Visual tracts Flashcards
where is the object of attention centered at within the retina
fovea centralis and macula lutea
in what area of the eye are photoreceptors absent
optic disc (medial to the macula)
what are the two zones of the visual fields
binocular zone (seen by both eyes) mono-ocular zone (seen by only R/L eye)
what is a retinal field
the location on the retina where an object in the visual field is projected
what is the optic disc
the region where retinal axons leave the eye as the optic nerve
how is the image formed on the retina oriented
inverted along lateral and vertical axis
does the nasal or temporal half of retinal axons decussate at the optic chiasm
nasal half decussates to contralateral optic tract
what fibers are found within each optic tract
fibers from ipsilateral temporal retina and contralateral nasal retina
what does partial decussation of retinal fibers facilitate
depth perception
where does the optic tract terminate
lateral geniculate nucleus (LGN)
what forms the dorsal and lateral borders of the lateral geniculate nucleus
outgoing optic radiations
what forms the ventral base of the LGN
incoming optic tract
what are the first and second layers of the LGN called
magnocellular layers
what are the 3rd-6th layers of the LGN called
parvocellular layers
which layers of the LGN receive inputs from rods
magnocellular layers
which layers of the LGN receive inputs from cones
parvocellular layers
which layers of the LGN have larger receptive fields and are sensitive to moving stimuli
magnocellular layers
which layers of the LGN have smaller receptive fields and are sensitive to color and stationary stimuli
parvocellular layers
which layers of the LGN have thicker, faster conducting axons
magnocellular layers
where do axons from the temporal retina terminate
layers 2, 3, 5 of the ipsilateral LGN
where do axons from the nasal retina terminate
layers 1, 4, 6 of the contralateral LGN
what is an optic radiation
bundle of myelinated extensions from secondary neurons of LGN
where does the optic radiation go
to the primary visual cortex (upper and lower banks of the calcarine sulcus AKA lingual gryrus and cuneus)
fibers from which quadrant of the visual field go to the cuneus
lower quadrant of contralateral hemifield (dorsomedial LGN)
fibers from which quadrant of the visual field go to the lingual gyrus
upper quadrant of contralateral hemifield (ventrolateral LGN)
what is the path of fibers conveying information from the macula and fovea
central LGN => caudal visual cortex (posterior occipital pole)
what is meyer’s loop
an arch into the temporal lobe by the axons carrying information from the superior part of the visual field
where does meyer’s loop terminate
below the calacarine sulcus
the left upper quadrant of the visual field would be represented in what area of the visual cortecx
right lower quadrant (opposite that of the visual field)
what brodmann’s area corresponds to the primary visual cortex
17
what brodmann areas make up the visual association cortex
areas 18 and 19
what function does the superior colliculus have in the visual system
directing eye movements
what function does the pretectal area have in the visual system
pupillary light reflex
pupillary constrictor muscles receive PNS innervation from what nuclei
edinger-westphal nucleus
pupillary constrictor muscles receive SNS innervation from what nuclei
superior cervical ganglion
where do preganglionic cholinergic motor neurons travel and synapse
travel w/ ipsilateral CN III
synapse in ciliary ganglion
where do postganglionic cholinergic motor neurons travel
send axons via short ciliary ns to ciliary ms. and pupillary constrictors
mydriasis and paralysis of accomodation are caused by a lesion of what structure
ipsilateral CN III
how will partial optic nerve damage present when testing pupillary reflex
shining light in eye ipsilateral to lesion => diminished constriction of both eyes
light in eye contralateral to lesion => normal reflex
how will total optic nerve damage present when testing pupillary reflex
neither direct or consensual reflex of affected eye
how will posterior midbrain damage present when testing pupillary reflex
weakened pupillary reflex bilaterally
how will partial CN III damage present when testing pupillary reflex
direct and consensual response lost ipsilaterally, present contralaterally
what is hemianopia
blindness in one-half of visual field
what is quadrantanopia
blindness in one quadrant of visual field
what is homonymous visual fields
conditions in which visual field loss is similar in both eyes
what is heteronymous visual fields
conditions in which eyes have non-overlapping field losses
what is macular sparing
visual field loss the preserves vision in the center of visual field
where would a deficit be expected if damage is anterior to optic chiasm
only ipsilateral eye
what kind of deficit would be expected if damage is at the optic chiasm
heteronymous deficit (non overlapping visual field loss)
what kind of deficit would be expected if damage is behind the optic chiasm
homonomyous deficit (overlapping visual field loss)
associative visual agnosia is caused by occlusion of what artery
PCA
what structures are infarcted in associative visual agnosia
left occipital lobe and posterior corpus callosum
what is associative visual agnosia
disconnection of language area from visual association cortex
how does associative visual agnosia present
pt cannot name or describe object in visual field, but can recognize and demonstate its use
compromised reading and writing
