Action potential direction - Examkrackers

[capostat]

In Examkrackers, it goes on the desribe the propagation of an action potential--the steps involved. And it has a diagram going from left to right, and above it, the corresponding graph of voltage changes.

Then they say that the action potential is travelling from RIGHT to LEFT.

"The protein channels marked 1 are about to receive the action potential while the protein channels marked 5 have already received the action potential. Therefore, the action potential is traveling from right to left along the membrane; the synapse would be to the left of the portion of the membrane shown."

How does this make sense?

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[jaxasp]

im at work so i don't have the book in front of me, but i remember that the diagram was confusing. remember that the voltages will increase to a positive membrane potential during the AP, and reverts to negative during the relative refractory period. So if its travelling from right to left, the membranes on the right side will be in its refractory period, the middle of the diagram will have the membrane at a positive V, and the left of the diagram will still be at (-) V-resting. When I get home I will try to explain the diagram further but i hope that helps

 

[capostat]

im at work so i don't have the book in front of me, but i remember that the diagram was confusing. remember that the voltages will increase to a positive membrane potential during the AP, and reverts to negative during the relative refractory period. So if its travelling from right to left, the membranes on the right side will be in its refractory period, the middle of the diagram will have the membrane at a positive V, and the left of the diagram will still be at (-) V-resting. When I get home I will try to explain the diagram further but i hope that helps

I'm still confused, but I think you've alerted me to a sort of paradox.

If a diagram of a membrane during an AP represents a still picture, then you can say that the right side of the membrane is in its hyperpolarized stage and it is the LEFT side is the side that hasnt had the action potential pass through it yet. This is the only way I can imagine it can traveling R-->L...It doesnt really make sense otherwise. Even if what i said were true, it could only be possible if the left and right in question were extremely separated.

As you know, the way the book drew it--it was as a Left-to-Right process. I still only really understand that if you started depolarizing on the left, then it means you have to go from left to right.

 

[phillips101]

I would say forget about the diagram. Basically, the AP starts at some position on the neuron, usually books say the axon hillock, but it can really be anywhere, travels towards the axon terminal. Whether this is left to right or right to left doesn't matter, the AP always (well, almost always) travel towards the axon terminal. What you said: "he right side of the membrane is in its hyperpolarized stage and it is the LEFT side is the side that hasnt had the action potential pass through it yet" is correct. But an AP doesn't happen instantaneously all throughout the membrane, it does travel, and in some cases, imagine a motor neuron going from your hip to your feet (I'm making this up, but there are neurons that long), the AP has to travel that whole entire distance.
Not sure if that answered your question, but I tried 🙂

 

[capostat]

yeah i get what you're saying...

it's best i just forget the pic...i just got concerned that there was some conceptual info that i was overlooking, and that would naturally turn out to be one of those test questions that catch alot of ppl.

thanks