Vestibular Flashcards
what are does vestibular system do (4)
- balance
- coordinates head and eye movements to stabilize images on the retina
- muscle tone and posture
- unconscious
what are the movements to hold gaze steady
- vestibular
- visual fixation
- optokinetic
what are the movements to shift gaze
- saccades
- pursuits
- vergence
which CN is used for vestibular and auditory info to be sent to the brainstem
CN 8
what is the peripheral organ of our auditory system
chochlea
what organ transduces rotational movements
semicircular canals
what organ transduces linear acceleration
otolithic organs
each labyrinth has a both and membranous component
-the membranous labyrinth is surround by ______ and filled w/ _______
perilymph
endolymph
the bony labyrinth is etched in _____
and filled w/ ______
bone
perilymph
the membranous labyrinth fits in ______ and filled w/ ______
bony labyrinth
endolymph
what are the membranous parts of the….
vestibule
cochlea
semicircular canals
utricle and saccule
cochlear duct
semicircular ducts
the bony labyrinth is…..
the membranous labyrinth is….
-what do its walls contain
bone
connective tissue and epithelium
-its walls contain the sensory receptors
what are the special sensory receptors that are located in the walls of the membranous labyrinth?
how do we know that these are vestibular hair cells?
hair cells
-specifically, vestibular hair cells receptors bc of the presence of the kinocilium
how will your brain know your head just moved
hair cells get deflected when your head moves
-mechanical stimulation
what occurs between hair cells to ensure that endolymph and perilymph dont mix
tight junctions near the microvillar end of the cells
-forming part of the diffusion barrier btwn endolymph and perilymph
what is deflection of stereocilia towards the kinocilium
what is deflection away
- excitatory (depolarization)
- inhibitory (hyperpolarization)
what are the 2 parts of the vestibular labyrinth
what do they respond to
- otolith organs -responds to linear acc (translations)
- utricle
- saccule - semicircular canals-angular acceleration (rotations)
- ant (sup)
- horiz (lateral)
- posterior
you can experience linear acceleration due to either _____ or _____
translational movement
-horizontal plane (side to side, forward-backward)
gravity
- vertical plane
- tilting
inside each organ is a small patch of sensory neuroepithelium called the ______
macula
the macula contains the ______
hair cell receptors
why do the otolith organs respond to linear acceleration?
they are diff than the semicular canals
the otoliths have otoconia-calcium carbonate crystals, the canals dont
deflection in the excitatory direction means the firing rate is going to go ……
-inhibitory direction, the firing rate is going to go….
up
down
when you tilt your head, gravity will pull ont he otoconical mases which will result in the …
mechanical deflection of the hair cell receptors
when udnergoing a trnslational acceleratoin, you go forward but the heavier otoconia ______, thereby deflecting the hair cell receptors
lag behind
what kind of motion do the saccule sense
what do the utricle sense
up-down
side to side translation and tilt
the utricle’s macula is in the _____ plane and responds best to _____
horizontal
linear acceleratoin due to translational movemnet and gravity
where is the saccule’s macular located on
medial wall of the vestibule, oriented in the vertical plane
in the saccule, how do the hair cells face
what about in the utricle
sacc: hair cells face away from striola
utricle: hair cells face towards striola
how are the hair cells oriented so they allow sensitivity to linear motion in all directions
due to the curvature, hair cells are oriented at different angles
how are the hair cells aligned int he semicicular canals vs the macula
SCC: hair cells aligned in the same direction (good for direction of rotation)
utricle and saccule macula: hair cells on either side of the striola oreinted opposite to each other
are the canals responsive to gravity?
NO1!!! only the otoliths are
what are the the membranous labyrinth of the SCC
ampulla of the semicircular duct
-(contains the hair cell receptors that is surrounded by perilymph and filled w/ endolymph)
what is the patch of sensory neuroepithelium of the ampulla
- where do the hair cell processes project onto
- what is the ampulla filled w/
crista ampullaris
- contains the hair cell receptors
- those hair cells processes project into a gelatinous specialization called the cupula
- filled w/ endolymph
why is the semicircular duct not affected by gravity
bc the cupula and endolymph have the same specific gravity
what can cause BPPV (benign paroxysmal positional vertigo)
the otoconia can get dislodged and migrate into the endolymph of the semicircular duct, causing vertigo and nystagmus (old people)
-makes the canal sensitive to gravity when it normallly only reponds to head rotation
how do we get the vestibular sensory info to the brain (and then to the EOMS)
and wehre?
CN 8 at the junction of the pons and medulla (pontomedullary junction)
how does sensory info from CN8 about head position enter the brainstem
- where does it travel btwn
- where wil it eventually synapse
at the cerebellopontine angle
- btwn the inf cerebellar peduncle and the spinal trigeminal tract
- vestibular nuclei of the rostral medulla and caudal pons located w/in the lateral recess of the floor of the 4th ventricle
hair cell receptors of the crista ampullari sand maculae are innervated by the peripheral processes of bipolar neurons located in _____
scarpa’s ganglion
where is scarpa’s ganglion located in
the internal auditory meatus
what is the superior division of the central process of the vestibular apparatus innervate ?
what does it travel w/
superior canal
lateral canal
utricle
travels with the facial nerve
what does the inf division of the central process of the vestibular apparatus innervate?
what does it travel w/
the saccule and post canal
-travels w/ the cochlear nerve
the peripheral processes of bipolar cells innervate the hair cells int he ______ and ______
-their cell body is where?
maculae (saccule and utricle)
-cell body is in scarpa’s ganglion (in IAM)
the central processes leaving scarpa’s ganglion form the ________.
-this travels through the internal auditory canal w/ CN7, traverses the subarachnoid space, and enters the lateral brainstem at the _______
vestibular nerve (CN 8) -cerebellopontine angle
the central processes of cell bodies in vestibular ganglion synapse in ….
