lecture_10_19

lecture_10_19 - IX.B.2.b. Lateral inhibition Sign Reversing...

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Sign Reversing IX.B.2.b. Lateral inhibition
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Output of pink rod strongly hyperpolarized weakly depolarized weakly hyperpolarized Light 1 Light 2 from horizontal to TO rod = sign-reversing Light 1 only Light 2 only Light 2 from rod to horizontal is sign-preserving Light 1 Light hyperpolarizes black rod Rod to horizontal sign preserving horizontal cell hyperpolarizes Shine light 2 horizontal to rod sign-reversing rod depolarizes because hyperpolarization reversed = -1 -1 *1) ( *(-1/2) -1 + 1/2 = -1/2 = 1/2 Therefore if light is shone directly on a photoreceptor it will hyperpolarize. However light shone on a photoreceptor will cause depolarization of the neighboring photoreceptor.
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This is partly what causes center surround organization Therefore if light is shone directly on a photoreceptor it will hyperpolarize. However light shone on a photoreceptor will cause depolarization of the neighboring photoreceptor. Therefore from the perspective of one photoreceptor, light shone on you Æ hyperpolarize Light shone surrounding you Æ depolarize IX.B.2.c Center-surround RFs
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Every On bipolar cell receives direct excitatory input from the photoreceptor above it, and lateral inhibition from the photoreceptors (via horizontal cells) all around it. This gives rise to an On-center receptive field, excited by light in the center, and inhibited by light in the surround. This RF structure is then passed on to the ganglion cell Off-center receptive fields are generated in the same way for Off bipolar and ganglion cells. + Example of the formation of a retinal ganglion cell receptive field from the input of 6 photoreceptors (in reality an RGC cell would receive more inputs) Inputs from different Photoreceptors + - - - - - - One on-center RGC cell To create the RF below ‘Inhibitory (-)’ regions are inhibitory because of horizontal cell synapses The center is excitatory Do you think this is coming from the on or off pathway The on pathway and the sign-reversing Rod-bipolar synapse There are also off- center cells
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Rules of center surround RFs (unless you are given other information) 1) Center is stronger than the surround 2) On-center cells are excited when light is turned on in the center 3) On-center cells are inhibited when light is turned off in the center 4) On-center cells are inhibited when light is turned on in the surround 5) On-center cells are excited when light is turned off in the surround
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This note was uploaded on 11/22/2009 for the course NPB 100 taught by Professor Chapman during the Fall '08 term at UC Davis.

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lecture_10_19 - IX.B.2.b. Lateral inhibition Sign Reversing...

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