Vestibular System Flashcards
What is the vestibular apparatus comprised of?
three semicircular canals and the utricle and saccule.
What doe the 2 otolith organs (utricle and saccule) of the vestibular apparatus do?
detect linear accelearations and head tilts
What do the semicircular canals do?
detect rotational movement
The vestibular part of CN 8 goes to what ganglion?
Scarpas ganglion
What three major nerves come into the vestibula and cochlea?
vestibular part of CN 8
Auditory part of CN 8
Facial nerve
If you have an overproduction of endolymph, where will you have a probleM?
in both the vestibule and the cohlea
is the saccule superior or inferior to the utricle?
inferior
What are the saccule and utricle filled with
big hair cells that respond to deflections of the head movements (vertical acceleration and linear acceleration)
Hair cells in the vestibular apparatus are similiar to those in the auditory system. T or F?
T
Describe the hair cells of the vestibule
they have on kinocilium and have ca ion channels and are bathed in fluid.
In the ampulla, what are the hair cells embedded in?
the cupula (a gelatinous mass)
In the Utricle and Saccule, what do the hair cells extend into?
into a gelatinous mass with otoconia (little stones) on top
Hair cells in the cupula are excited or inhibited when fluid moves around the (blank) during rotations.
semicircular canal
Hair cells in the utricle and the saccule are imbedded in the (blank) membrane with little stones on top.
otolithic
How do you get the otoconia to move and elicit a response in the hair cells of the utricle or saccule?
the stones move due to the effects of gravity or linear accelerations and cause the hair cells to fire
Explain the sensory layer of the utricle and saccule
otoconia
otolithic membrane, gelatinous layer
reticular membrane (hair cells here)
supporting cells
The hair cells in the ampulla are all oriented how?
the same way
The hair cells in the utricle and the saccule are oriented how?
opose each other (posterior opposes anterior)
Explain the sensory pathway for the semicircular canals, utricle and saccule.
hair cells-> vestiblar ganglion-> vestibular nerve-> inferior and medial vestibular nucleus
What can you find next to the inferior cerebral peduncle?
inferior and medial vestibular nucleus
dorsal and ventral cochlear nucleus
How do the fibers of the vestiblar nuclei get to the upper spinal cord and what do they do there?
via the medial vestibulospinal tract ( a bilateral path)
control axial musculature involved in head and upper trunk turning
how do fibers of the vestibular nuclei project to the spinal cord and what do they do there?
via the lateral vestibulospinal tract (ipsilateral pathway) and contols proximal anti-gravity muscles
How do fibers of the vestibular nuclei get to the parietal sensory cortex and what do they do there?
via VPL in thalamus
supply info for planning movements based on the position of the body in space
Where do fibers of the vestibular nuclei go in the branstem?
to motor nuclei of 3,4,6 to coordinate eye movements with head movments (VOR)
So where all do fibers of the vestibular nuclei project to?
upper spinal cord spinal cord cerebellum thalamus brainsem motor nuclei
What spinal tracts help to maintain posture when you slip on ice?
medial and lateral vestibulospinal
The projections to and from the cerebellum provide the cerebellum with information about (blank)
body position for proper coordination of future movements
Explain how vestibular projections get to the cortex
lateral and superior vestibular nuclei go to the cerebrum where it synapses in the VP nucleus of thalamus and then goes to the vestibular cortex in postcentral gyrus
Explain how the you get vestibular projections to the cerebellum and back
Afferent pathway: spinal cord-> lateral vestibular spinal tract-> synapses mid pons at the lateral vestibular nucleus-> cerebellum
Efferent Pathway:
Cerebellum-> rostral medulla at medial vestibular nucleus-> descend to spinal cord via the MLF
Explain how you get vestibular projections to CN nucleis 3,4 and 6 (VOR)
Scarpas ganglion (cell bodies of primary afferent neurons of hair cells) -> medial vestibular nucleus-> abducens nucleus-> medial longitudinal fasiculus-> oculomotor nucleus-> muscles OR scarpas-> medial vestibular nucleus-> abducens straight to LR
Where is the abducens nucleus?
