TPR free exam question

[chiddler]

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No background information in the passage.

It was noted that when white light was shined into a normal person's eyes, their rod cells hyperpolarized. This is:

a. normal, because rod cells are usually permeable to sodium.
b. normal, because light opens voltage-gated potassium channels in rod cells.
c. abnormal, because rod cells are hyperpolarized at rest.
d. abnormal, because rod cells respond to red light

answer: A.

So I have very little knowledge of how eyes work in terms of action potential stuff. Can I please have an explanation?

 

[bajoneswadup]

No background information in the passage.

It was noted that when white light was shined into a normal person's eyes, their rod cells hyperpolarized. This is:

a. normal, because rod cells are usually permeable to sodium.
b. normal, because light opens voltage-gated potassium channels in rod cells.
c. abnormal, because rod cells are hyperpolarized at rest.
d. abnormal, because rod cells respond to red light

answer: A.

So I have very little knowledge of how eyes work in terms of action potential stuff. Can I please have an explanation?

I'm no pro, but you know your eyes must be permeable to Na+ if they're hyperpolarized (Na/K pump re-establishing resting potential). So C and D are out. And I picked A b/c depolarization is going to happen first, which are Na+ channels (K+ channels are slower to open). I guess the light directly activates Na+ channels. Idk A and B are both tempting

 

[pm1]

No background information in the passage.

It was noted that when white light was shined into a normal person's eyes, their rod cells hyperpolarized. This is:

a. normal, because rod cells are usually permeable to sodium.
b. normal, because light opens voltage-gated potassium channels in rod cells.
c. abnormal, because rod cells are hyperpolarized at rest.
d. abnormal, because rod cells respond to red light

answer: A.

So I have very little knowledge of how eyes work in terms of action potential stuff. Can I please have an explanation?

I don't have my book with me now - ps EK does a good job explaining how eyes work.
If I remember correctly though, eyes work in a funky way. It is kind of the reversal of the normal. When light is not shining through, the neurons are actually hyperpolarized.
From wiki:
"Activation of rods and cones is actually hyperpolarization; when they are not being stimulated, they depolarize and release glutamate continuously."

I can double check and quote from my EK book once I have it with me. Or someone want to add?

 

[pfaction]

No, that's incorrect. In my Glaucoma lecture we learned about the "dark current" and all this fun stuff. The cell is usually depolarized and sending out glutamate which is inhibitory in the eye. (In some places it's excitatory, like interneurons and....****, I forgot my Neuro/Psych course...)

There's phosphodiesterase 5 and transducin that are involved with cGMP. cGMP keeps the Na channel open, when light hits and converts opsin or rhodopsin or whatever (been a year since I took that drugs and disease) transducin and PDE5 are activated, causing cGMP->GMP and the dark current shuts off, so sodium can't enter, hyperpolarization occurs, and glutamate isn't sent to the bipolar cells, which is like saying HEY THERE'S THIS TYPE OF SIGNAL!

 

[chiddler]

Could I have an explanation that would suffice for mcat, please?

I didn't learn about this in my neuro class. Glory of the quarter system. According to my friend i also skipped some very difficult calculus, too 😎

 

[pm1]

Could I have an explanation that would suffice for mcat, please?

I didn't learn about this in my neuro class. Glory of the quarter system. According to my friend i also skipped some very difficult calculus, too 😎

I'm pretty sure that for MCAT purposes we just need to know that the rods and retina are normally depolarized (Na is permeable) but when light goes through it hyperpolarizes.

 

[chiddler]

I'm pretty sure that for MCAT purposes we just need to know that the rods and retina are normally depolarized (Na is permeable) but when light goes through it hyperpolarizes.

great. are you certain? pfaction said it is incorrect. was s/he referring to the first response?

 

[pfaction]

Nah, I was referring to

If I remember correctly though, eyes work in a funky way. It is kind of the reversal of the normal. When light is not shining through, the neurons are actually hyperpolarized.

 

[pm1]

great. are you certain? pfaction said it is incorrect. was s/he referring to the first response?

yes, the first one was wrong sorry. When light goes through they hyper polarize.

 

[MedPR]

Could I have an explanation that would suffice for mcat, please?

I didn't learn about this in my neuro class. Glory of the quarter system. According to my friend i also skipped some very difficult calculus, too 😎

Rods are backwards compared to everything else in terms of depol/hyperpol. Usually when there's some kind of response you think of depolarization (action potential), but rods hyperpolarize in response to light.