processing of natural sound
brain discriminates info from a mixed up sound and sepearted out in the cortex
auditory nerve (VIII)
carries neuronal information from IHC - connects to multiple spiral ganglion and sends to cochlear nucleus
ribbon synapses
hair cells rely on ribbon synapses
- depolarization caused by opening of MTC causes influx of Ca and release of vesicles
vesicles are organized around a ribbon
otoferlin gene
contains many genes for deafness
- see in IHC
- important in transmisison of signal from hair cells to spiral ganglion
- brainstem response is absent in knockout mice
what happens to Ca triggered exocytosis in otoferlin KO
exocytosis is abolished
- ability to cause increase in capacitance is gone and no vesicle release
- can increase capacitance by increasing SA or cage calcium
otoferlin and Ca
calcium sensory -
otoferlin is important in sensing calcium coming in- most neurons use synaptotagmin
pachanga mouse model
mutation in Otof leading to partiel loss of function
- normal hair cell transduction and receptor potentials but have severe hearing impariments
- transmission to spiral ganglion cell is warped
3 components of electrocochlearagraphy
measures stimulus related cochelar potentials
- cochlear microphonics : OHC
- summating potentials: IHC
- compound action potentials: Auditory Nerve
pachanga in vesicle release
- showed that you can still see vesicle release but to a lower extent, pachanga acts on relasable pool and doesnt allow to be recycled so cannot continue to release
- argued otof isnt Ca sensor but helps recycle vesicles
otoferlin as multifaceted Ca sensor
similar to snare - sensor of Ca
important in release- clears material from vesicular release site
temperature dependant deafness
patients have hearing loss with a fever
high frequencies an iHC
higher tones cant keep up and you see fusing
- brain doesnt need to follow stimulus to convey information
- basilar membrane of cochlea discriminates freq
phase locked response of ANF
for every cycle there is a burst of AP
3 divisions in cochlear nucleus
each ANF innervates all 3 CN divisions
- antereoventral CN (AVCN)
- postereoventral CN ( PVCN)
- dorsal CN (DCN)
- saw that there is cochleotopic organization of CN
what is the connection from auditory nerve to bushy cells
end bulb of Held
- bushy cells show improved precision of phase locking
- fidelity of firing is tronger downstream then it is upstream
cell types in VCN
spherical / globular bushy
stellate/multipolar
octopus cells
granule cells
discharge patterns in the CN
- much more complexity than auditory nerve fiber
- can respond both tonic and phasic to a tone
- discharge patterns shaped by time dependant interactions of excitation and inhibition
lateral inhibition - two tone suppression
tone elicits certain response
second tone in + area increases firing rate
second tone in - area decreases firing rate
auditory pathway
cochlear nucleus –> superior olive –> inferior colliculus–> MGN–> auditory cortex
organization in cortex
maintains tonotopic organization
- can see frequencies in diff locations
cortical cells
tuned to precise sequence of complex sounds
- ethologically important sounds
primary language areas of the brain
brocas: important for creating speech
lesion- understand language but cant produce speech
wernickes: how we understand speech
lesion- can speak but cannot understand
