Horizontal+Cells+Review

Horizontal+Cells+Review - 1. So let’s start out with just...

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Unformatted text preview: 1. So let’s start out with just stating a fact: there ARE center-on and center-off bipolar cells. The bipolar cells are directly connected only to the CENTER cells, while the surround cells only interact via lateral interactions (horizontal cells). Center-on: -fires MORE (depolarizes) when light is on the middle receptive cells; fires LESS (hyperpolarizes) when light is on the surround -center on uses the sign inverting mGluR6 receptor since light hyperpolarizes (turns off) photoreceptors Center-off: -fires LESS (hyperpolarizes) when light is in the middle receptive cells; fires MORE (depolarizes) when light is in the surround -center-off uses the sign conserving AMPA kainate receptor And remember, for the sake of this topic: hygpolarization = LESS firing/turned off = LESS neurotransmitter release -d__e_polarization = MORE firing/turned on = MORE neurotransmitter release 2. So just to review how horizontal cells work: -in the DARK, photoreceptors DEpolarize (turn on) and release glutamate -horizontal cells release GABA Whenever they receive glutamate from photoreceptors -GABA HYPERpolarizes (turns down) all connected photoreceptors 3. So let’s look at the center-off system first since it’s a bit more straightforward: CENTER-OFF: ALL DARK -center photoreceptor area is initially DEpolarized (turned on) by darkness -ALL cells are depolarized and are releasing glutamate, so all cells trigger horizontal cells to release LOTS of GABA, which HYPERpolarizes (turns down) the center photoreceptors SO: since the photoreceptors are initially DEpolarized and the GABA HYPERpolarizes them, it balances out so that they are neutral or at baseline. 4. CENTER—OFF: CENTER LIT ONLY W4 OW) -center photoreceptor area is HYPERpolarized (turned down) by exposure to light -center photoreceptor area is HYPERpolarized (turned down more) by GABA generated by the darkened surround cells SO: bipolar cell is MOST INACTIVE compared to baseline 5. CENTER-OF F: ALL LIT Q} cm Z W) K (/3474? -center photoreceptor area is HYPERpolarized (turned down) by exposure to light -center photoreceptor area is slightly DEpolarized (turned up) when compared to “center lit” since the light on the surround area has turned off the GABA from the horizontal cells SO: bipolar cell is slightly inactive compared to baseline 6. CENTER-OFF: SURROUND LIT ONLY (/ Z7 * G‘s/W -center photoreceptor area is DEpolarized (turned up) by darkness -center photoreceptor area produces glutamate, which triggers some GABA from the horizontal cell for a slight HYPERpolarization (turns down). SO: bipolar cell is MOST ACTIVE compared to baseline 7. So basically this is what this all looks like relating firing rate to light exposure using a dark-light edge for a center-off: 8. Now, this has all been talking about CENTER-OFF bipolar cells, but the ONLY difference between center-on and center-off is the type of receptors on the bipolar cells. If you use the sign-inverting mGluR6 receptors, then you just reverse everything that was said above. But the important things to take away from all this are: - How center-on and center off bipolar cells are effected by light in different locations 0 ex. light in the center region of a center-on system will create optimal stimulation - That center-on and center-off bipolar cells are only different because of their receptor types — That the effects of the surround cells are created by lateral interactions of horizontal cells 0 glutamate from photoreceptors triggers horizontal cells to release GABA - That this setup increases our sensitivity to edges (light/dark boundaries) ...
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This note was uploaded on 04/14/2010 for the course BIO SCI BIO N110 taught by Professor Leon,chance&parker during the Spring '09 term at UC Irvine.

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Horizontal+Cells+Review - 1. So let’s start out with just...

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