Action potential questions

[katiesaliba]

1) Could someone please explain the processes of saltatory conduction and local current?
I understand that sodium channels are voltage gated, but I don't understand how the charge travels down the axon of a neuron.

2) How does the refractory period influence the direction in which an impulse will travel?
Action potentials occur during the absolute refractory period, therefore surpassing the threshold. During the relative refractory period, the threshold is dropped too low for a normal stimulus to activate an action potential. Would this affect the direction of an impulse?

3) How is the nervous system able to interpret impulses correctly, considering that action potentials are indistinguishable?
Does the type of neurotransmitter released (inhibitory or excitatory) determine the nature of action potentials?

Thanks 

[slothpomba]

I already answered #1 at great length in your previous thread - Re: Action potential question

At this point its probably a better idea to make "katiesalibas biology thread" and continue to post in there rather than separate threads. Your text under #2 is wrong, action potentials do not occur in the absolute refractory period, that's pretty much its sole characteristic, action potentials cannot be initiated. Revise it.

#3 is probably beyond VCE, where did you get this question?

[katiesaliba]

I already answered #1 at great length in your previous thread - Re: Action potential question

At this point its probably a better idea to make "katiesalibas biology thread" and continue to post in there rather than separate threads. Your text under #2 is wrong, action potentials do not occur in the absolute refractory period, that's pretty much its sole characteristic, action potentials cannot be initiated. Revise it.

#3 is probably beyond VCE, where did you get this question?

Yes, true hahaha
In #2 I meant that the depolarisation and repolarisation stage of the concerned action potential occurs during the refractory period. I know that new ones cannot arise during the period. 

These questions were all from Biozone.

[grannysmith]

Yes, true hahaha
In #2 I meant that the depolarisation and repolarisation stage of the concerned action potential occurs during the refractory period. I know that new ones cannot arise during the period. 

These questions were all from Biozone.

You didn't buy the model answers for Biozone? :p

[katiesaliba]

You didn't buy the model answers for Biozone? :p

Nope, I don't even own the book! haha! some of the worksheets were photocopied for me

[Scooby]

#3 is probably beyond VCE, where did you get this question?

Yeah, again, all of this is really far beyond the course

[thushan]

Nope, I don't even own the book! haha! some of the worksheets were photocopied for me

Biozone is not specified for the VCE course; it is meant to be an 'overall' Biology book for many VCE courses in Australia - don't take its questions as gospel. Follow the study design.

[slothpomba]

Your #1 and #2 questions are actually more related than you might think. In the text under #1, you make reference to the current traveling down the axon. This is actually a crucial idea behind understanding a refractory state or refractoryness. Current can only move down (and not back up) the axon because channels are made refractory. It is key to understand that refractory is a third state for these pumps. You have opened - self explanatory, you have closed and you have refractory. Closed channels can be opened again, its just like locking your door - put the right key in and it'll open again. Refractory channels cannot be opened, this would be like filling your lock full of superglue or cement. It is impossible for them to be opened. They first must pass back into a closed state and then they can be opened again.

Channels that were previously activated become refractory, they are unable to be opened. Current can not "backfire" or travel back up due to this. Ahead of the current are closed channels, yes they are closed but with the right key, they will be opened. For all intents and purposes, the refractory channels before the current are glued shut (for a time, until they become closed).


Here are some more picture i made which may illustrate it further for you. I think the key realisation that needs to be made is that refractory is a third distinct state with special properties, it is different to a closed state.




An AP comes along, closed channels are opened and current starts to move...




Only closed [NOT refractory] channels can be opened. The (closed) channels ahead of the current pulse can be opened, the refractory channels behind it cannot.

[katiesaliba]

Your #1 and #2 questions are actually more related than you might think. In the text under #1, you make reference to the current traveling down the axon. This is actually a crucial idea behind understanding a refractory state or refractoryness. Current can only move down (and not back up) the axon because channels are made refractory. It is key to understand that refractory is a third state for these pumps. You have opened - self explanatory, you have closed and you have refractory. Closed channels can be opened again, its just like locking your door - put the right key in and it'll open again. Refractory channels cannot be opened, this would be like filling your lock full of superglue or cement. It is impossible for them to be opened. They first must pass back into a closed state and then they can be opened again.

Channels that were previously activated become refractory, they are unable to be opened. Current can not "backfire" or travel back up due to this. Ahead of the current are closed channels, yes they are closed but with the right key, they will be opened. For all intents and purposes, the refractory channels before the current are glued shut (for a time, until they become closed).


Here are some more picture i made which may illustrate it further for you. I think the key realisation that needs to be made is that refractory is a third distinct state with special properties, it is different to a closed state.

(Image removed from quote.)


An AP comes along, closed channels are opened and current starts to move...

(Image removed from quote.)


Only closed [NOT refractory] channels can be opened. The (closed) channels ahead of the current pulse can be opened, the refractory channels behind it cannot.

(Image removed from quote.)

Thank you! This is brilliant