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Vis Reflexes

Visual Reflexes & Eye Movements

Direct Light Reflex Afferents Retina, CN 2, optic tract > Superior Colliculus > Interneurons > E-W nucleus
Direct Light Reflex Efferents E-W nucleus via CN 3 > ciliary ganglion & sphincter mm of eye
Problems with Light Reflex Damaged retina/CN 2- if complete blindness, loss of both direct & consensual reflex when light shown in damaged eye; No problems w/ reflex w/ damaged LGN, optic radiations, visual cortex of 1 side or cortical blindness
When object close to face Convergence Pupillary constriction Near rxn Accomodation
Accommodation Afferent Limb Optic n, chiasm, & tract; LGN & optic radiation to visual cortex; Visual cortex connected to frontal EF; From EF, fibers descend through IC to CN 3; From EF, other cortical fibers synapse w/ PNS fibers (E-W nuc) Causes pupil constriction
Adie's Tonic Pupil Lesion of PNS ciliary ganglion/nerves; Benign unilateral dilated pupil; Decreased/no light reflex; slow contraction to near vision; slow dilation in dark
Argyll Robertson Pupil Small, irregular pupil no reaction to light; Does react to accommodation; Interruption of fibers running from pre-tectal nucleus to E-W nucleus
Marcus Gunn Paradoxical dilation both pupils that occurs when light shown in symptomatic eye AFTER shown in normal eye
Saccadeic Sub-system Places fovea on target rapidly & accurately--fixation
Saccadic Sub-systems Volitional; Reflexive; Volitional visually guided: actively look & find object (something particular); Reflexive visually guided: combination w/ pursuit; someone says ball is coming & you look at it
Lesions to Saccadic Pathway Hypometria- saccades too small; Dysmetria- too slow & inaccurate Saccadic palsy- delayed onset/no saccadic activity
How to test saccades Have pt look b/t 2 wide-set objects
Pursuit mvmts Fixation on slowly moving objects; if it fails, saccades must catch up
Lesion of Pursuit Movements Movement of object off fovea > saccade, no pursuit > series of small saccades to follow target
Vestibulo-Ocular Reflex Prevents image from moving off fovea
Vestibulo-Ocular Afferent Hair cells in semi-circular canals to ipsilateral vestibular nuclei
Vestibulo-Ocular Efferent Vestibular nuclei to extraocular mm.
How would you test for vestibulo-ocular reflex? Doll's Eye
Otokinetic Sub-system Eye mvmts in reponse to retinal slip during head mvmt at constant velocity; Direct path: retina, optic tract nuclei- cblm/vestibular nuclei
Created by: 1190550002