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NESC 2570 (6)

March 20th 2012.docx

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NESC 2570
Stefan Kreuger

March 20th 2012 April-11-12 9:39 AM Structure of the retina  Light enters the eye, and travels to the back of the eye where the rods and cones are located  Rods and cones transduce using the same transduction scheme o But they are both sensitive to different wavelengths  Most eye diseases result from problems in the photoreceptors o Since they are very metabolically active cells  The other classes of eye diseases result from damaged ganglion cells o Usually just from natural cell death Transduction occurs in photoreceptors  Melenopsin ganglion cells can transduce a little bit too o React to blue light, and depolarize very slowly o They are responsible for triggering circadian rhythms, they don't produce actual "vision" o Persist longer in damaged retina than other ganglion cells *Light flash causes hyperpolarization, NOT depolarization  So dark is the "stimulus" for photoreceptors Rod outer segments  In dark: o Have light sensitive molecule Rhodopsin  Signal to cyclic nucleotide gated channels (CNG channels)  Non-selective cation channels  Sodium and calcium go in  Potassium goes out  Since the channels are non-selective, tend to depolarize the membrane toward 0mV  There are also voltage gated potassium channels  Bring the rods back to resting potential o Resting potential is -40mV o In light, membrane potential goes to -50 to -60mV  Calcium influx is important o It plays a role in adaption o Volta
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