MODULE 7- The Vestibular System Flashcards
translational movements
forward linear motion
the vestibular system does what
helps us sense our position + movement in space
rotational movements
turning movements of the head
gravity
tilt of the head
____ uses ____ to translate physical movement into neural impulses (electrical energy)
-labyrinth
-hair cells
what is located outside of the bony labyrinth
perilymph
what is located inside the labyrinth
endolymph
how many otolith organs
2
2 otolith organs
-utricle
-saccule
what do the 2 otolith organs do (utricle/saccule)
respond to translational movement + to gravity (head tilt)
how many semicircular canals
3
what do semicircular canals do
respond to rotations of the head
ampullae
located at the base of the semicircular canals
what does the ampullae house
hair cell bundle
hair cell bundle
bathed in endolymph
roll
rotation around x-axis
yaw
rotation around z-axis
pitch
rotation around y-axis
what responds to linear acceleration
utricle + saccule
what responds to rotational acceleration of the head
semicircular canals
linear acceleration is head angle relative to ____
gravity
vestibular hair cells
transduce minute physical displacements of hair cell bundles into electrical receptor potentials
stereocilia tips have ____
ion tranduction channels
stereocilia tips- ion movement in one direction -> depolarization/hyperpolarization
depolarization
stereocilia tips- ion movement in opposite direction
-> depolarization/hyperpolarization
hyperpolarization
vestibular hair cells transduce mechanical stimuli into ____
receptor potentials
hair cells
-in vestibular labyrinth
-transduce mechanical stimuli into neural signals
head movement leads to
deflection of the hair bundles in the receptor organ
deflection TOWARD the kinocilium causes cell to depolarize/hyperpolarize
depolarize
-and thus increases the rate of firing in the afferent fiber
bending AWAY from the kinocilium causes the cell to depolarize/hyperpolarize
hyperpolarize
-and thus decreases the afferent firing rate
in the ampulla located at the base of each semicircular canal, how are hair bundles oriented
in the same direction
in the sacculus + utricle, the ____ divides the hair cells into populations with opposing hair bundle polarities
striola
in the sacculus + utricle, the striola divides the hair cells into populations with ____
opposing hair bundle polarities
otolith organs
the utricle + saccule
what do the utricle + saccule sense
static tilt + dynamic linear movements
macule
contains hair cells + supporting cells
what does the macule have
an overlying gelatinous layer
otolithic membrane
overlying the gelatinous layer
otoconia
calcium carbonate crystals embedded in the otolithic membrane
what 2 things does the macula contain
-the hair cell
-supporting cells
otolith organs (utricle + saccule)- translational movements or head tilt (gravity) cause what
shearing forces between the macula + membrnae ->
receptor potentials in the hair cells
utricle is sensitive to vertical/horizontal accelerations
horizontal
saccule is sensitive to vertical/horizontal accelerations
vertical
striola
divides the hair cells into populations with opposing hair bundle polarities
how many sensory organs are there for the 3 axes of linear motion
2
in an upright individual, the macula of each utricle/saccule is approximately horizontal
utricle
in an upright individual, the macula of each utricle/saccule is oriented vertically
saccule
in this posture, the saccule can sense ____ accelerations in its plane
linear accelerations
-up-down
-forward-backward
in this posture, the utricle can sense ____ accelerations in its plane
linear
-left-right
-fowrard-backward
what do otolith do
register forces related to linear acceleration
-responds to both linear head motion + static tilt with respect to the gravitational axis
e.g., during flight at a constant velocity, we have no sense that we are traveling at 300 miles per hour
-however, in the process of taking off, we sense the change in velocity (acceleration)
-the otoliths differ from the semicircular canals: they respond to linear motion instead of angular motion
