the visual system part 2. the retina photoreceptor cells 4 light sensitive proteins: rods with 1...
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Photoreceptor cells
4 light sensitive proteins:rods with 1 type3 types of cones, each with a single type
Receptors for light detection
Receptor cells
S 15More membrane =
more photosensitive molecules =more sensitive to light
Visual Acuity• 120,000,000 rods and
6,000,000 cones per retina
• 1,200,000 retinal ganglion cells & axons
• 105:1 convergence ratio
• Fovea: cones only, 1:1 highest visual acuity but poor sensitivity
Counting fingers andReading the Writing on the Wall
•Differences in spectral sensitivity due to 4 types of opsin. Rods have 1 type; Each type of cone has another type.
Trichromatic Theory of Color Vision
Web-based color deficiency test
“Blue” cones “Green” cones “Red” cones
The cascade of events initiated by light in a photoreceptor. The result of the cascade is to close a cGMP-gated sodium channel, reducing the inward current and hyperpolarizing the membrane. Source: Kandel, Schwartz & Jessell, Principles of Neural Science, 4th Edn
What is the advantage of this multistep process?
Hubel and Weisel Experiments
RetinalGanglionCells
LateralGeniculateNeurons
VisualCortexNeurons
Youtube
Parallel Processing in the Cortex
• Motion sensitive
• Color and shape sensitive
Story of woman atstreet crossing