Section 3 Vestibular System Flashcards
Vestibular fxns:
stabilization of eye position, perc of body rotation and translation, visual and postural vertical perc
Disorders of the vestibular system:
Meniere’s disease, Benign Paroxysmal Positional Vertigo (BPPV)
BPPV is more common as:
you age
What signal the static position of the head with respect to gravity and its linear acceleration?
Utricle and saccule
What signals rotation and angular acceleration of the head?
Semicircular canal
Names of the 3 loops of the semicircular canal:
ant, pos, and lateral
What regions of the ear contain hair cells?
Cochlea? (check)
The utricle detects:
linear accelerations and head-tilts in the horizontal plane.
The saccule detects:
linear accelerations and head-tilts in the vertical plane.
Where are the axons of the utricle located?
Trick Question. There are none
Explain the transmission of info from the hair cell in the utricle.
Synaptic vesicles in body of hair cell release glutamate on 8th nerve afferents which send info about these organs to the brain
How many 8th nerve afferents are connected to each hair cell?
1 in the images in slides
At which end of the hair cells are the hair bundles?
Apical end
What are the tips of the hair cells embedded in?
Otolithic membrane, gelatinous structure overlying the hair cells
Fxn of otoconia:
to add extra weight to the structure
What are found on the otolithic membranes in the utricle?
Otoconia (Ca carbonate crystals)
Endolymph has a high conc of what ion?
K+, positively charged
What are the hair bundles surrounded by?
endolymph
2 different ECF involved w hair cells:
Endolymph, high K+ and positively charged (top of the structure) and perilymph, high Na++ and low K+, surrounding the hair cell bodies
Effects of tilting head:
tilt membrane that is mechanically coupled to the bone that surrounds the structure
What causes distortion of the otolithic membrane?
weight of the otoconia when tilting head
Linear acceleration:
distortion of the hair cell with respect to body, epi moves in same direction as head bc they are mechanically connected, bending of the hair bundles
What causes the hair uncles to bend during acceleration?
the inertia of the heavy crystals that accelerate more slowly than the hair cell bodies
How many kinocilium per hair strucutre are there?
1
Kinocilium is aka:
true cilium
Where are kinocilium located?
all vestibular hair cells
How are the hair stereocilia arranged?
Same height L to R - polarized, short to tall in other direction, affects how each of the hair cells work
Fxn of step-like arrangement of stereocilia of the hair cell:
How moves of upper part of structure triggers electrical changes to go to the CNS (check)
About how many stereocillia are there?
60
What system is the kinocilium related to:
vestibular
How are the stereocilia arranged?
Step-like
How are adjacent stereocilia of the hair cell attached?
Tip links
Where do tip-links attach to the stereocilia?
locations of mecahno receptor channels
Fluid bathing the stereocilia:
endolymph, K+ is the predominant ion that will be flowing in (Ca as well, but mainly K)
What 2 ions can flow into the stereocilia?
Ca and K
What is the extracellular fluid of the inner ear?
endolymph
Disorders of the endolymph:
disruption of endolymph production or hair cells fxn
Disruption of endolymph production can lead to:
Vertigo, vomiting, hearing impairment
What can cause the disruption of endolymph production?
inflammation of the inner ear
Meniere’s disease:
disruption of the hair cell fxn, attacks w no warning, last hours
Possible causes of Meniere’s disease:
head trauma, virus, or rise in endolymph volume due to hole in membrane separating endolymph and cochlea fluids OR improper endolymph drainage
What is the hair cell potential?
-50mV, bc cell is slightly depolarized due to the tugging on membrane that open mechanoreceps allowing K to enter
How do the hair cells activate its afferents?
NTs
When will there be no volvtage change in hair cell receps?
Orthogonal (R angle) tilt
When is the 8th nerve firing rate at its greatest?
When the hair fibers are flowing in the opposite direction of the 8th nerve., largest space bw stereocilia opening more channels
When is the 8th nerve firing rate at its least?
hair fibers tilted in direction of the 8th n.
How is the 8th n. firing when there is no movement of the hair cell?
active signal that says that nothing much is happening
How can direction be conveyed via the hair cells. How do the cells transmit this info differently?
When not moving there is an intermediate firing rate, when pushed in either direction the firing rate will either increase or decrease making directional differentiation easy
Firing rate of a hair cell at rest:
100 Hz
What NT is used by the hair cells to transmit info?
glutamate
How are the tip links connected in the orthogonal directon (into the plane of the page)?
