phys of auditory system Flashcards
how is the basilar membrane structured?
varied over its length
narrow and stiff near oval and round windows
wider and more flexible near helicotrema
how do high frequency sounds affect basilar membrane?
greater deflection where it is narrow
how do low frequency sounds affect basilar membrane?
greater deflection where it is loose and flexible
where is frequncy of sound decoded?
where there is greatest deflection along membrane
amplitude of sound?
sound pressure specifiied by a level
sound?
oscillations of air pressure that vary alot
frequency?
number of oscillations of pressure per second
how do sound waves propogates through basilar membrane?
initiated at basilar membrane, same frequency as sound
goes from base to apex
reaches point of maximal displacement of basilar membrane
what determines how far sound wave propogates through basilar membrane?
the flexibility of the membrane
higher frequency sounds max out at base
low frequenc max out at apex
result in tonotopy
what causes stereocilia of outer hair cells to be displaced?
pressure differential by vibration of basilar membrane
results in shearing force against stationary tectorial membrane
stereocilia displaced in that plane
how are inner hair cells activated?
fluid movement through cochlear duct
how does depolarzation of cell occur?
cation channels open at apex of stereocilia
connected to each other via tip links
transmit force to elastic gating spring, opens TRPA1 channels
what kind of channels are TRPA1? whats so special about them?
mechanotransduction, immediate effects
can respond to stimulus within 50us
dont need receptor potentials
small vibrations such as .3nm can open channel
where is endolymph made and whats its composition?
where is it
stria vascularis, but located in membranous labyrinth
bathes apical side of hair cells, in scala media
high in K, similar to ICF
where is perilymph made and whats its composition?
where is it
bathes basal end of hair cells
High Na, like ECF
scala vestibuli and tympani
what happens when cation channel open ?
bathed in endolumph
causes influx of K, which causes hair cell depolarization
what happens after hair cell is depolarized?
Ca channels at base of cells open
NT vesicules fuse to basilar membrane, release glutamate into cleft
afferent nerve fibers are stimulated, transmit signal to CNS
upward displacemtn of basilar membrane causes what?
shearing force that results in lateral displacement of stereocilia
eventually, depolarization of hair cell
where is hair cells located?
tips of stereocilia are in tectorial membrane
bodies are on basilar membrane
downward displacemtn of basilar membrane causes what?
hyperpolarization of hair cell
what hair cells are responsible for hearing?
inner hair cells, most cochlear nerve fibers come from here
outer hair cells amplify signals that are read by inner hair cells
what maintains electrochemical properties of endolymph?
stria vascularis
howis intraepithelial plexus formed? how does it allow endolymph to have high ?
cells of stria vascularis extend processes and folds around capillaries
K released from capillaries flows into endolymph
what forms BLB and how is it relevant?
endocochlear potential which drives positively charged ions into hair cells
maintained bystria vascularis
one of the main sites of drug entry to access inner hair cell
how do ototoxic cells disrupt hearing?
disrupt function of stria vascularis, diminsh endocochlear potential
What are inner hair cells, how are they organized, what do they do?
primary source of auditory info
arranged in a single layer
synapse with peripheral terminal of primary afferent sensory neuron
modulated by efferent neuron as well
What are outer hair cells, how are they organized, what do they do?
amplify sound waves, moving basilar membrane
specialied type of epithelial cell
contractile, boost vibration of membrane , amplify
three rows
synapse with sensory afferent from spiral ganglion and terminals from efferent neurons
what are otoacoustic emissions?
retrograde movement through oval window and through ossicles to cause tympanic memebrane to move
what are otoacoustic emissions used to measure?
function of inner and middle ears in infants
how do otoacoustic emissions travel?
from superior olivary complex
“olicocochlear efferents”
what does medial olivary complex innervate?
outer hair cells
what does lateral olivary complex innervate?
inner hair cells
what is OAE used to screen for?
presence of absence of sound waves generated by cochlear outer hair cells
used to screen for sensorineural hearing loss but not auditory neuropathy
how does olivocochlear efferents protect cochlea from extreme sounds?
reduce motility of outer hair cells
decrease motion of basilar membreane
reduce responses of inner hair cells and auditory nerve fibers
how do middle ear efferents protect cochlea from extreme sounds?
tensor tympani atenuates sound
stapedius attenuates sound
bilateral response to high sound
contraction decrease transmission of sound
act at low frequencies, prevent low frequency masking
may prevent damage, protect hair cells
what is implicated in tinnitus?
middle ear efferents
how do autonomic efferents protect cochlea from extreme sounds?
arises from 8th CN
sympathetic adrenergic
regulates vascular tone in clood supply from cochlea
what mechanisms protect cochlea from damage?
olivocochlear efferents
middle ear efferents
autonomic efferents
what does dorsal cochlear nuclei do?
integrates acoustic info with somatosensory info
what does ventral cochlear nuclei do?
processes temporal and spectral features of sound
what kind of input do olivary complexes receive?
glutamatergic input
MSO does what?
interaural time differences to help localize sound
LSO does what?
map of interaural intensity differences to help localize sound
what does inferior colliculus do?
suppresses echoes, helps with localization
time and intensit differences converge to help find precise origin of sound along horizon
what does medial geniculate nucleus do?
convergence from spectral and temporal pathways,
process speech inflections
precise info regarding intensity, frequency, binaural properties of sound relayed forward
what does primary auditory cortex do?
conscious perception of sound
higher order processing of sound (loudness, volume changes, frequency changes)
what does secondary auditory association cortex do?
brocas, wernickes, etc
tonotopic map not maintained, unlike others
complex sounds, sound , speech
where does sensorineural hearing loss come from?
problems in inner ear
with hair cells or cochlear nerve
can hair cells regenerate?
once damaged, no
what does cochlear implant consist of ?
internal and external component
receiver that decodes signal and sends signals to electrode array
where is electrode array from impant inserted into, what does that do?
cochlea through oval window
sits on cochlear duct along CN VIII afferents
electric signals along electrode stimulate a particular cochlear nerve along basilar membrane
array mimics tonotopy, stimulate nerves at discrete frequencies
what activate anterior semicircular canal?
rotation in vertical plane forward
what activate horizontal semicircular canal?
rotation in horizontal plane
what activate utricle?
linear acceleration forward and backward
what activate saccule?
linear acceleration up and down
