Visual System: Overview of Visual Pathway.

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Presentation transcript:

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 retina cross-section through outer segments of rods & cones

cone midget ganglion cells bipolar cells

Retinal ganglion cells have center-surround receptive fields – why? center surround

response stimulus 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 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

green cone OFF midget retinal ganglion cell

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

red cone ON midget retinal ganglion cell

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

red cone OFF midget retinal ganglion cell

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

blue-on retinal ganglion cell blue cone

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

green & red cones ON parasol retinal ganglion cell

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

green & red cones OFF parasol retinal ganglion cell

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

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 85%

Subcortical Visual System: LGN

left eye’s visual field

right eye’s visual field

binocular visual field

The visual system is a completely crossed system

visual field

macaque monkey LGN section through LGN (macaque monkey)

retinotopic map in left LGN visual field

input from contralateral eye input from ipsilateral eye ON cells OFF cells Each LGN layer contains a unique cell population ??