Auditory Circuits Flashcards
what does the outer ear contain
pinna and ear canal
filters incoming sound and sends to eardrum
what does the middle ear contain
ossicles (air-filled)
impedance matching
what does the inner ear contain
cochlear
semi-circular canals
vestibular apparatus
3 types of scalae (fluid-filled cavities)
vestibuli , media, tympani
vestibuli and tympani contains perilymph
vestibuli and supporting cells control homeostasis
where are the IHCs and OHCs located
organ of corti (also contains basilar membrane)
inside cochlea
role of OHC and IHC
OHC - active amplification
IHC - signal tranduction
role of stereocilia
located on the apical surface
signal transduction in the cochlea
undergo sheer force
deflected to longest stereocillia
steps in signal transduction
mechanoelectrical transducer channels (MET) open
causes hair cell depolarisation
influx of K+ ions in hair cells
driven by electrochemical gradient of scala media
Ca2+ channels depolairsation
vesicles fuse to hair cell membrane
NT release
IHC membrane potential
follows low stimulus frequencies
OHC membrane potential
follows very high stimulus frequencies
what does the OHC contain
prestin (in membrane)
alters conformation and length
what is the basilar membrane
where the sensory epithelium sits
where does frequency tuning occur
in the auditory nerve
projections from spinal ganglion to cochlean brainstem
where does the ascending auditory pathway project
brainstem
midbrain(inferior colliculus)
thalamic nuclei
cortex
what is the ascending auditory pathway response
contains crossed and uncrossed projections
response change is higher up in the CAS
cortex has a sluggish response
stimulus specific adaptations and dynamic change in response
binaural response
where does the descending auditory pathway project
cortex
thalamus
MB
BS
cochlea
what does the descending auditory pathway contain
complex crossed and uncrossed projections
corticofugal modulation (peripheral nuclei to cochlea) - alters hair cells and protects against excessive sound
olivocochlear feedback to OHC and protection against specific sound
monaural cues
pinna transforms sounds into spectral notches
perception of elevation above/below plane and resolution of front/back ambiguity
binaural cues
interaural time differences (ITDs)
interaural level differences (ILDs)
perception of azimuth (horizontal L/R plane)
mammalian vs avian
-birds and reptiles have widened interaural distance due to acoustic coupling of L/R middle ear cavities
-avian have larger ITDs (max=200us) than mammals with equivalent head size
ITDs
predominant binaural cue for low frequencies <2kHz
(wavelength > head diameter)
larger heads = more ITD detection
low frequencies diffract around the head
human ITD discrimination
small changes - 1-2 degrees of angular location
threshold = 10us
avian ITD
delay line arrangement - to give ITD sensitivity
map of auditory space in nuclear laminaris
EE cells in NL are coincidence detectors
temporal summation of EPSP inputs - excitation only
steps in ITD
1) sound reaches L ear first
2) AP towards MSO
3) sound reaches R ear
4) AP from R ear towards MSO
5) APs converge on MSO neuron which responds strongly if arrival coincident
mammalian ITD
ITD tuning in MSO not organised into space map
peak ITD function outside physiological range of ITDs
peak position cannot encode ITDs
maximum ITD occurs at midline
ILDs
predominant cue for high frequencies >2kHz
(wavelength<head diameter)
easily reflected by head
how are ITDs tuned
excitation
phase-locked inhibtion
lateral superior olive LSO
LSO neurons has glycingeric inhibtion and glutamatergic excitation
de novo degeneration of ILD sensitivity in IC and ILD in IC (crossed and uncrossed pathways)
