anybody left to answer my question?

My eyes are telling me it's time to go to sleep
but I think I still have lots to study-
Is everyone sleeping?
or studying with me??

I was doing the sample midterm and on #3,

I was wondering why it would be rod cells instead of cones when light hits
because I thought cones were the ones more active at day
so it might be more used or suitable for this question..
(is rod used because it's more sesitive to light? or any other reason?)

and the key says "then when the rod cells stops releasing glutamate the bipolar cell will depolarize and release glutamate onto the retinal ganglion cell."
how do we know if it will depolarize?

and it says "If glutamate is excitatory on the retinal ganglion cell..."
isn't glutamate always excitatory?


what's up with all these "IF"s in the solution? ...

"I was wondering why it would be rod cells instead of cones when light hits
because I thought cones were the ones more active at day
so it might be more used or suitable for this question..
(is rod used because it's more sesitive to light? or any other reason?)"

-It can be rods or cones, for the answer they used rods. They are both activated by light, it's just cones are more sensitive to color (certain parts of the spectrum) and rods are more sensitive to detecting light which is useful at night.

and the key says "then when the rod cells stops releasing glutamate the bipolar cell will depolarize and release glutamate onto the retinal ganglion cell."
how do we know if it will depolarize?

-Some bipolar cells depolarize and some bipolar cells hyperpolarize in the presence of glutamate which is always present in the dark. However, when there is light, glutamate is not released and the bipolar cells that do hyperpolarize, depolarize and visa versa.

and it says "If glutamate is excitatory on the retinal ganglion cell..."
isn't glutamate always excitatory?

As you can see in the previous answer, that glutamate causes the opposite to happen.

then the table on p 1024 is misleading. it classifies glutamate as an excitatory neurotransmitter.

Sorry I changed what I said..It causes the opposite to occur

I'm sorry, but I did not understand the glutamate part.

I get that the hyperpolarized bipolarcell wiil be depoarized when it's exposed to light
and will release glutamate onto the ganglion cell.

Can you please explain the next part?

"If glutamate is excitatory on the retinal ganglion cell, then increased release of the glutamate from the bipolar cell will produce action potentials at a higher frequency."


and.. so..
is glutamate excitatory?
or can be either excitatory and inhibitory....
I thought it was only excitatory..

That's a good question, and I'm not sure of the answer and the book does not go into more details. If a question like that appears, I'm sure you're only going to be expected to say that ganglion will synapse with the bipolar cell that depolarize. I didn't know which neurotransmitter was involved between a bipolar and ganglion cell till I saw the answer to the question and it certainly was not in the book. Don't get too hung up on the wording and good luck!

Haha, well i don't know if any of you are still awake, but in response to your post. Glutamate can act as both an inhibitory neurotransmitter and an excitatory neurotransmitter.

The retinal ganglion part: Ok so remember the crayfish stretch receptor? More stretch = more AP. Imagine the increase in stretch as an excitatory signal. So if Glutamate is acting as an excitatory neurotransmitter on the particular retinal ganglion cell then more APs will fire and thus the frequency the brain receives will be greater.

Note: The glutamate molecule itself is not changing. It is the receptor for glutamate that changes. I don't think she wants you to know crazy detail, just understand that if glutamate causes an excitatory response on the retinal ganglion cell then the freq of AP will increase just as in other examples. (Crayfish stretch)

Hope this helps =)

-Charlie