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Neuroscience I Test 3 > Visual System > Flashcards

Flashcards in Visual System Deck (24)
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how are lesions of the visual system described?

-in terms of their visual field deficits
-visual field deficits are described from the perspective o the pt's right or left


what are the four quadrants of the retina and what visual quadrants do they receive?

1. upper nasal visual quadrant--projects to lower temporal retinal quadrant
2. lower nasal visual quadrant--projects to upper temporal retinal quadrant
3. upper temporal visual quadrant--projects to lower nasal retinal quadrant
4. lower temporal visual quadrant--projects to upper nasal retinal quadreant


where do axons of the ganglion cells terminate?

-majority terminate in the lateral geniculate body
-rest terminate in the superior colliculus as part of the tectal and visual reflex pathways


rules of retinotopic projection

-fibers from the temporal hemiretina do not cross in the optic chasm
-fibers from the nasal hemiretina cross in the optic chimes

Rule of L's
-info from the lower hemiretina projects to:
1. lateral part of the lateral geniculate body
2. loop of meyer
3. lingual gyrus


homonymous visual fields

-refer to corresponding halves of visual fields such as the temporal field of one eye and the nasal field of other
-Left temporal and R Nasal
-R temporal and L Nasal


heteronymous visual fields

-refer to non corresponding visual fields
-temporal field in the L and temporal field in the R
-nasal field in the L and temporal field in the R



-blindness in one half of the visual field
**nasal hemianopsia of the L eye indicates a lesion of the temporal hemiretina of the L eye



-blindness of a quadrant of the visual field
-most common involves the upper nasal quadrant of one eye and the upper temporal quadrant of the other eye called superior quadrantanopia--homonymous condition


binasal hemianopsia

-cause: bilateral lesion of the lateral aspect of the optic chiasm
-results: heteronymous blindness in the nasal fields of each eye
-may also be unilateral due to atherosclerosis of ICA
-ex: if bilateral lesion of the lateral aspect of optic chasm, blindness in the R and L nasal visual fields


unilateral nasal hemianopsia

-cause: unilateral lesion of the lateral aspect of the optic chiasm
-results: nasal hemianopsia (blindness) of the ipsilateral eye
-ex: lesion of the lateral aspect of the L optic chiasm results in (right) nasal hemianopsia of the left eye
-blindness in the nasal field of the left eye


bitemporal hemianopsia

-cause: midline lesion of the medial portion of the optic chiasm
-one type is due to a pituitary tumor
-results: bitemporal hemianopsia (blindness)
-ex: so if lesion to the medial aspect of the optic chasm, then blindness occurs in the temporal fields of both eyes


contralateral homonymous hemianopsia

-cause: unilateral lesion of the lateral geniculate body, complete optic radiations, or visual cortex
-results: contralateral homonymous hemianopsia
-ex: left homonymous hemianopsia due to a lesion on the R visual pathway (ie. optic tract, lateral geniculate body, optic radiations)


contralateral superior quadrantanopia

-cause: unilateral lesions of the loop of Meyer
-possibly due to a tumor of infarction of the posterior temporal lobe
-results: homonymous deficit
-ex: left superior quadrantanopia--due to a lesion in the R loop of Meyer causing blindness in the L temporal visual field and R nasal visual field


incongruent contralateral homonymous hemianopsia with macular sparing

-cause: unilateral lesion of the visual cortex
-possibly due to obstruction of the posterior cerebral artery
-results: contralateral hemianopsia that is not symmetrical in both eyes and does not occur in the macula
-lesions of the visual cortex are incongruous while lesions of the LGB or optic radiations are congruous
-ex: left incongruent homonymous hemianopsia with macular sparing--due to a lesion with the R primary visual cortex
-causes blindness in the L half of each eye (L temporal field and R nasal field) leaving the macula spared--not symmetrical on each side


visual agnosia

-pts are unable to visually recognize objects or pictures
-may be due to bilateral damage in the visual assoc cortices secondary to anoxia


associative visual agnosia

-infarction of the L occipital lobe and posterior corpus callous secondary to occlusion of the PCA
-disconnects the language area from the visual assoc cortex
-pt cannot name or describe an object in the visual field, but they can recognize and demonstrate their use
-visual perception intact
-pts are usually alexic (unable to read) and writing ability may be affected (agraphia)



-once a visual field is processed in the primary and associative visual cortices, it may be correlated with memory
-bilateral lesions in the occipito-temporal regions may result in bizarre disturbance of fine visual discrimination and ability to recognize extremely familiar faces


light reflex

-pupillary compression assoc with a normal response to shining an exam light into the pt's eye is a PS mediated response that is processed thru the PRETECTUM

-shining a light in an eye results in ipsilateral constriction of the pupil-->direct light reflex
light into R eye-->R retina-->optic N-->optic tract-->brachium of superior colliculus-->superior colliculus-->pretectum-->Edinger Westphal Nucleus-->Oculomotor N-->Ciliary Ganglion-->pupillary constrictor M-->ipsilateral pupillary constriction

-unilateral stimulus will also normally elicit pupillary constriction of the contralateral eye--consensual pupillary reflex
light into R eye->R retina-->optic N-->optic tract-->brachium of superior colliculus-->superior colliculus-->pretectum-->posterior commissure-->Edinger Westphal Nucleus-->Oculomotor N-->Ciliary Ganglion-->pupillary constrictor M-->ipsilateral pupillary constriction


pupillary dilation response

-dec in the amount of light reaching retina results in bilateral reflex dilation of the pupils
-sympathetic response mediated by brainstem and upper SC

dec light-->retina-->optic N-->superior colliculus-->pretectum-->reticular formation-->lateral reticulospinal tract-->preganglionic sympathetic neurons-->superior cervical ganglion-->pupillary dilator Ms-->pupillary dilation



-cortically mediated visual response
-originates in frontal eye field of frontal lobe
-triad of accommodation: convergence of vision, pupillary constriction, thickening of lens


Argyll Robertson pupil

-result of syphilis infection
-pupils are unreactive to light but constrict during accommodation
-due to destruction of pretectum--important in light reflex but not accommodation
-accomodating but unreactive--Prostitute's Pupil


Holmes Adie Pupil

-benign condition
-may be due to lesion of ciliary ganglion
-may confused with Argyll Robertson b/c of similar rxn to light, but distinguished by different rxns to accomodation


voluntary movements of the eye

-controlled by frontal eye fields in the posterior portion of the middle frontal gyrus
-corticotectal fibers descend to superior colliculus which in turn influences the motor neurons of III, IV, and VI


convolutional movements of eye

-controlled by occipital eye fields in the visual assoc cortex
-fibers from the occipital cortex descend as corticotectal fibers to superior colliculus which influence the LMNs of III, IV, VI