Visual Pathway

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Visual Pathway
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V1
calcarine sulcus
medial view
lateral view
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Visual System Eye
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Vision Challenges

• Want to see over a huge range of light levels
• Need a wide visual field
• Want high resolution image

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rhodopsin
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Phototransduction cascade Several different
protein molecules Second messenger (cGMP)
Closing of Na channels Change in voltage
inside rod Change in neurotransmitter release
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Pencil-sharpening cascade
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Phototransduction cascade, key points Massive
amplification of signal Slow Output
(transmitter release) is graded Same in cones
as in rods
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CONE PROPERTIES
ROD PROPERTIES
Not very sensitive daytime only NEVER
saturate Good acuity Provide color vision
(humans)
Very sensitive dusk, night Saturate in
moderate-bright light Poor acuity No color
vision
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Distribution of photoreceptors across retina
cross-section through outer segments of rods
cones
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cone
bipolar cells
midget ganglion cells
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Retinal ganglion cells have center-surround
receptive fields why?
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response
stimulus
time
OFF retinal ganglion cell receptive field,
stimuli, and responses
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Cone photopigments, human
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midget ganglion cells
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Retinal ganglion cell receptive fields
green on-center green off-center red
on-center red off-center
blue on-center black white on-center black
white off-center
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midget ganglion cells
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Retinal ganglion cell receptive fields
green on-center green off-center red
on-center red off-center
blue on-center black white on-center black
white off-center
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Retinal ganglion cell receptive fields
green on-center green off-center red
on-center red off-center
blue on-center black white on-center black
white off-center
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Retinal ganglion cell receptive fields
green on-center green off-center red
on-center red off-center
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blue on-center black white on-center black
white off-center
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Subcortical Visual System LGN
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left eyes visual field
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right eyes visual field
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binocular visual field
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binocular visual field
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binocular visual field
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The visual system is a completely crossed system
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visual field
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visual field
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macaque monkey LGN
section through LGN (macaque monkey)
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retinotopic map in left LGN
visual field
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macaque monkey LGN
section through LGN (macaque monkey)
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Each LGN layer contains a unique cell population
input from contralateral eye input from
ipsilateral eye
??
ON cells
OFF cells