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Motility > Ch15-16 VOR-OKN Systems > Flashcards

Ch15-16 VOR-OKN Systems Flashcards

1
Q

What is the VOR?

A

Vestibulo-Ocular reflex. It is the most primitive eye movement system which is elicited by activities with the vestibular apparatus

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2
Q

What does the Vestibular system do to eye movements?

A

it generated rapid and efficient eye movements to compensate brief and transient head movements

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3
Q

How fast does retinal image motion have to be to have significant acuity loss?

A

3-5 deg/sec

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4
Q

what are the 2 oculomotor systems that keep our retinal images steady?

A

The vestibular system and the optokinetic system

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5
Q

What is TVOR?

A

Transitional vestibulo-oculo reflex happens due to otholiths.
“ move me from here to here”

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6
Q

what is OKAN

A

Optokinetic after nystagmus.

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7
Q

How is OKAN measured?

A

in the ark, follows a period of OKN stimulation

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8
Q

How is gain measured?

A

Eye velocity/ Head velocity

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9
Q

How is VOR phase calculated?

A

measure of synchrony between head and eye velocity ( the relative position of eyes and head must be matched, the phase lag is almost at zero for undamaged)

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10
Q

VElocity step stimulus

A

sudden acceleration to a constant velocity rtation

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11
Q

Prerotational response

A

nystagmus induced by onset of a velocity step stimulus

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12
Q

post rotational response

A

nystagmus induced by offset and sudden cessation of a velocity step rotation.

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13
Q

velocity storage

A

central vestibular mechanism where by the peripheral layrinthe response is prolonged and OKAN AND OKAAN are generated

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14
Q

time constant

A

time taken for the slow phase eye velocity to decline to 37% of its initial value after the onset of a velocity step stimulus.

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15
Q

ocular counter rolling

A

tortional rotation of the eyes induced by the tilting of the head towards the shoulder

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16
Q

circularvection

A

illusion of self rotation induced during OKN stimulation

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17
Q

vertigo

A

illusion of movement of self or environment

18
Q

oscillopsia

A

illusory to and fro movements of the environment

19
Q

what are the dimensions of the ampulla?

A

its the bulbous area of the SCC and it is 0.1 mm diameter and 10-15mm long

20
Q

where is the crista ampularis located?

A

in each duct of the SCC

21
Q

what is the dimensions of the crista ampularis?

A

1mm in diameter and it is stimulated by the rotation of the head

22
Q

what makes up the vestibular system?

A

the SCC, utricles and the saccules this lies superiorly in the inner ear

23
Q

where is the cochlea located?

A

auditory system, inferiorly in the inner ear

24
Q

what is the perilymph?

A

occupies the adjourning space between the petrous and membranous labyrinths.brings nutrients if this gets in SCC can cause infections

25
Q

At what angle do horizontal canals lie adn what do they respond to?

A

25% to the earth’s horizontal plane and responds to horizontal rotational stimulus

26
Q

what angle do vertical canals lie adn what do they respond to?

A

45 deg. in respect to the sagittal plane the posterior and anterior are parallel

27
Q

how do the lateral SCC lie?

A

30 degrees with the objective horizontal meridian when the head is in normal erect position.

28
Q

What does the vestibular system maintain?

A

equilibrium
directing gaze
preserve constant plane of vision

29
Q

What is the mechanical response of SCC?

A

hydrodynamic. endolymph moves and cupula senses it

30
Q

What is the cristae ampullaris most sensitive to?

A

brief head turns

31
Q

what is the hair cell made up of?

A

1 kinocilium and 70 sterocilia arranged in decreasing length from kinocilium

32
Q

how is the polorization of hair cells calculated?

A

towards the kinocilium = depolarize

away= hyperpolorize

33
Q

what is the time constant for the restoration of the cupula?

A

6 secs

34
Q

how is the ampullofugal flow paired in both ears?

A

right anterior is accompanied by ampullopetal flow in left posterior scc. right lat- scc is accompanied by left scc

35
Q

how is VOR gain with sinusoidal inputs calculated?

A

peak slow phase eye velocity/ peak head velocity

36
Q

what is normal VOR gain?

A

1.0 w/ phase difference of 180 degrees aka zero phase shift

37
Q

at what frequency does VOR decline?

A

5 Hz and 10 HZ

38
Q

how is gain of sustained rotations calculated?

A

initial eye velocity/ head velocity

39
Q

after how long does slow phase velocity decline to 0

A

30 secs (time it takes to decrease to 37%

40
Q

what happens to a large time constant?

A

the less phase shift that happens at a given frequency and the better the compensation

Motility (6 decks)

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