vestib - dysfunction: peripheral vs central Flashcards

1
Q

what is VOR gain

A

eyes move opposite direction to head at same speed
- 1:1

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2
Q

what is the mechanism that triggers 1:1 VOR gain

A

when move, canals polarized and CN 8 fires and velocity, direction, amp of head mvmt is transmitted and will correspond w ms pairs in eyes that will move opposite and proportional to head mvmt

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3
Q

if something is wrong w vestib system how does this impact the VOR gain

A

<1:1
- aka eye velocity < head

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4
Q

what would dysfunction in the VOR present as if the head wasn’t moving

A

eyes moving to opposite side of dysfunction and then bounce back bc realize head isn’t moving bc lost object
==> results in nystagmus

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5
Q

what is spontaneous nystagmus and what path is this seen in

A

eyes going into VOR and then tries to find object again

see in central path, and initially in peripheral path

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6
Q

what is the purpose of a tonic firing rate and what is unique ab this vestibular system characteristic

A

allows for equal and opposite signals on R and L and detects loss of function if something goes wrong

other sensory systems in body won’t be able to detect absence of input the way that vestib can d/t this

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7
Q

SCC orientation and complimentary pairs

A

ant & post canals
- vertical
- 90deg from each other
- 45 deg from sagittal

R post canal + L ant canal
R ant canal + L post canal

lateral canals
- horizontal
- 30deg inclined

R + L lateral canals

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8
Q

how does head rotation impact complimentary canal pairs

A

ipsilateral post excited
contra ant inhibited

ipsi lat excited
contra lat inhibited

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9
Q

what is the push and pull arrangement

A

equal and opposite response of complimentary canals
- ipsi inc firing, contra dec firing

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10
Q

what role do the stereocilia and kinocilium play in the push and pull mechansim

A

stereocilia arranged so that paired canals when one stim, ipsi CN excited and contra is inhibited
- happens bc of how kinocilium are moving away or toward stereocilium

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11
Q

what happens at head velocities >100deg/sec and what does this mean

A

inhibited nerve driven to zero at head velocities >100deg/sec

1/2 of vestib system unable to quantify head mvmt velocities >100deg/sec

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12
Q

why is there an inhibitory cut-off and what does this mean in a healthy vestibular system

A

The inhibited side can only decrease to zero from a resting firing rate of 70-100 spikes/second. Therefore, if movement is > than that, the inhibited side provides no additional information.

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13
Q

inhibitory cut-off impact in a healthy vestibular system

A

still getting input from excitatory side
- how brain knows the stim CN8 is excited
- brain perceives asymmetry and knows head is moving

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14
Q

inhibitory cut-off impact if R vestib side isn’t funtioning and what is the result and what has to potential to modulate that result

A

if turn head >100deg/sec to R, wouldn’t get excitatory firing
- still see inhibition in L driven down to cut-off

no signals are sent -> VOR not engaged and as head turns to R, eyes also drift to R

CNS has potential to recognize lost gaze and see corrective saccades

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15
Q

what is the effect on the inhibitory cut off if a virus attacking the peripheral vestib system resulting in a hypofunction at rest - describe specifically to a virus on L side

A

get asymmetry perceiving signals and CNS generates eye mvmt in response to perceived head mvmt

virus on L side -> tonic firing rate lower than normal -> asymmetry
- brain assumes head is turning to R when not
- see eyes move L and get spontaneous nystagmus R
- perceives head turning to be continuous so beaething occurs as trying to keep correcting i

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16
Q

what is a strategy to treat spontaneous nystagmus d/t unilateral vestib hypofunction from virus and when can this resolve

A

gaze fixation

occurs in absence of head mvmt and persists until CNS compensates for peripheral

17
Q

what is nystagmus, what are the types, and how is it named

A

involuntary rhythmic conjugate eye mvmt

spontaneous (no head mvmt)
gaze-evoked (end ranges)
positional (ie BPPV)

named for fast phase

18
Q

peripheral vs central nystagmus: location of lesion, presentation, trigger

A

p = end organs or nerves

c = brainstem & central connection

19
Q

peripheral vs central nystagmus: plane

A

p = mixed plane
- torsional, combined w horizontal or vertical

c = pure persistent vertical, torsional, or horizontal

20
Q

peripheral vs central nystagmus: presentation

A

p = slow phase eye mvmt (VOR) in one direction and fast phase saccadic “reset” back towards primary position

c = pendular (oscillate at equal speeds)

21
Q

peripheral vs central nystagmus: trigger

A

p = perceived head mvmt

c = disruption of central VOR pathways which are consistent w directions of head mvmt

22
Q

peripheral vs central nystagmus: impact of gaze fixation

A

p = dec w fixation

c = doesn’t dec w fixation

23
Q

peripheral vs central nystagmus: impact of gaze direction

A

p = non-direction changing w gaze direction, will always beat away from affected side

c = usually direction changing toward gaze direction

24
Q

peripheral vs central nystagmus: duration of sx

A

p = spontaneous horizontal nystagmus usually resolves w/i 3-7 days once CNS compensates or peripheral path resolves/quiets down

c = spontaneous nystagmus typically chronic and may not resolve

25
Q

what are the slow vs fast phases of nystagmus

A

slow = VOR
fast = saccadic reset

26
Q

what is central adaptation secondary to peripheral vestib dysfunction

A

CNS recognizes peripheral issue and adapts via compensatory mechanisms
- not dependent on therapy, resolves spontaneously

27
Q

how long can it take for central adaptation secondary to peripheral vestib dysfunction

A

up to 72hrs

28
Q

how is the CNS able to compensate for peripheral vestib dysfunction

A

utilizes other sensory inputs as reference point
- inc somatosensory and visual input

likely changes in levels in vestib nuclei to give input to rebalance cerebellum

29
Q

what is a consideration about components contributing to VOR function

A

secondary reflexes contribute to VOR

30
Q

vertigo = sx or dx

A

sx

31
Q

what is vertigo and how is it often described

A

illusory sensation of motion
rotational, translational, tilting of self/environment

“room spinning”

32
Q

what is dizziness and sx, and what can it be attributed to

A

nonspecific term that describes altered orientaiton in space

sx: lightheadedness, flainting, floating, waving, imbalance

vestib, CV, cerebrovascular, metabolic, meds

33
Q

what is dysequilibrium and what can it be associated with

A

inability to maintain upright posture -> can result in phenomenon known as lateropulsion or retropulsion

can be associated w non-vestib problems/CNS such as dec somatosensation or weakness

34
Q

what are 9 common vestib disorders /conditions

A

BPPV**
peripheral vestib hypo uni**
vestib loss (B)
meniere’s dz
central vestib disorders
head trauma
cervicogenic dizziness
migranous vertigo
vertebro basilar insufficiency