightly = -55mV
- depolarisation activates some Ca2+ channels
- resting activity in afferent fibre produced
describe what happens when the hair cell is excited
- hair cell is stimulated + hair bundle pushed towards tallest stereocilia
- increased tension in tiplinks opens all channels in hair bundle
- hair cell is depolarised which opens majority of Ca2+ channels
- a lot of neurotransmitter released onto afferent fibres
- increased firing rate of afferent fibre
describe what happens when the hair cell is inhibited
- hair cell is stimulated so hair bundle pulled away from tallest stereocilia
- decreased tension in tip links closes all transducer channels
- outward flow of k+ through k+ channels hyperpolarises cell
- no ca2+ channels open
- reduced firing rate of afferent fibre
where are the ion channels located on the stereocilia
shorter rows of stereocilia
what is a synaptic ribbon?
specialised electron dense bodies in synaptic region of hair cell
store of synaptic vesicles to maintain high rates of exocytosis for a long time
what is the role of OHCs?
cochlear amplification
Prestin
motor protein in OHC membrane allowing OHC to contract or elongate in response to Cl- movement
how are type II afferents involved in nociception
active when all OHCs they innervate are active –> produces dangerously loud sound
signals to brain to turn cells off via efferent fibres
which marker is present in both hair cells?
myosin 7a
which marker is expressed in IHCs?
otoferlin
which marker is expressed in all fibres in cochlea?
βIII-tubulin
what is the pathway from the ventral cochlear nucleus important for?
sound localisation