They aren’t
The utricle can detect head tilt in any direction away from:
vertical
How are the hair cells at different angles in the utricle affected with a tilt of the head?
some depolarize, some hyperpolarize, some not affected
T or F? Hair cells are more sensitive in one direction.
T.
What structure looks just like the utricle but is oriented vertically in the upright head?
Saccule
When does the sacculus sense most effectively?
When the head is on its side
What do the semicircular canals respond to?
Head rotation
How many canals are there on each side?
3: 1 horizontal (L R turning of head), 1 ant and 1 pos duct, both upright, 90’ to each other (X,Y,Z axis)
T or F? Semicircular canals respond to linear and static tilt.
F. head rotation only
Specialized region that contains hair cells:
ampulla
Hair bundles that stick out are assoc w:
cupula (flexible)
What allows for endolymph to participate in the signaling of changes in movement?
it is fluid and not mechanically coupled to the outside structures (i.e. the cupola is coupled to membrane)
What bends in the endolymph with moves?
cupula
A turn to the R depolarizes all the hair cells in the:
R horizontal canal
In which manner are movements of variable speed transmitted?
in a graded manner
T or F? A turn to the R depolarizes ALL the hair cells in the R horizontal canal.
T
This/these structure(s) has hair bundles of only one orientation while this/these structure(s) have hair bundles oriented in all directions.
semicircular canal, saccule and utricle
Where are the larger stereocilia located?
toward the back of the head
When you turn your head to the R will the tip links in the L canal be brought closer together or spread further apart?
closer
When you turn your head to the R will more or less K enter the cilia of the L canal? More or less firing?
less K coming in, less positive charge, and less firing
Turn head to the R:
L horiz canal hyperpol, R horiz canal dep
Turn head to the L:
L horiz canal depol, R horiz canal hyperpol
What will the 8th n. afferent increase or decrease its firing rate in response to?
direction and rate of motion
What does redundancy of info from the 2 sides allow for?
vestibular compensation
2 clases of symptoms related to damage to vestibular canals, otoliths, and/or vestibular n. on one side of the head:
static (seen in absence of head moves) and dynamic (seen w head moves)
T or F? Peripheral damage to the vestibular system can be compensated for.
T
Immediate effects of damage to vestibular canals, otoliths, and/or vestibular n. on one side of the head:
problems w balance, posture, gait, and eye moves
T or F? There is a quick recovery time with vestibular compensation.
F. gradual
T or F? Different symptoms of vestibular compensation recover at different rates.
T
Example of when vestibular compensation is important:
when there are more subtle changes in vestibular input such as a loss of a few hair cells
Likely sites for where compensation occurs:
vestibular nuclei and cerebellum
What fraction of the hair cells die off with aging?
About 1/4
Faction of adults, 65+ that fall each year:
1/3
Leading cause of injury or death for people 65+:
falls
vestibular issue that rises in frequency in the 40’s:
bening parxysmal position vertigo (BPPV)
Cause of BPPV:
detachment of otoconia in the utricle, allowing them to enter a semicircular duct
What causes a person w BPPV to feel like they are spinning?
lodging of Ca carbonate crystal in a position that causes them to incorrectly activate hair cells of the semicircular canal
Tx for BPPV:
Otolith Repositioning Procedure
When does severe vertigo occur for pts with BPPV?
head moves
How is vestibular info distributed?
Widely in the thalamus
Vestibular info can combined with (what?) to maintain balance.
visual and proprioceptive input
What sort of visual and proprioceptive input does the thalamus receive?
visual response to optokinetic stimuli (large field, moving stimuli) and prop to neck m. moves
Large-field, moving stimuli:
Optokinetic stimuli
Somatosensory lesion:
sensation that vertical objects are tilted toward the side of the lesion
What do cells in the somatosensory cortex respond to?
some cell: head rotation, others: head tilt
What is the most common sensation in the cortical vestibular responsive areas?
rotation
T or F? There are only a couple of areas of the brain yielding vestibular sensations.
F many areas
Major vestibular area (concentration) in the cortex:
temporo-parietal and parietoinsular cortex
T or F? Some cells in the cortical vestibular responsive areas have a purely vestibular response.
T. Others are multimodal (visual, prop, vestibular)
posterior T cortical lesions:
impair vestibular-derived saccades
Insulotemporal infarctions may lead to:
a tilted perception of visual vertical and to rotational vertigo in stroke pts
What does an impairment of eye responses indicate?
vestibular signal not working correctly
