The Retina

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The Retina
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Photoreceptor cells4 light sensitive
proteinsrods with 1 type3 types of cones, each
with a single type
Receptors for light detection
Receptor cells
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StargazingFinding your car in a dark parking
lotChoosing socks
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Visual Acuity

• 120,000,000 rods and 6,000,000 cones per retina
• 1,200,000 retinal ganglion cells axons
• 1051 convergence ratio
• Fovea cones only, 11 highest visual acuity but
  poor sensitivity

Counting fingers andReading the Writing on the
Wall
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Demonstrationof Blind Spot (diagram)
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Web-based color deficiency test
Trichromatic Theory of Color Vision
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Bleaching of photopigments
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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?
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Hubel and Weisel Experiments
Youtube
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Parallel Processing in the Cortex

• Motion sensitive
• Color and shape sensitive

Story of woman atstreet crossing
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Why so much emphasis on the Visual System?