Lecture 21

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Cell and Systems Biology
Course Code
Melanie Woodin

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CSB332H1S L21 Apr 02 2012Sensory Systems Responses of Photoreceptors Dark rest inward current into outer segmentdepolarization o Straight line recording in darkLight turns off ongoing inward currentVertebrate photorecs respond w a hyperpolarizationgraded according to intensity of flash R info falls on left side of retinaAnatomical Pathways in the Visual System Optic nerve fibers arise from ganglion cells in retina end in LGNlateral geniculate nucleuspart of thal Visual Pigments LGN axons project to the cerebral cortexConcentrated in membranes of outer segmentsOutput from each retina divides at optic chiasm to supply LGN on eachSensitive molecs sideDense packing in layers traversed by lightR side of each retina projects to R LGN oenhances probability that a photon will be trapped on its oR visual cortex receives info exclusively from L half of way thru outer segment visual field Ex ppl w damaged R cortexblind in left visual field Transduction Darkness Current mostly Na flows into outer segment of both ConvergenceDivergence of Connections rodsconeskeeps segment depolarizedNeurons convergediverge extensively at every stage o V40 mV mo Ex human eye contains 100mil rodscones but only 1mil o Na flows thru stalk NaK pumps reestablish grads ganglion cell axonsLight Closes Na channelsallowing Vm to move towards EK Divergence from V1V
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