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photochem/electics
vision 1
Question | Answer |
---|---|
what is responsible for conversion of 11-cis retinal to all trans retinal in the visual pigment rhodopsin? | light. as a result: all trans retinal can no longer fit into the binding site on the opsin |
formed in 1 msec as a consequence of opsin undergoing conformational changes in response to light | metarhodopsin II (activated rhodopsin) |
the critical link between the series of photoreceptor reactions and the electrical response is: | metarhodopsin II |
true or false: the all trans retinal is degraded at the end of the light induced chemical reaction | false: it is converted back to the cis retinal form. pigment epithelium is responsible for this. |
the dark current refers to: | a high sodium conductance( there is depolarization in the dark and membrane potential is close to Na+) |
in the rods, if membrane potential is moving closer to K+ equillib potential, the dark current is increased or decreased? | dark current is decreased, meaning the rod receptor is hyperpolarized |
first step of mechanism of Metarhodopsin II: | 1 metarhodopsin activates hundreds of G-proteins called transducin |
second step of mechanism of Metarhodopsin II: | each transducin molecule stimulates a phosphodiesterase molecule |
third step of mechanism of Metarhodopsin II: | each phosphodiesterase molecule hydrolyzes 10^3 cGMP (to GMP). without the cGMP Na+ channels close:dark current is reduced |
what happens to the photoreceptor potential in response to more light? | more hyperpolarization. the response is graded. more light=more hyperpolarized |
when the photoreceptor hyperpolarizes what happens with glutamate(neurotransmitter)? | less glutamate released from photoreceptor |
response of the ganglion cell to excitatory neurotransmitter: | increased action potential activity |