- most go to vestibular nuclei in medulla
2. some go to cerebellum
where are vestibular nuclei located at
rostral/open medulla (and caudal pons)
-located in the LATERAL RECESS in the floor of the 4th ventricle
what are teh 4 parts to vestibular nuclei
superior
inf
lateral
medial
hwere will CN 8 synapse in
lateral brainstem in the lateral recess
where does CN8 enter the brainstem at
what is this between
wehre does it synapse at
the CPA (btwn pons and cerebellum), btwn the ICP and spinal trigmeinal nuclues -synapse on the vestibular nuclei
other CN 8 fibers will bypass the vestibular nuclei completely and instead go through the ____ straight into the cerebelllum
ICP
what are some of the outputs from the vestibular nuclei
- spinal cord
- thalamus
- reticular fomration
- cerebellum
- EOM nuclei
- vestibular nuclei on other side
the secondary vestibular fibers project to the ____
- they are thought ot be involved in what
- how
cord
- feedback circuits, important for making fast compensatory postural adjustments in response to something that’s thrown you off balance
- activate limb extensor (antigravity) muscles
what does the lateral vestibulospinal tract do
is it crossed or uncrossed
- facilitates the activation of limb extensor (antigravity) muscles when the OTOLITH ORGANS signal deviations from stable balance and upright posture
- uncrossed
the medial vestibulospinal tract does what?
crossed or uncrossed?
what is it a part of?
- regulates head position by reflex activation of neck muscles in response to the stimulation of semicircular canals resulting from rotational accelerations of the head
- crossed and uncrossed
- part of the MLF
where do the lateral vestibulospinal tract synapse at
extensory motor neurons at all cord levels
-keeps your stance and balance
where does the medial vestibulospinal tract synapse at
on extensor motor nuerons in cervial and thoracic regions for head/neck adjustments
after the thalamus, vestibular info heads to the vestibular cortex which is in the….
post central gyrus of the parietal lobe
then to VP thalamus then to vestibular nuclei
all sensory info must synapse in ____ before being allowed to continue on to cortex
thalamus
the response of the secondary vestibular fibers can be…
- VOR vestibular ocular reflex (horizontal and vertical)
- or physiologic nystagmus
which CN do vertical and torsional eye movements (SR, IR, SO, IO)
which CN do horizontal eyemovements (MR, LR)
CN 3 and 4
CN 6 and 3
do the pathways for VOR synapse at the thalamus/cortex?
no
the angular vestibulo-ocular reflex is a dysnaptic neural reflex that connects the ____ to the ______ CN nuclei
-what do these respond to
semicircular canals to the eye muscle cranial nerve nuclei of 3, 4, 6
-respond to head rotations (specifically angular acc)
what organ is used in the linear VOR
otolith organs (utricle and saccule) which respond to head translations (ex. elevator) and tilts
the horizontal VOR pathway is what kind of head movmenet
-how do eyes move in respect to this
“no, no” head movmeent
- yaw axis
- eyes move away from head movment
the Horizontal VOR is a 3 neuron arc
where is the first order neuron
where is the 2nd
where is the 3rd
1st: cell body in Scarpa’s ganglion (vestibular gang)
2nd: cell body in vestibular nuclei
3rd: CN 6 and CN 3
Horizontal VOR
- what does the peripheral branch of the first neuron innervate
- where will its central branch (CN8) synapse in
- innervates hair cells in the horizontal canals
- its central branch is going to synapse in the medial vestibular nucleus, which is the rostral medulla/caudal pons
where will the 2nd order neurons of the horizontal VOR sned its signal to
across to the abducens nerve ont he other side
-takes innervation from the firs torder neuron, CROSSES over, excites the cells in abducens nucleus
when your head turns to the left, what does it excite? where does that signal go?
excites left horizontal (lateral) canal, that signal comes in, excites the left vestibular nucleus, that sends a signal over to the right abduces nucleus
what CN is in the afferent limb of the horizontal vestibulo-ocular reflex?
what is the efferent limb?
what is the interneurnon
afferent: CN8
efferent: CN 3, 6
interneuron: MLF
what is skew deviation
where does it start and end
a vertical misalignment due to a lesion along the graviceptive pathway which starts in the inner ear (utricle) travels up the entire brainstem and ends in the rostral midbrain (INC)
what is the organization of the crossed oculomotor nuclei
4: SO
3: SR, IR, IO
what does the cerebellum do to the translational movements
cerebellum keeps most of these movements in check such that counterroll is only about 10% of head roll and the vertical displacements are minimal
damage the right ear pathway is equivalent of ____ head tilt
left
in response to the right tilt (roll) what do the eyes do for vertical alignment?
where is the counter roll?
how does the head get tilted?
right eye moves up
left eye moves down
- counter-roll to “left”
- gets tilted opposite (to the left)
in a normal head tilt to right shoulder, what will the elevated eye do? what will the depressed eye do
elevated eye: intort
depressed eye: extort
in utricular pathway for lateral head tilting, utricular projections synapse in the _____ which issues fibers that _______ and ascend in the ____ to the subnuclei of the 4 vertically acting EOMs
vestibular nucleus
cross
MLF
what are the subnuclei of the utricular pathway
the fourth nerve nucleus and the 3rd nerve subnuclei controlling the SR, IR, and IO muscles
-4th nerve nucleus and the SR subnucleus innervate their respective muscles of the contralteral eye
lesion along the “left ear” graviceptive pathway leads to decreased signal. what happens
brain perceives shift and incorrectly assumes head was tilted to right shoulder
-activates the right ear graviceptive pathway to cuase
OD to elevate/intort
OS to depress/extort
