Eye - Pathway of Light vs. Signal Output

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tiredofschool

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I'm getting confused as to the difference between the pathway of light and signal output. I know the signal travels from the retina to the rods/cones --> bipolar cells --> ganglion cells. But the pathway of light is the opposite: ganglion cells --> bipolar cells --> rods/cones.

Or am I just all wrong with this?

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I don't think light goes through the nerves. Light enters the pupil, gets bent and focused through the lens, travels through the vitreous humor and ends up on the retina.

The rods and cones in the retina convert the light signal into a nerve impulse that goes to the brain.

I may have some of the steps confused, or missing. It has been a while since I looked at what the eye does.

hth

dsoz
 
Yeah, I'm on the same page with you but I encountered a question on Berkeley Review's Bio Passage:

Light entering the eye will pass which of these cells first?
A. rod cells
B. cone cells
C. bipolar cells
D. ganglion cells

I could only rule out bipolar cells since those are in between the photoreceptors and ganglion cells. It's difficult to decide between the photoreceptors because I'm assuming light goes through both. But the answer is D - ganglion cells.

Found this too:
eye-diagram.png


Confused...
 
So it looks like the light goes through the ganglion cells, through the bipolar cells, then is DETECTED by the rods and cones. The signal is converted to a nerve impulse that travels through the bipolar cells to the ganglion in cells to the optic tract.
 
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So it looks like the light goes through the ganglion cells, through the bipolar cells, then is DETECTED by the rods and cones. The signal is converted to a nerve impulse that travels through the bipolar cells to the ganglion in cells to the optic tract.

correct, the light needs to pass through all these layers first before reaching the rods/Cones in the innermost part of the retina.
 
I'm getting confused as to the difference between the pathway of light and signal output. I know the signal travels from the retina to the rods/cones --> bipolar cells --> ganglion cells. But the pathway of light is the opposite: ganglion cells --> bipolar cells --> rods/cones.

Or am I just all wrong with this?

You're right. That's because during development, the part of the retina that comes out of the brain actually ends up backing in on itself, and that's why you get a reduction in visual acuity (although we don't notice it) becasue the light then ends up having to travel through layers of neurons (indicated above) before hitting the rod/cone cells (This problem exists in all of Subphylum Craniochordata I believe).

However, the Cephalopods (Eg. Giant squid) have better eyes than us because their retinas don't do the weird reverse thing that ours do in development :eek:

Hope this backstory helps you remember the order of light and signal transmission!
 
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