Visual Tracts Flashcards
What is the difference btw the visual field and the retinal field?
Visual field = area that persion is able to see when eyes are fixed
image on retina = retinal field
Where is the blind spot?
where optic disc is = no photoreceptors here
What are the fovea centralis and macula lutea?
object of attention = fovea centralis
macula lutea is surrounding 1 cm
What are the subdivisions of the visual field?
binocular zone: central region seen by both eyes
Monocular zone: edges, seen only by one eye
What are the subdivisions of the retinal fields?
nasal and temporal hemifields
upper and lower quadrants
which parts of the optic nerve decussate in the optic chiasm?
nasal half of each retina –> goes to contra optic tract
temporal half of each retina –> ipsi optic tract
What is the purpose of partial decussation of the optic nerves?
creates depth perception
Where does the optic tract synapse?
curves posteriorly around cerebral peduncle –> terminates in lateral geniculate nucleus (LGN)
in precise retinotopic pattern
What forms the ventral and dorsal borders of the LGN?
ventral = optic tract fibers
dorsal and lateral borders = outgoing optic radiations
What are the magnocellular layers of the LGN?
layers 1 and 2 (dorsal)
large cells
receive ganglion cell inputs relayed from rods
What are the parvocellular layers of the LGN?
layers 3-6 (dorsal)
small cells
receive input from cones
Where do temporal retinal fibers terminate?
remain uncrossed –> terminate in layers 2,3, and 5 of ipsi LGN
Where do nasal retinal fibers terminate?
cross –> contra layers 1, 4, and 6 of LGN
How many times is the same point in the visual field represented?
6 times
once in each layer of the LGN
bc optic tract axons branch in multiple layers even though they’re from the same visual field
What is the optic radiation?
secondary neurons from LGN –> to primary visual cortex in calcarine sulcus
myelinated
retinotopic organization is maintained, but ind fibers carry info from one eye
Where is the primary visual cortex?
upper and lower banks of the calcarine sulcus
How are optic radiations divided?
- from lower quadrant of contra hemifield –> thru retrolenticular limb of internal capule –> to superior bank of calcarine sulcus = cuneus
- from upper quad of contra hemifield –> pass thru temporal lobe –> inferior bank of calcarine sulcus = lingual gyrus
- from macula and fovia –> pass to caudal parts of visual cortex
why can temporal lobe damage cause superior visual field deficit?
bc fibers from contra upper quad pass thru temporal lobe on way to visual cortex = meyer loop
How is macula represented in the LGN and visual cortex?
in disporportionately large volumes
most posteriorly in region of occipital pole
What is Brodmann’s area 17?
the primary visual cortex
Why is the primary visual cortex called the striate cortex?
bc you can see numerous myelinated fibers w/in a discrete layer –> striped appearance
What surrounds the striate cortex and what does it do?
areas 18 and 19
this + related parts of temporal and parietal lobes = visual association cortex
parieto-occipito-temporal area
helps interpret location, motion, form color
What does the superior colliculus do in vision?
spatially directs head movements and visual reflexes
retinal input –> bypasses LGN –> brachium of superior colliculus
cortical input: from area 17 –> brachium –> superior colliculus
What does the pretectal area do in vision?
bilateral grp of interconnected nuclei near midbrain/forebrain jxn
input from afferent bilateral fibers from optic tract; LGN and suprachiasmatic nucleus
respond to varying intensities of light –> mediate pupillary light reflex