Where is the oculomotor nucleus?
in the pons
midbrain
This is an important integrating nucleus for CN 3,4, 6 and allows you to give horizontal eye movements. Anything coming out of the cortex or vestibular before hitting up 3 4 6 must pass through this. What is this?
PPRF
(blank) carries information about the direction that the eyes should move.
It connects the cranial nerve nuclei III (Oculomotor nerve), IV (Trochlear nerve) and VI (Abducens nerve) together, and integrates movements directed by the gaze centers (frontal eye field) and information about head movement (from cranial nerve VIII,
MLF (medial longitudinal fasciculus)
Below the brainstem the desc. MLF becomes the (blank)
medial vestibulospinal spinal tract
When you move your head, the (blank) will move oppsite the movement of your head.
endolymph
Kinocilia always face what?
the utricle
Fluid movement towards the ampulla is (blank) and movement away is (blank)
excitatory
inhibitory
If you excited your hair cells what will you have in increase in firing of?
vestibular nerve
Does the abducens nucleus control the ipsilateral or contralateral motor nucleus?
contralateral
Describe the pathway of the vestibulooculoreflex when you move your head to the right
(you shake your head but maintain the direction of your eyes involuntarily)
your endolymph will flow to the left which will stimulate those hair cells which then synapse in the vestibular nuclei and cross to the PPRF and then go into abducens where they decussate and enter the oculmotor OR go straight to LR.
Describe the pathway of voluntary eye movement
Frontal lobe-> PPRF-> which goes to abducens nucleus to ether LR or to oculomotor nucleus (CN 3) to MR
So what happens if you damage the left vestibular nucleus/nerve?
Your left side will lose all drive and your right vestibular nuclei becomes dominant and thus your eyes drift to the left and when they get all the way over and then snap back and its starts all over again. It snaps back because of cortical input to the system (voluntary eye movement). This is nystagmus
What happens if you have a cortical legion?
you lose your ability to utilize the voluntary pathway so you cant snap your eyes back
Why do your eyes drift when you have a vestibular nerve/nucleus legion?
because the remaining nucleus will continue firing causing drifting to the opposing side.
How can you remember how cold water will make your nystagmus (i.e the snap back movement) move?
COW
Cold opposite Warm same
SO what do your eyes look like if you are in a comatose state and have your brain stem intact and someone throws cold water in the ear?
your eyes will move slowly toward the ear you put cold water into but you will lose nystagmus so your eyes wont snap back
So what do your eyes look like if you are in a comatose state and you have a MLF lesion (bilateral) and someone throws cold water in your ear?
Why?
only the ear closest to the ear with water in it will move laterally.
because your MLF is what links your abducens nucleus to the oculomotor nucleus SO if you lose your MLF only your abducens will be intact.
If you have a bilateral lower brainstem lesion, what would your eye movements look like when cold water is put in your right ear?
No movement at all in either direction; lower brainstem bilaterally would sever both vestibular nuclei connecting to PPRF, therefore you wouldn’t get any input to create the slow portion of the VOR>
A lesion in abducens leading to lateral rectus paralysis only would be upper or lower motor neuron?
Lower motor neuron
A lesion in the MLF connecting abducens to oculomotor would be an upper or lower motor injury?
Upper
Can you still converge on a single point after an MLF injury?
YES, convergence enters oculomotor from a separate pathway!
A lesion in the right eye frontal field area of the cortex would cause what changes in eye movements?
You would lose voluntary ability to move your left eye laterally and right eye medially (so both eyes to the left) and loss of nystagmus
A lesion at the left PPRF would have what effects on eye movements?
Loss of left lateral rectus and right medial rectus, but nystagmus would be intact
What are the frontal eye fields?
Cortical areas responsible for giving motor efferents to voluntary eye movements (i.e right frontal eye field moves both eyes to the left)
