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phototransduction (1).docx

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McMaster University
Gautam Ullal

October 3 , 2012 Psych 2E03: Sensory Processes Phototransduction (1) Retina – The two major layers - photo-insensitive (pigment layer/retinal pigment epithelium) - photo-sensitive - functions of pigment layer:  reduce scattering of light  store vitamin A (retinol) for Rhodopsin synthesis  scavange debris and metabolic wastes - note: pigment layer is vital for the survival of photo-sensitive layer of retina - retinal detachment: separation of photo-sensitive lauer from pigment layer leads to acute blindness Retinal detachment - photosensitive layer separates from the pigment layer Photosensitive retina - bipolar layer: some neurons which have two processes in the cell body - some neurons may be multipolar: ganglion cells Photosensitive layer - light penetrates innermost layer to attain the outer layers (rods and cones) Convergence of rods and cones - high convergence: several cones/rods synapse with bipolar, several bipolar converge with retinal ganglion cells - low convergence in cone-fed circuits: 1:1:1 ratio - 160 million rods, 6 million cones, 1 million ganglion cells - cones are selective, they can tell apart two separate dots - rods give you a sense of light but are not as sharp - four tpes of photoreceptors and bout  twenty types of bipolar cells  twenty types of horizontal cells  fifty types of horizontal cells  twenty types of ganglion cells - types vary in terms of their properties such as thresholds or chemical processes Distribution of rods & cones - fovea cones only - as we move away rods Photoreceptors of retina - bipolar cells at synapse - rods: disks stacked have photosensitive pigments - cones: folded, pleats contain pigments Rod & Cone pigments - rod: rhodopsin - cone
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