Eyes

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The retina

- A single layer od light-sensitive receptor cells ( cones and rods)

- The overall function of the retina is to gather information anout the incoming light and relay it to the brain via the optic nerve

- The actual image is formed in the brain

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Rod cells

- Rod shaped outer segment

- Many rods converge into one neurone

- Visual acuity is low

- 120 million per retina

- Visual pigment - Rhodopsin

- Found evenly all over retina

- Sensitive to low light intensity

- Black and white vision in poor light

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Cone cells

- Cone-shaped outer segment

- Only a single cone per neurone at the centre of fovea

- Visual acuity is high

- Visual pigment - Iodopsin

- 7 million per retina

- Found all over retina, but more concentated towards fovea, the fovea itself consists of only cones

- Only functions in bright light

- Seeing colour and detail in bright light

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Differences

- The pigment in rod cells is more easily bleached (broken down) than the pigment in cones

- Retinal convergence: Many rod cells converge into one neurone, so they can all contribute to teh generator potential, making it more likely that the threshold will be reached, this is called summation  

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