Physiology of the Auditory and Vestibular Systems Flashcards
What is the makeup of endolymph?
high K
low Na
found in scala media
What is the makeup of perilymph
low K
high Na
found in scala vestibuli and scala tympani
bathes basal end of cochlear hair cells
How do sound waves go through the cochlea?
tympanic membrane –> malleus –> incus –> stapes in oval window –> scala vestibuli –> cochlear duct –> basilar membrame –> scala tympani –> round window
What is the basilar membrane like in proximal and distal parts and how does this affect the frequency of waves that go through it?
near oval window: narrow and stiff –> high frequency waves go here
near helicotrema: wide and flexible –> low-frequency waves go here
What types of cells are hair cells?
specialized epithelial cells = mechanoreceptors
receive afferent and efferent input, but themselves are NOT neuronal
Where are stereocilia on hair cells?
on the apical surface
stiff, graded in size, rich in actin
neural synapses on basal side
What is a kinocilium?
the tallest cilia
stereocilia bend in direction of of kinocilium –> depolarizes cells
How do hair cells depolarize and signal?
stereocilia are deflected in direction of the kinocilium –> K+ ions enter cell and depolarize it –> voltage-gated Ca channels open –> vesicles w/ glutamate are released –> post synaptic afferent neuron
What 2 things drive the depolarization of hair cells?
endolymph is high in potassium = concentration gradient
large electrical gradient = scala media has high positive charge
Where are the stereocilia of hair cells located?
Where is the rest of the cell located?
stereocilia in endolymph
rest of cell is in perilymph
What connects stereocilia?
topconnector chains
if one hair is deflected –> they all move
What is the difference between excitation and inhibition hair cell signalling?
excitation: cilia deflect toward kinocilium –> depolarization –> increase in APs
resting = basal tone of APs
inhibition: cilia deflect away from kinocilium –> hyperpolarization –> decrease in AP freqeuncy
What lets K+ into hair cells?
TRPA1 channel
What NT do hair cells release?
glutamate
What is the stria vascularis?
specialized epithelium of scala media
pump K into endolymph to maintain electrochemical properties of the endolymph
What is the composition of hair cells on the basilar membrane?
one row of inner hair cells = primary source of auditory info
3 rows of outer hair cells = amplifier, contractile bc of prestin proteins –> boost mechanical vibrations of basilar membrane; susceptible to injury
What is the difference in innervation of inner and outer hair cells?
outer: get both efferent and afferent I from type II affererents
inner: just afferents from type I
Which hair cells bend first?
outer first –> then inner
How is the cochlear nucleus divided?
dorsal cochlear nuclei: integrates acoustic info w/ somatosensory info to localize
ventral cochlear nuclei: begins processing temporal and spectral features of sound
What is the significance of the superior olivary complex?
first site in the brainstem where info from both ears converges = binaural processing
MSO = primary nucleus
receives excitatory (glutamate or aspartate) projections from cochlear nuclei
What does the medial superior olivary nucleus (MSO) do?
generates a map of the interaural TIME differences to help localize sound
responds strongest when the 2 inputs arrive simultaneously, which occurs when 2 sides compensate for microsecond differences in the time of arrival of the sound at the 2 ears
What does the lateral superior olivary nucleus (LSO) do?
generates a map of the interaural INTENSITY differences to help localize the source of a sound
side of sound localization –> excites ipsi LSO –> receives inhibition from contra side; but net excitation > inhibition
What do the inferior and superior colliculi do in hearing?
IC: suppresses info related to echoes, which would interfere w/ localization and arrives at final est of localization along horizon
SC: takes location data from IC –> adds vertical dimension = spatial map
What does the MGN of the thalamus do in hearing?
relay station (from inf colliculus)
tonotopic map is maintained
processing features of speech inflections
Where is the primary auditory cortex (AI)?
post part of sup temporal gyrus
essential in conscious perception of sound
higher order processing
tonotopic map is maintained
Where are low and high frequencies located in the primary auditory cortex?
anterior = low freq (apex of cochlea)
posterior = high freq (base of cochlea)
What does the auditory association complex do?
broca’s and wernicke’s, others
less specifically organized in tonotopic arrangement than primary
thought to respond to more complex sounds, IDing a sound, speech
What are olivocochlear efferents?
originat in Superior olivary complex
Medial OC –> innervate outer hair cells
Lateral –> inner hair cells
LIMO
What is the function of olivocochlear efferents?
shifts responses to higher sound levels
decrease adaptation
reduce the response to noise
may protect hair cells from damage
What are otoacoustic emissions?
ear can emit sound, but usually inaudible
spontaneous OAE: in 1/3 of normal ppl
Evoked: used to test for hearing loss (no emissions evoked if damage present)
evoke on newborns
What is sensorineural hearing loss?
caused by damage to hair cells or nerve fibers
noise damage, ototoxic drugs, etc.
Outer HCs more susceptible than inner
base (high freq) more susceptible
What is the difference in effect of damage to inner vs outer hair cells?
injury to outer –> decrease in sensitivity and broader tuning
injury to inner –> cuts off auditory input to CNS
What is a cochlear prosthesis?
multiple electrode array threaded through cochlea to stimulate surviving nerve fibers
What motion do the semicircular canals detect?
rotational acceleration
What motion do the otolith organs detect?
utricle: linear acceleration forward and backward
saccule: linear acceleration up and down
What does each semicircular canal detect?
horizontal: rotation in horizontal plane
posterior: rotation in saggital plane backward (falling back)
anterior: rotation in saggital plane forward
What muscle is activated when the horizontal canal is firing?
medial rectus m is active and lateral rectus inhibited (in eye ipsi to rotation)
What muscles are activated whn the posterior canal is firing?
falling back
superior oblique active and inferior oblique inhibited
(eyes ove down to focus on a point as you fall back)
What muscles are activated when the anterior canal is firing?
falling forward
superior rectus activated
inferior rectus inhibited
How does head rotation affect the hair cells?
turn away from ear –> hair cells pushed away from king bc of endolymph pressure –> inhibitory signal
turn head toward ear –> hair cells pushed toward king –> excitatory signal
