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The Visual System Part 2

The Visual System Part 2. The Retina. S 15. More membrane = more photosensitive molecules = more sensitive to light. Photoreceptor cells 4 light sensitive proteins: rods with 1 type 3 types of cones, each with a single type. Receptors for light detection. Receptor cells.

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The Visual System Part 2

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  1. The Visual SystemPart 2

  2. The Retina

  3. S 15 More membrane =more photosensitive molecules =more sensitive to light Photoreceptor cells4 light sensitive proteins:rods with 1 type3 types of cones, each with a single type Receptors for light detection Receptor cells

  4. StargazingFinding your car in a dark parking lotChoosing socks

  5. 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

  6. Demonstrationof Blind Spot (diagram)

  7. Differences in spectral sensitivity due to 4 types of opsin. Rods have 1 type; Each type of cone has another type. “Green” cones “Blue” cones “Red” cones Web-based color deficiency test Trichromatic Theory of Color Vision

  8. “Bleaching” of photopigments

  9. 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 VisualCortexNeurons LateralGeniculateNeurons Youtube RetinalGanglionCells

  11. Parallel Processing in the Cortex • Motion sensitive • Color and shape sensitive Story of woman atstreet crossing

  12. Why so much emphasis on the Visual System?

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