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46 Cards in this Set
- Front
- Back
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What range of velocity do FAST eye movements occur?
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300 to 700 degrees per sec
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What range of velocity do SLOW eye movements occur?
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20 TO 50 DEG per sec
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what are two examples of fFEM>?
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- saccade
- quick phase of nystagmus |
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what are 4 examples of SEM?
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- SMooth opursuit
- optokinetic eye moevement - vestibular eye movement - vergence eye movement |
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What is the purpose of eye movement
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to maintain foveal fixation, a greater field of vision, and BSV
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purpose of a saccade?
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bring object onto fovea
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purpose of nystagmus - quick phase
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directs fovea toward oncoming visual scene - reset eyes during prolonged rotation
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purpose of pursuit?
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hold image of moving target on fovea
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purpose of optokinetic movement
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hold image steady on retina during sustained head rotation
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purpose of vestibular movent
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holds images steady during brief head movements
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purpose of vergence
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holds image of single object on both foveas
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what are the four supranuclear eye movement systems
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saccades, pursuit, vergence and vestibular eye movements
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WHAT are saccades? what do they serve as a mechanism for?
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fast simultaneous movement of both eyes in same direction
fixation, refixation, rapid eye movements, fast phase nystagmus |
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What area of the frontal cortex are saccades produced????????????
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Brodmann's area 8
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True/False - Humans and animals look at scenes in a steady way
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False - small parts of a scene are sensed so that greater resolution is achieved
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What is defined as the amplitude of a saccade?
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angular distance that the eye needs to move during the movement
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What is saccade latency?
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defined as the delay encountered between presentation of a stimulus and onset of saccade
normal ~ 200 ms |
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Why do our eyes continuously microsaccade?
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since rods and cones only respond to changes in luminance - continuous microsaccades maintain the vision (without them the vision would cease)
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What is nystagmus?
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rhythmic back and forth movement of eyes - fast in one direction (involuntary saccade) and slow in other (pursuit)
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Describe the pathway for saccades
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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) |
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hat are the three type of cells associated with saccadic movement
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burst cells
pause cells tonic cells |
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what do burst cells do?
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burst cells fire just before and during a SAccade
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what do pause cells do
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they are on all the time except during a saccade -
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what do tonic cells do?
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discharge in relation to eye position - hold it in position
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what structure controls and calibrates saccades and other eye movements?
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cerebellum
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true or false - we have no control over all saccadic speed
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true
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which eye movement system exists to assist the vestibular reflex?
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pursuit
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which pathway crosses, saccadic or pursiot
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saccade
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what happens in smooth pursuit when the moving target starts moving too quickly?
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saccades instead of pursuit to continue tracking
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where are the origin centers for the pursuit system>
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brodmann areas 19, 37, 39
(junction of occipital, parietal and temporal lobes) |
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describe the pathway for pursuit system
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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 |
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do the fibers from the pursuit system decussate?
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either double decussation or none at all such that fibers remain ipsilateral
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left occipital lobe controls what?
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left gaze (pursuit)
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what percent of te macula is necessary for fixation
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50%
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what can a parietal lobe lesion cause
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since pursuit system initiated at junction of parietal, occipital and temporal lobes, this will cause abnormality in pursuit system to the ipsilateral side
cogwheeling |
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what can an occipital lobe lesion cause
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cause homonymous hemianopia
(normal pursuits even with field defect suggest occipital lobe lesion) |
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What would be the indication if the OKN response in a patient was asymmetrical or absent?
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pathological condition - abnormal connexions from visual cortex to ocular motor system
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What are two stimuli for disjugate eye moevem,nts?
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retinal blur
disparity BSV is maintained by converging or diverging |
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which is the slowest eye monement?
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vergence
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describe vergence pathway
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origin at brodmann area 19
travels to pretectal area and midbrain tegmentum |
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What organs control the vestibular eye movements>
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inner ear organs labyrinth and otolith
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what is endolymph?
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gel contained in semicircular canals, utricle and saccule
used to control eye movement upon head movement |
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Where is the vestibular nucleus located?
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below CN VI nuc
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What are the 3 types of canals in the ear? what do they influence?
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horizontal canals: ipsilateral MR and contralateral LR
posterior canals: down/torsion ipsi SO contra IR anterior canals: up/torsion ipsi SR, contra IO |
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What happens when cold water is splashed into pt's ear (only one)?
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nystagmus with fast phase toward opposite side
{COWS} |
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What happens when you splash bilaterally pts ears with cold water?
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(CUWDS)
upbeat nystagmus |
