Phototransduciton Cascade Question

[credibleman182]

When Light hits rods, turning it from ON to OFF -> Bipolar cell turns ON -> ganglion cells turns ON..

isn't this the correct one?

but there was a question asking which cells do light entering the eye first, and the answer was Ganglion Cell, not Rod cells ...

can someone explain this to me please? T_T

and also, why would Light hyperpolarize(deactivate) Photoreceptors by turning off Sodium channels? isn't photoreceptors for identifying the colors? shouldn't photoreceptors get activated(depolarized) when light is present?

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[JimKimSlim]

Your understanding is correct, but when light enters the retina, it hits the ganglion cells first, bipolar cells, and then the retinal neurons (cones and rods)! I know it sounds confusing but the photo transduction pathway starts in the back and moves to the front because that’s where the nerves are.

So, when light hits the retina, it flips the structure of the retinal molecule from cis to trans. When retinal is in cis, rod is “ON.” When it comes to physiology, you have to break the generalization that “turning on” is the same as “depolarization”! You need to hyperpolarize some receptors to activate them occasionally!