visual system: overview of visual pathway
Post on 20-Dec-2015
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Visual System: Overview of Visual Pathway
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optic nerve
optic chiasm
optic tract
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optic nerve
optic chiasm
optic tract
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V1
lateral view medial view
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V1
lateral view medial view
calcarine sulcus
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Visual System: Eye
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Optics of eye
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1. Want to see over a huge range of light levels
2. Need a wide visual field
3. Want high resolution image
Vision Challenges
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photoreceptor
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neurotransmitter release
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Phototransduction cascade:
Several kinds of protein molecules change shape
Second messenger (cGMP) gets cleaved
Na+ channels close
Voltage inside photoreceptor goes more negative
Neurotransmitter release decreases
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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
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neurotransmitter release
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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
Not very sensitive – daytime only
NEVER saturate
Good acuity
Provide color vision (humans)
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ROD PROPERTIES
Very sensitive – dusk, night
Saturate in moderate-bright light
Poor acuity
No color vision
CONE PROPERTIES
Not very sensitive – daytime only
NEVER saturate
Good acuity
Provide color vision (humans)
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Distribution of photoreceptors across retinacr
oss-
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thro
ugh
oute
r se
gmen
ts o
f ro
ds &
con
es
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cone
midget ganglion cells
bipolar cells
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Retinal ganglion cells have center-surround receptive fields – why?
center
surround
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responsestimulus
time
OFF retinal ganglion cell: receptive field, stimuli, and responses
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Mach bands
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Cone photopigments, human
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cone
midget retinal ganglion cells
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green cone
ON midget retinal ganglion cell
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Retinal ganglioncell 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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green cone
OFF midget retinal ganglion cell
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Retinal ganglioncell 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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red cone
ON midget retinal ganglion cell
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Retinal ganglioncell 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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red cone
OFF midget retinal ganglion cell
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Retinal ganglioncell 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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blue-on retinal ganglion cell
blue cone
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Retinal ganglioncell 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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green & red cones
ON parasol retinal ganglion cell
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Retinal ganglioncell 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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green & red cones
OFF parasol retinal ganglion cell
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Retinal ganglioncell 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 ganglioncell 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
85%
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Subcortical Visual System: LGN
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left eye’svisual field
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right eye’svisual 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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input from contralateral eyeinput from ipsilateral eye
ON cells
OFF cells
Each LGN layer contains a unique cell population
??