receptors in the eye

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  • receptors in the eye
    • found in the innermost layer: the retina
    • Rod Cells
      • cannot distinguish between different wavelngths
        • can only see in back and white
          • There are more Rod cells and cone cells in the eye
      • many rod cells are attached to one neurone
        • so can respond to light of very low intensities
          • a threshold must be overcome to produce a generator potential
            • more likely to overcome the threshold as many rod cells are attached to one bipolar cell
    • Cone Cells
      • There are three different wavelengths of light
        • depending on the proportion of each type that is stimulated
          • so we can perceive images in full colour
      • there are 6 million cone cells
        • each has its own bipolar cell
          • cone cells only respond to high light intensity
            • The pigment idopsin requires a higher light intensity
              • cannot see at night
                • the brain can distinguish between the two separate impulses
                  • two dots together will appear as two dots
                    • has high visual acuity
    • to create a generator potential the pigment rhodopsin must be broken down
      • low intensity light is needed to cause the breakdown
        • many rod cells to one bipolar cell will only generate one impulse
          • no matter how many neurones are stimulated
            • they cannot distinguish between the sources of light that stimulated them
              • two dots together will appear as a single blob
                • rod cells have low visual acuity
                  • at the peripheries of the retina only rod cells are found
    • distribution of rod and cone cells on the retina is uneven
      • fovea has the highest intesnsity of light
        • by having different types of light receptors, each reponding to differnt stimuli, mammals can benefit from good vision in night and day

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