Lecture 29: Neuroanatomy of the Auditory and Vestibular Systems Flashcards
3 functions of vestibular system
transduce and interpret head movements
maintain position of visual axes when head is moving = vestibulo-ocular reflex
send motor commands to trunk and limb muscles in order to maintain balance
vestibulo ocular reflex
when head is moving but eyes can still look at target
where are vestibular nuclei located
brainstem
vestibular nuclei receive info from (2)
info on head movement from organs of balance
muscle firing from cerebellum
which region of brainstem coordinates motor output through cortical and vestibular pathways
cerebellum
cerebellum receives info from what 3 regions
cortex
spinal cord
vestibular system
lesions to CN VIII or vestibular nuclei lead to disruptions in (4)
stance
head posture
balance
loss of extensor muscle tone
bony labyrinth: location, definition, what is contained (general)
bony outer shell of deeper membranous labyrinth
within petrous portion of temporal bone
encases inner ear
organs of balance and hearing = vestibular and cochlear organs
what are the vestibular organs (4)
semicircular ducts
utricle
saccule
vestibular nerve
what are the cochlear organs (2)
cochlear duct
cochlear nerve
membranous labyrinth contains
endolymph
region between membranous ducts and walls of bony labyrinth contain
perilymph
endolymph vs perilymph
endolymph = more [K+]
perilymph = more [Na+]
vestibular and cochlear apparatuses rely on what
mechanical displacement of mechanoreceptors by fluid (lymph derivative)
definition of acceleration
rate of change of velocity / time
utricle: definition, function
vestibular organ
monitor and activate response to linear acceleration of horizontal movements relative to gravity (side to side)
saccule: definition, function
vestibular organ
monitor and activate response to linear acceleration of vertical movements relative to gravity (up and down)
3 semicircular ducts: definition, function
vestibular organ
respond to angular acceleration (rotation) of head in all planes = anterior, lateral and posterior semicircular canals
on each side of the head there are (6)
3 semicircular ducts each with 1 ampulla
1 utricle with 1 macula
1 saccula with 1 macula
1 vestibular ganglion
ampulla =
dilation
vestibular ganglion =
scarpa’s ganglion
where are semicircular hair duct cells location
within ampulla
effect of moving endolymph on cupula, stereocilia, kinocilium
bends capula
tilts stereocilia and kinocilium of hair cells
semicircular duct hair cells general anatomy
cell body
stereocilia and kinocilium in contact with endolymph
effect of displacement of specialized hair cells during movement (hint: changing membrane potentials)
opens mechanically gated K+ channel = depolarizes = more voltage gated Ca channels open = increases glutamate release
depolarization vs hyperpolarization effect on channels
depolarization - more APs, open channels
hyperpolarization - less APs, close channels
hair cells are located in which organs/areas (5)
semicircular duct
otolith organs = utricle, saccule
otolithic membrane
otoconia
macula
otolith organ displacement process
moving head allows displacement of gelatinous cap –> cap moves and tilts stereocilia toward kinocilium –> hair cells depolarize = opens channels
mirrored orientation of hair cells in macular organs
some hair cells depolarizing while others are hyperpolarizing
reversal line indicates this separation
opposite polarity of hair cells: effect on firing rate, what side of head
depolarize on side of head toward which person is turning = increase firing rate of hair cells
hyperpolarize on side of head from which person is turning = decreased firing rate of hair cells
relationship between magnitudes of firing rates in semicircular canals
should be equal
hyperpolarization = depolarization
which nuclei compares the firing rates from each side
vestibular
what must happen to redirect eyes when head rotates: vestibuloocular reflex (2)
motor commands to contract left lateral rectus muscle
motor commands to contract right medial rectus muscle
lesions of vestibular portion of CN VIII, vestibular apparatus or vestibular nuclei
imbalance of APs received by vestibular nuclei
perception of moving when NOT
function of auditory system
transduce and interpret vibrations due to sound
which labyrinth contains sound transduction mechanism
cochlear
position of cochlea relative to semicircular ducts
rostromedial
sound transduction mechanism in cochlea
footplate of stapes transmits vibrations to membrane of oval window and perilymph of scala vestibuli
fluid displacement from oval window creates
waves and displacements in membranes of cochlea
scala vestibuli is filled with
perilymph
what mechanism does hearing use for transduction
same as vestibular system = mechanoelectrical
stereocilia of hair cells are displaced
neural sensation of hearing mechanism
displacement of tectorial and basilar membranes move stereocilia –> transduction of hair cell
effect of varying material properties of basilar membrane
allows propagation of various waves in specific regions
sensitivities to certain frequencies in certain parts of basilar membranes –> brainstem nuclei
interaural time differences used to compute location based on
timing differences between each side
interaural level differences used to compute location based on
sound level differences received between each side (directionality)
2 differences used to determine where sound came from
interaural time
interaural level
