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Visual System: Overview of Visual Pathway
optic nerve
optic chiasm
optic tract
optic nerve
optic chiasm
optic tract
V1
lateral view medial view
V1
lateral view medial view
calcarine sulcus
Visual System: Eye
Optics of eye
1. Want to see over a huge range of light levels
2. Need a wide visual field
3. Want high resolution image
Vision Challenges
photoreceptor
neurotransmitter release
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
Pencil-sharpening cascade
Phototransduction cascade, key points:
Massive amplification of signal
Slow
Output (transmitter release) is graded
neurotransmitter release
Phototransduction cascade, key points:
Massive amplification of signal
Slow
Output (transmitter release) is graded
Same in cones as in rods
CONE PROPERTIES
Not very sensitive – daytime only
NEVER saturate
Good acuity
Provide color vision (humans)
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)
Distribution of photoreceptors across retinacr
oss-
sect
ion
thro
ugh
oute
r se
gmen
ts o
f ro
ds &
con
es
cone
midget ganglion cells
bipolar cells
Retinal ganglion cells have center-surround receptive fields – why?
center
surround
responsestimulus
time
OFF retinal ganglion cell: receptive field, stimuli, and responses
Mach bands
Cone photopigments, human
cone
midget retinal ganglion cells
green cone
ON midget retinal ganglion cell
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
green cone
OFF midget retinal ganglion cell
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
red cone
ON midget retinal ganglion cell
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
red cone
OFF midget retinal ganglion cell
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
blue-on retinal ganglion cell
blue cone
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
green & red cones
ON parasol retinal ganglion cell
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
green & red cones
OFF parasol retinal ganglion cell
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
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%
Subcortical Visual System: LGN
left eye’svisual field
right eye’svisual field
binocular visual field
binocular visual field
binocular visual field
The visual system is a completely crossed system
visual field
visual field
macaque monkey LGN
section through LGN(macaque monkey)
retinotopic map in left LGN
visual field
input from contralateral eyeinput from ipsilateral eye
ON cells
OFF cells
Each LGN layer contains a unique cell population
??
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