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pathway for control of eye movement
- superior colliculus: inputs in voluntary control saccades (REMs to salient stimuli) and in coordinating movements of head in concert with this
- -pretectal nuclei participate in pupillary reflexes
retina and optic nerve are part of what?
"blind spot" - where aonx exits and blood vessels pass
area of highest visual acuity
retinala structure; outer layer.
- photoreceptors -rods (night vision)
- and cones (for daylight and colour, densest just around fovea)
retinal structure; middle layer
bipolar neurons; horizontal (more superficial) and amacrine (deeper). both perform laternal interactions, which enhance visual contrast
retinal structure; inner layer.
ganglion cells. light goes thru to outermost layer, hits photoreceptor cells
cone bipolar cells:
input from small # of cones for high visual acuity
rod bipolar cells:
input from several rods for convergence and increased sensitivity at low illumination
at outermost extreme:
- pigmented epithelium- phagocytic role for removing old photoreceptors
- functions is absent in retinosa pigmentosum, which can detach retina
- bipolar neurons and ganglions cells process signal
- -in fovea, 1 cone -> 1 bipolar cell --> 1 ganglion cell
neural processing; fovea have ...
neural processing, at periphery
- many rods --> 1 bipolar cell
- which acuity is decreased
neural processing, other cells
other cells in retina participate in signal processing
ganglion cell axons gather together ...
and exit at optic disk, become myelinated and form optic nerve
optic nerves from both eyes converge at...
optic chiasm: partial cross-over
images in nasal hemiretina
from both sides cross ovver (temporal stay ipsilateral); allows for complete cross-over of each visual field
Right visual field maps on...
L visual cortex
some optic tracts axons
- do not go LGN of thalamus, but travel to brachium of superior colliculus
what layer recives direct input from retina?
- 1st layer;
- other layers receive input from 1st or from somatic sensory (AL system) and auditory systems
- -sensory info fr. differ modlities is lined up in differ layers -->output to eye and neck muscles so that one can properly orient to stimulus
Lateral Geniculate Nucleus is a?
- a nucleus in thalamus, which projects to the primary visual cortex and serves visual perception
- -laminated (6 layers) with alternating input from ipslateral and contralateral retina
division between 2 important input systems:
- Magnocellular & Parvolcellular
- -project to distinct parts of primary visual cortex
Magnocellular inputs from...
from M ganglion cells wwith wide dendritic arbours (integrates visual input info from wide area for motion vision)
Parvocellular input from...
- from P cells (ganglionic cells with small dendritic arbours)
- -for discriminative aspects of visual form and colour
course anterior for a short distance in order to mvoe over the lateral ventricles
Brodman's Area 17
primary cortex, in columnar fissure
Layer 4 (Stripe of Gennari)
densest projection to primary visual cortex (like other sensory)
in visual system, 3 types of aggregates.
- ocular dominance columns, orientation columns, aggregates of colour-sensitive neurons (colour blobs)
- -neurons lined up with similar properties across diff layers
Why are higher-order areas surround area 17 (area 18 and 19) are distinguishable?
lacking of Stripe Gennari
Magnocellular system to the primary cortex to higher order areas for visual form in mtoion (includes medial temporal projection)
parvocellular system to primary cortical projections in 4CB to colour blobs to higher order areas
form visual pathway
parvocellular system to 4CB to region between blobs to higher order cortex and inferior temporal lobe
Two streams of projections outside visual system:
- ventral: features :what
- dorsal: spatial info: 'where"
deficits in the optic nerve
transection = monocular blindness
deficits in optic chiasm
- (eg. pituitary tumor)
- -transection --bitemporal visual field deficit
deficits in optic tract or LGN
transection: contrlateral visual field deficits (homonynous hemianopsis
deficits at optic radiations
- transection of meyer's loop only (temporal region --contralateral upper quadrant (quandranotopia
- complete transection --homonymous hemianopsia
deficit in primary visual cortex
- most common
- infarction - homonymous hemianopia with macular sparing (secondary greater cortical representation)
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