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46 Cards in this Set

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What range of velocity do FAST eye movements occur?
300 to 700 degrees per sec
What range of velocity do SLOW eye movements occur?
20 TO 50 DEG per sec
what are two examples of fFEM>?
- saccade
- quick phase of nystagmus
what are 4 examples of SEM?
- SMooth opursuit
- optokinetic eye moevement
- vestibular eye movement
- vergence eye movement
What is the purpose of eye movement
to maintain foveal fixation, a greater field of vision, and BSV
purpose of a saccade?
bring object onto fovea
purpose of nystagmus - quick phase
directs fovea toward oncoming visual scene - reset eyes during prolonged rotation
purpose of pursuit?
hold image of moving target on fovea
purpose of optokinetic movement
hold image steady on retina during sustained head rotation
purpose of vestibular movent
holds images steady during brief head movements
purpose of vergence
holds image of single object on both foveas
what are the four supranuclear eye movement systems
saccades, pursuit, vergence and vestibular eye movements
WHAT are saccades? what do they serve as a mechanism for?
fast simultaneous movement of both eyes in same direction
fixation, refixation, rapid eye movements, fast phase nystagmus
What area of the frontal cortex are saccades produced????????????
Brodmann's area 8
True/False - Humans and animals look at scenes in a steady way
False - small parts of a scene are sensed so that greater resolution is achieved
What is defined as the amplitude of a saccade?
angular distance that the eye needs to move during the movement
What is saccade latency?
defined as the delay encountered between presentation of a stimulus and onset of saccade
normal ~ 200 ms
Why do our eyes continuously microsaccade?
since rods and cones only respond to changes in luminance - continuous microsaccades maintain the vision (without them the vision would cease)
What is nystagmus?
rhythmic back and forth movement of eyes - fast in one direction (involuntary saccade) and slow in other (pursuit)
Describe the pathway for saccades
origin: brodmann area 8
descends as frontomesencephalic tract to the midbrain, splits: vertical gaze and horizontal gaze

horizontal: cross on level of CN IV and descend on opposite side to HGC near abducens nucleus (PPRF)

vertical: fibers end on same side in the posterior commisure (up) or riMLF (down)
hat are the three type of cells associated with saccadic movement
burst cells
pause cells
tonic cells
what do burst cells do?
burst cells fire just before and during a SAccade
what do pause cells do
they are on all the time except during a saccade -
what do tonic cells do?
discharge in relation to eye position - hold it in position
what structure controls and calibrates saccades and other eye movements?
cerebellum
true or false - we have no control over all saccadic speed
true
which eye movement system exists to assist the vestibular reflex?
pursuit
which pathway crosses, saccadic or pursiot
saccade
what happens in smooth pursuit when the moving target starts moving too quickly?
saccades instead of pursuit to continue tracking
where are the origin centers for the pursuit system>
brodmann areas 19, 37, 39
(junction of occipital, parietal and temporal lobes)
describe the pathway for pursuit system
origin at junction of brodmann areas 19, 37 and 39
follows occipitomesencephalic tract to midbrain
splits: horizontal gaze and vertical gaze

vertical: go to post commisure (down) and riMLF (up); they mix with vertical saccadic fibers and travel to the PPRF
do the fibers from the pursuit system decussate?
either double decussation or none at all such that fibers remain ipsilateral
left occipital lobe controls what?
left gaze (pursuit)
what percent of te macula is necessary for fixation
50%
what can a parietal lobe lesion cause
since pursuit system initiated at junction of parietal, occipital and temporal lobes, this will cause abnormality in pursuit system to the ipsilateral side
cogwheeling
what can an occipital lobe lesion cause
cause homonymous hemianopia
(normal pursuits even with field defect suggest occipital lobe lesion)
What would be the indication if the OKN response in a patient was asymmetrical or absent?
pathological condition - abnormal connexions from visual cortex to ocular motor system
What are two stimuli for disjugate eye moevem,nts?
retinal blur
disparity

BSV is maintained by converging or diverging
which is the slowest eye monement?
vergence
describe vergence pathway
origin at brodmann area 19
travels to pretectal area and midbrain tegmentum
What organs control the vestibular eye movements>
inner ear organs labyrinth and otolith
what is endolymph?
gel contained in semicircular canals, utricle and saccule
used to control eye movement upon head movement
Where is the vestibular nucleus located?
below CN VI nuc
What are the 3 types of canals in the ear? what do they influence?
horizontal canals: ipsilateral MR and contralateral LR
posterior canals: down/torsion ipsi SO contra IR
anterior canals: up/torsion ipsi SR, contra IO
What happens when cold water is splashed into pt's ear (only one)?
nystagmus with fast phase toward opposite side
{COWS}
What happens when you splash bilaterally pts ears with cold water?
(CUWDS)
upbeat nystagmus