Eye Movements

Question 1

what is the purpose of eye movements?

Answer 1

achieve and maintain fixation
move the fovea to a target position and keep it there

Question 2

what are the components of the gaze system?

Answer 2

oculomotor system (eyes moving in orbits) and head movement (orbits moving in space

Question 3

what is a saccade

Answer 3

rapidly shifting the fovea to a visual target in the periphery

Question 4

what is smooth pursuit

Answer 4

keep the image of a moving target on the fovea (need a target to follow)

Question 5

what is vergence

Answer 5

movement of the eyes toward or away from the midline to adjust for distance
normal disconjugate movement

Question 6

what is vestibulo-ocular

Answer 6

hold images still on the retina during quick head movements

Question 7

what is optokinetic

Answer 7

maintain fixation on new objects during steady head movement or moving visual stimuli (like watching light poles in a moving car)
saccades and smooth pursuit

Question 8

what is visual fixation

Answer 8

hold the eyes still during intent gaze, suppression of eye movement

Question 9

what is conjugate eye movement

Answer 9

both eyes move in the same direction at the same speed

Question 10

what muscles are involved with eye adduction

Answer 10

medial, superior, and inferior rectus

Question 11

what muscles are involved with eye abduction

Answer 11

lateral rectus, superior and inferior oblique

Question 12

what muscles are involved with eye depression

Answer 12

inferior rectus, superior oblique

Question 13

what muscles does each direction of the H test check

Answer 13

Question 14

what are the two passive forces that must be overcome to move the eye?

Answer 14

viscous force that opposes rapid movement and elastic force that restores the eye to a central position

Question 15

what is saccadic pulse

Answer 15

high frequency neural burst to overcome orbit viscosity; achieves movement

Question 16

what is saccadic step?

Answer 16

steady frequency neural activity to overcome tissue elasticity; maintains steady position

Question 17

what are the pathway steps for eye movement

Answer 17

cortical eye fields - planning
basal ganglia - modulation
brainstem nuclei - pulse and step generators
CN motor nuclei
CNs
extra ocular muscles

Question 18

why is the superior rectus subnuclei important?

Answer 18

the nuclei innervate the contralateral SR, so due to the fiber crossing a lesion of the nucleus would have a bilateral affect

Question 19

what is the medial longitudinal fasciculus

Answer 19

a myelinated fiber tract that interconnects the oculomotor, trochlear, and abducens nuclei

Question 20

what does the MLF do?

Answer 20

serves to facilitate eye movements and conveys info about head movement

Question 21

where does the MLF ascend to?

Answer 21

the interstitial nucleus of Cajal

Question 22

what does the paramedian pontinereticular formation do

Answer 22

processes cortical signals and generates a pulse command that projects to the abducens nucleus

Question 23

what are the two neurons that come from the abducens nucleus during horizontal saccades?

Answer 23

motor neuron to the lateral rectus
internuclear neuron to contralateral oculomotor nucleus via MLF

Question 24

horizontal saccades steps

Answer 24

control signals from frontal eye fields and superior colliculus synapse on the contralateral PPRF
from PPRF to ipsilateral abducens nucleus
motor neuron to LR and internuclear neuron to contralateral CN III nucleus via MLF
motor neuron to MR

Question 25

where are omnipause neurons located? what do they do?

Answer 25

in the nucleus of the dorsal raphe they prevent unwanted saccades by arresting them, providing stability to the system

Question 26

what must be inhibited to generate a saccade?

Answer 26

omnipause neurons

Question 27

what do burst neurons do?

Answer 27

excite inhibitory neurons that project to the contralateral PPRF and abducens nucleus (contralateral from where the signal was generated)

Question 28

what integrates the velocity signal to a tonic position?

Answer 28

medial vestibular nucleus, nucleus prepositus hypoglossi, flocculus of cerebellum

Question 29

what would cause the eyes to drift back to the middle position after a saccade?

Answer 29

lack of integration of the velocity signal to a tonic position signal

Question 30

where do the frontal eye fields project to for vertical saccades?

Answer 30

rostral interstitial nucleus of the MLF (riMLF) (pulse command) interstitial nucleus of Cajal (step command)

Question 31

what do vertical saccades require? where does this occur?

Answer 31

requires communication on both sides of the midbrain reticular formation which occurs via the posterior commissure

Question 32

vertical saccades elevation pathway

Answer 32

cerebral cortex and superior colliculus send signals to both irMLF and interstitial nucleus of Cajal both of these nuclei send signals to both ipsilateral and contralateral oculomotor nuclei to synapse on motor neurons for the contralateral SR and ipsilateral IO

Question 33

vertical saccades depression pathway

Answer 33

CC and SC send signals to irMLF and interstitial nucleus these nuclei send signals to the ipsilateral trochlear nucleus and contralateral oculomotor nucleus motor neurons then synapse on the contralateral IR and SO

Question 34

where do excitatory projections from the frontal eye field go to

Answer 34

descend to the superior colliculus, riMLF, and PPRF

Question 35

where do the frontal eye fields receive input from?

Answer 35

supplementary eye fields

Question 36

where does the posterior parietal cortex project to?

Answer 36

superior colliculus

Question 37

what is the superior colliculus? what does it do?

Answer 37

a major visuomotor integration region works to initiate eye movements toward stimuli

Question 38

what strongly inhibits the superior colliculus?

Answer 38

substantia nigra pars reticulata

Question 39

how is inhibition of the superior colliculus suppressed?

Answer 39

by the caudate nucleus, just before saccades

Question 40

where does the superior colliculus project to?

Answer 40

PPRF or riMLF

Question 41

what does smooth pursuit initiation?

Answer 41

frontal eye field

Question 42

what calculates the velocity of a moving target?

Answer 42

middle temporal and medial superior temporal areas

Question 43

oculomotor nerve palsy presentation

Answer 43

down and out eye position decreased tone in all but LR and SO impaired convergence ptosis

Question 44

trochlear nerve palsy presentation

Answer 44

impaired torsion and depression head tilts away from affected eye to compensate for hypertrophic and extorsion

Question 45

abducens nerve palsy presentation

Answer 45

impaired abduction of affected eye adduction of affected eye at rest