1. The Visual System Part 2

2. The Retina

3. S 15
Receptors for
light detection
Photoreceptor cells 4 light sensitive proteins: rods with 1 type 3 types of cones, each with a single type
Receptor cells

4. 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

7. Trichromatic Theory of Color Vision
“Blue” cones
“Green” cones
“Red” cones
Web-based color deficiency test
Trichromatic Theory of Color Vision

8. “Bleaching” of photopigments

9. What is the advantage of this multistep process?
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?

10. Hubel and Weisel Experiments
Youtube

12. Parallel Processing in the Cortex
Motion sensitive
Color and shape sensitive

13. Why so much emphasis on the Visual System?