Vision- Signal Transduction-What is Light?-How does light get to the photoreceptors?Slide 4RetinaFoveaHow are images projected onto the retina?Slide 8Slide 9Slide 10“Dark Current”Slide 12Slide 13In dim light, which type of photoreceptor is more depolarized?SummaryVision- Signal Transduction•How does the eye detect light and transduce light into a neuronal signal?–What is light?–How does light get to the photoreceptors?–What are photoreceptors?–How do photoreceptors transduce light into a neuronal signal?-What is Light?-How does light get to the photoreceptors?XRetinaFoveaHow are images projected onto the retina?a) The orientation is exactly as we see it.b) Left and right are opposite.c) Up and down are opposite.d) Left and right as well as up and down are opposite.Rods ConesOuter Segment StructureDistribution on RetinaSensitivity- What are Photoreceptors?In retinitis pigmentosa, early symptoms include the loss of peripheral vision and night vision. The loss of what type of cells could lead to such symptoms?a) Rodsb) Conesc) Rods and Cones“Dark Current”-How do photoreceptors transduce light into a neuronal signal?Rhodopsin = retinal + opsinPhotopigmentsIn dim light, which type of photoreceptor is more depolarized?a) Rodsb) Conesc) Equally depolarizedSummary•Visible light is a narrow range of electromagnetic radiation that we are able to see•Light travels all the way to the back of our eyes, through several layers of cells on the retina, until it reaches the photopigments in the photoreceptors•There are two types of photoreceptors:–Rods- detect white light, use rhodopsin–Cones- detect color, three varieties of opsins•Photoreceptors are depolarized in the dark because cGMP levels are high, which keeps cGMP-gated Na+ channels open–When light hits, the G-protein transducin is activated, which activates phosphodiesterase, which converts cGMP to GMP, and the cGMP-gated Na+ channels
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