Eye movement 2

Question 1

VORs
driven by?
what is the reflex

Answer 1

driven by vestib input from semicircular canals

center of gaze maintained by contraction of extraocular muscles so eyeball rotation opposes head rotation (conjugate because eyes move same amount)

Question 2

rightward head rotation signaled by___

left eye rotation produced by

Answer 2

right head = horiz canals

left eye =
1) excitation of motor neurons to left lateral rectus in left abducens

2) excitation of medial rectus by motor neurons in right oculomotor nucleus

Question 3

pathway of VOR horizontal gaze

Answer 3

1) had rotate to right, fluid in horiz canal lags so deflects cupula in both horiz canals
in right, depol hair cells
in left, hyperpol hair cells

2) excitation in right transmit to right vestib nuclei
then project via MLF to left lateral rectus neurons in abducens

3) any stim excite abducens neuron also excite internuclear interneurons which cross over and ascend in MLF to excite right medial rectus
4) coactivate left lateral rectus and right medial rectus

Question 4

where do interneurons for VOr horiz gaze cross over

Answer 4

at abducens nucleus

Question 5

simplified explanation of VOR

Answer 5

CN3 innerv R medial rectus

CN6 in caudal pons contract L lateral rectus
half of CN6 connect to CN 3

head to right excite vestib hair cells
axons contact lateral rectus motor neurons/interneurons to medial rectus
MLF runs from CN3 to cervical cord

Question 6

describe internuclear ophthalmoplegia

Answer 6

MLF damage –> disconnection of coord of medial and lateral recti during horizontal gaze

in MS

Question 7

describe what you observe for patient with INO

Answer 7

often get double vision
when young, think tumors
when middle age, young adults, think MS
when older, think vascular lesions

Question 8

how can you tell if medial rectus motorneurons and/or nerve are intact in a patient with INO

Answer 8

do convergance tests

medial rectus and motor neurons can be normal even if muscle not function during horiz gaze

if bring pen to left and left eye moves but right eye stays = MLF damage = conjugate abnormality

if can’t do horiz gaze saccades or pursuit but can do convergance then likely INO

Question 9

What is nystagmus
if head turn right
if head turn

Answer 9

if head turns to right, eye counter to left

if head turn, eyes rotate slowly until limit of eye rotation reached then snap back to new fixation point

Question 10

graphical pattern of nystagmus

Answer 10

slow ramp opposite to head rotation then fast saccade to center of eye position

Question 11

direction of nystagmus =

Answer 11

direction of rapid saccade