the same shearing force acting on vestibular hair cells can result from tilting of the head (top), which exposes the hair cells to a portion of the acceleration
(a) owing to gravity (Fg), or from horizontal linear acceleration of the body (bottom)
-in this case, the postural system cannot distinguish between tilt + linear acceleration of the body based on otolithic inputs alone
nerve fibers have a ____ firing rate when the head is upright
steady
what 2 things can change in firing rate reflect
-sustained (absolute head position)
-transient (linear acceleration)
firing rate is tilt ____-dependent
direction
each of the 3 semicircular canals has ____ at the base that houses the ____
-ampula
-crista (sensory epithelium)
angular acceleration in 1 direction causes what
causes endolymph to displace the cupula in the opposite direction
each ____ on opposite sides of the head results in opposite changes in their firing rates
“partner” of semicircular canals
cilia are arranged in ____
size
tallest cilia
kinocilium
how are cilia arranges
kinocilium (tallest) to shortest cilium
____ house the bipolar neurons that give rise to the vestibular ranch of cranial nerve VIII
vestibular nerve ganglion (Scarpa’s ganglion)
vestibular nerve ganglion (Scarpa’s ganglion) house what
bipolar neurons that give rise to the vestibular branch of cranial nerve VIII
vestibular nerve ganglion (Scarpa’s ganglion) distal processes innervate what
semicircular canals + otolithic organs
vestibular nerve ganglion (Scarpa’s ganglion) central processes project via
via vestibular portion of vestibulocochlear nerve (VIII) ->
vestibular nuclei (also directly to the cerebellum)
what does optic flow help to maintain
a sense of self-motion
optic flow
in addition to activating the vestibular system, translational movements also generate a visual motion pattern across the retina
-helps to maintain a sense of self-motion
vestibular-ocular reflex (VOR)
helps maintain a steady image on the retina while moving the head
vestibular-ocular reflex (VOR) ex
rotation of the head ->
left vestibular nucleus activity ->
compensatory eye movements to the right
the vestibulo-ocular reflex (VOR) stabilizes what
stabilizes the eyes when the head moves
oscillopia
-loss of VOR
-inability to fixate on visual targets while the head is moving
postrual adjustments of the head are mediated by what
vestibulocervical reflex (VCR)
what must change when one wears eyeglasses
the gain of the VOR
what do eyeglasses change
the size of the visual scene
postural adjustments of the body are mediated by what
vestibulospinal reflex (VSR)
VCR (vestibulocervical reflex) pathway
medial vestibular nucleus ->
MLF ->
upper cervical spinal cord
VSR (vestibulospinal reflex) pathway
medial vestibular nucleus ->
lateral + medial vestibular spinal tracts ->
lateral + medial verntral horn, respstively, to innervate proximal + axial limb muscles
VSR (vestibulospinal reflex) provides excitatory infleunce on what muscles
extensor (antigravity) muscles
reflex that stabilizes head
vestibulo-cervical reflex, VCR
VCR is medial/lateral
medial
what reflex maintains postural balance
vestibulo-spinal reflex, VSR
VSR is medial/lateral
lateral
vestibular pathways to the thalamus + cortex
lateral + superior vestibular nuclei ->
thalamic ventral posterior nucleus ->
parietoinsular vestibular complex (PIVC) ->
Brodmann’s areas 3a + 2v
what is PIVC important for
sense of self-motion + body orientation in extrapersonal space
when are neurons in PIVC activated
when visually tracking a moving object + by rotation of the body (even when the eyes are closed)
neurons in cortical areas also respond to what stimuli
proprioceptive + visual
stimulating the PIVC elicits what
strong vestibular sensations
physiological nystagmus
normal
-slow compensatory eye movements in response to turning the head
spontaneous nystagmus
-eyes move from side to side in the absence of any head rotation
-slow eye movement toward the damaged side
-fast eye movement away from the damaged side
what causes pathological nystagmus
unilateral vestibular hypofunction
pathological nystagmus- slow phase directed toward which side
lesioned side
pathological nystagmus- quick phase direct toward what side
intact side (reset)
