auditory & vestibular physiology Flashcards
what fluid bathes the apical end of hair cells
endolymph
what is the ionic makeup of endolymph
high K
low Na
what is the ionic makeup of perilymph
low K
high Na
what fluid bathes the basal end of hair cells
perilymph
where is endolymph found within the cochlea
scala media
where is perilymph found within the cochlea
scala vestibuli
scala tympani
axons of the spiral ganglion project to the brainstem via what nerve
auditory nerve (aka cochlear branch of CN VIII)
where do higher frequency sounds maximally displace the basilar membrane
at the base
near the helicotrema, do higher or lower frequency sounds maximally displace the basilar membrane
low frequency
near the oval window, do higher or lower frequency sounds maximally displace the basilar membrane
higher frequency
where is the basilar membrane narrow and stiff
at the base, near the oval window
where is the basilar membrane wide and flexible
at the apical end, near the helicotrema
what kind of cells are hair cells
mechanoreceptors (specialized epithelial cells)
what fluid are the cilia of the hair cells bathed in
endolymph
what drives potassium into the hair cell
potassium concentration gradient (low K at the basal side of the hair cell) electrical gradient (high positive charge within scala media)
what does the potassium influx of the hair cell cause
depolarization of the cell => opening of voltage gated Ca channels
what does the calcium influx of the hair cell cause
realease of glutamate to afferent n. => spiral ganglion
what occurs following deflection of hair cell cilia TOWARDS the kinocilium
depolarization
what occurs following deflection of cilia AWAY FROM the kinocilium
hyperpolarization
through what channels does K enter the hair cells
TRPA1
what causes TRPA1 channels to open
when cilia deflects toward kinocilium, chain of proteins open TRPA1
what structure maintains electrochemical properties of endolymph
stria vascularis
what do inner hair cells do and how are they arranged
primary source of auditory information
arranged in one row along cochlear spiral
what do outer hair cells do and how are they arranged
act as an amplifier - boost or dampen mechanical vibrations of basilar membrane
arranged in three rows along cochlear spiral
from where do hair cells receive efferent innervation
superior olivary complex
from where do hair cells produce afferent innervation
spiral ganglion
what are type II afferent neurons
single afferent from many outer hair cells => brainstem
what are type I afferent neurons
neurons from one or more inner hair cells => brainstem
what happens after sound hits the stapes?
pressure within scala vestibuli falls below that of scala tympani
what happens as a result of decreased pressure in the scala vestibuli
basilar membrane bows upward => organ of corti shears toward hinge or tectorial membrane
what protein facilitates contractile activity of outer hair cells
prestin
what occurs as a result of shearing of the organ of corti
cilia of over hair cells tilt toward kinocilium => K+ channels open and cell depolarizes
what occurs as a result of depolarization of outer hair cells
contraction of prestin protein => accentuated upward movement of basilar membrane, making waves in endolymph
what occurs as a result of waves in the endolymph hitting the tectorial membrane
inner hair cells bend toward kinocilium, TRPA1 channels open => => glutamate released
what is the first site within the brainstem where information from both ears converges
superior olivary complex
what nucleus generates a map of interaural time differences and why
medial superior olivary nucleus (MSO)
helps w/ localization
what nucleus generates a map of interaural intensity differences and why
lateral superior olivary nucleus (LSO)
helps w/ localization
how does the inferior colliculus perform horizontal localization
by suppressing information relating to echoes
what occurs at the superior colliculus within the auditory pathway
vertical height is added to the information received from inferior colliculus, creating a spatial map of sound location
which part of the primary auditory cortex is activated by low frequency sounds
more rostral (anterior) areas
which part of the primary auditory cortex is activated by signals from the base of the cochlea
more caudal (posterior) areas
what are the three sources of efferent input to the auditory system
- olivocochlear efferents
- middle ear muscle motor neurons
- autonomic innervation of inner ear
between what structures do medial olivocochlear efferent travel
superior olivary complex => OUTER hair cells
between what structures do lateral olivocochlear efferent travel
superior olivary complex => inner hair cells
what is the function of olivocochlear efferents
shifts responses to higher sound levels and reduces response to noise
what is the function of middle ear efferents
prevent damage by decreasing transmission of loud sounds
what are the two middle ear efferents and from what CNs do they arise
tensor tympani from CN V
stapedius from CN VII
in what situations are otoacoustic emissions seen
evoked OAE are normal in people without hearing loss
what is measurement of OAE used for
- newborn hearing screen
- evaluation of tinnitis
- evaluation of possible ototoxicity
are outer or inner hair cells more susceptible to damage
outer hair cells
what is the result of injury to inner hair cells
cuts off auditory input to CNS
how do cochlear prostheses work
electrodes in cochlead stimulate nerve fibers
what sensation do the semicircular canals detect
rotation
what sensation does the utricle detect
linear acceleration forward and backward
what sensation does the saccule detect
linear acceleration up and down
which semicircular canal best detects rotation in the vertical plane BACKWARDS
posterior semicircular canal
which semicircular canal best detects FORWARD rotation in the vertical plane
anterior semicircular canal
what muscles are active/inhibited when you fall forward
active: superior rectus
inhibitied: inferior rectus
eyes move UP
what muscles are active/inhibited when you fall backward
active: superior oblique
inhibited: inferior obligue
eyes move DOWN
what muscles are active/inhibited in the eye ipsilateral to rotation when spinning
active: medial rectus
inhibited: lateral rectus
contralateral eye does the opposite
what fluid surrounds the vestibular apparatus
perilymph