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So we’ve gone over Depolarization, Repolarization and Hyperpolarization in some detail. It’s time to do an overall review.
Watch the video above to put everything into perspective and solidify your understanding.
And as usual, you may leave your questions/comments below.
- Leslie Samuel
Transcript of Today’s Episode
Hello and welcome to Interactive Biology TV, where we’re making biology fun! My name is Leslie Samuel. This is Episode 13, where we’re going to be talking about the action potential. I’m basically going to be giving you a review of the concepts that we’ve been talking about up to this point when it comes to the action potential.
Over here, we have our neuron. The part of the neuron that we’re going to be focusing on is the axon, so that’s this region here, starts here and it goes to about there. Now what I’m going to do is I’m going to take a section of the neuron, let’s say I’m going to take this part here and I’m going to draw it down here. So here we have the axon. This is inside the axon, and this is outside the axon.
If you remember from a previous episode, outside the axon, we have a lot of sodium ions. So I’m going to draw sodium ions here, and they are all outside the cell. Now let’s look over here. Here we have a stimulus that’s happening. You can see there’s a first stimulus that does not reach threshold, so nothing happens. Another stimulus comes, it does not reach threshold, so we still do not get an action potential. If we have a stimulus that’s strong enough, and I’m going to draw another stimulus in here. So let’s say we have a stimulus that’s that big. That’s going to reach the threshold and cause an action potential.
When that happens, voltage-gated sodium channels are going to open, and that’s going to cause sodium to rush into the cell. Of course, that’s going to start at the axon hillock. Sodium is going to rush in, making the membrane potential even more positive, causing more channels to open, more sodium to rush in along the axon.
What is that going to do to the membrane potential? You can see right here, this is where we get depolarization. The membrane potential goes up, and it’s trying to reach the Donnan equilibrium for sodium ions. That equilibrium potential is somewhere around 58 millivolts. Sodium is rushing in because of the driving force causing sodium to go in. Sodium wants the membrane potential to go up to its Donnan equilibrium, and that is around 58 millivolts. At this point, voltage-gated potassium channels have enough voltage in order for them to open.
So I’m going to erase all of this now, and we’re going to take at the axon again, I’m going to draw it here in blue. Inside the cell, we have a bunch of potassium ions. Now we have such a positive charge on the inside that potassium ions want to leave, because positive repels positive. When voltage-gated potassium channels open, potassium can now leave the cell. So we have a lot of positive leaving the cell, and what that is going to do is cause repolarization, where the membrane potential is going down. Just like with sodium, potassium wants to reach its equilibrium potential, which is somewhere around -93 millivolts. That is why the membrane potential is going down as it’s leaving, because potassium wants the membrane potential to be at -93 millivolts. That is where it is most comfortable.
Considering that the resting membrane potential is around -70, the membrane potential goes significantly lower than that -70, and this phase we call hyperpolarization. All along this process, we have sodium-potassium pumps that are pumping 3 sodium ions out of the cell, and 2 potassium ions back in. That’s going to cause the membrane potential to eventually reach back to its resting state.
This is the entire action potential, looking at depolarization, repolarization, hyperpolarization, and it getting back to the resting state. I hope that makes sense. If you have any questions, feel free to leave them in the comments below. I’d be happy to answer your question, and even maybe make a video answering your specific question. That’s it for this video, and I’ll see you in the next one.
About The Author Leslie Samuel
Leslie Samuel is the creator of Interactive Biology. He created this site to help Make Biology Fun and has the goal of making this the biggest and best biology resource on the net.
1. February 2012 at 8:04 pm
@InteractiveBiology I LOVED UR VIDEO it was really helpfull with my midterm question 3) Describe how an action potential begins and what happens within the neuron during its transmission. thank you.
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1. February 2012 at 8:04 pm
I LOVED UR VIDEO it was really helpfull with my midterm question 3) Describe how an action potential begins and what happens within the neuron during its transmission. thank you.
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1. February 2012 at 8:04 pm
I LOVED UR VIDEO it was really helpfull with my midterm question 3) Describe how an action potential begins and what happens within the neuron during its transmission. thank you.
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1. February 2012 at 8:04 pm
I LOVED UR VIDEO it was really helpfull with my midterm question 3) Describe how an action potential begins and what happens within the neuron during its transmission. thank you.
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3. February 2012 at 11:06 am
HI Leslie, i dont really get how the sodium-potassium pumping in 3 sodium ions out of the cell, and 2 potassium ions back in that causing the membrane potential back to the resting state…Can you plz explain more about this?
thanks
cheers
o.Jane
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5. February 2012 at 2:43 pm
Thankyou, soo much! i was stuck and after watching your video it all made sense! thanks dude!
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5. February 2012 at 4:58 pm
Thank you so much!!!
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7. February 2012 at 7:05 pm
This was one of the most informative and easy to understand videos I’ve seen on this complex topic. Thank you so much. The combination of your ability to articulate exactly what’s going on inside of a cell during this process and your visual aids was PERFECT! Thank you so much.
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13. February 2012 at 1:58 pm
@InteractiveBiology Great explanation but what I don’t understand is if 2 K+ ions get in the cel and 3 Na+ ions out of the cell, this means that you have a charge of 1 + ( the 1 Na+ ion that goes) that leaves the cell, shouldn’t this mean that there is no hyperpolarization but that the potential even goes lower as a positive charge leaves the cell (netto charge)
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14. February 2012 at 1:25 pm
nice one..thx a lot..
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Leslie Samuel Reply:
February 15th, 2012 at 11:17 am
You’re welcome!
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15. February 2012 at 7:40 pm
thanks for making science fun
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20. February 2012 at 12:31 am
this is a great video
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20. February 2012 at 12:31 am
this is a great video
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20. February 2012 at 10:11 pm
your clips are so helpful, but I have a hard time associating it with the heart. We are currently studying about the action potential of the heart, what happens on the ECG, and how it affects the ions in the heart (Na, K, Ca). Do you have a video that puts it all together. That would save me!!!! Thanks, MJ.
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Leslie Samuel Reply:
February 21st, 2012 at 10:51 pm
Hi MJ, I have multiple videos on the heart. Check out the videos page and look in the section on the Circulatory System. That should help.
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25. February 2012 at 7:09 pm
Is the difference between “membrane potential” & “action potential” the threshold?
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26. February 2012 at 12:21 pm
thanks very helpfull video
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27. February 2012 at 3:24 pm
this guy is super cute and his voice is sexy…this is such an awesome tutorial.
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4. March 2012 at 10:17 am
Thank you very much for explaining Action potentials so well, it really helped me!
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7. March 2012 at 9:13 pm
The best channel so far explaining about biology… and making it more fun! a million thankx to the great teacher Lislie Samuel. Thank you, thank you, thank you.
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9. March 2012 at 7:42 pm
Your seriously making my reading and lectures more understandable wow!
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11. March 2012 at 1:42 pm
Thank you thank you thank you! =) i have an exam tomorrow on this and I was honestly quite confused until I watched your video.
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12. March 2012 at 11:08 am
Brilliant. Thanks for the video.
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14. March 2012 at 7:22 pm
Now this is helpful and so useful. Plus your accent is so nice
Thank you so much!
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18. March 2012 at 5:42 pm
You are seriously an excellent teacher… i understand this completely
Please keep this up and save all the students from terrible teachers. You explain things slowly so it makes sense. Again thanks a lot for this!!
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21. March 2012 at 2:17 am
You are amazing! Thank you!!!!
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21. March 2012 at 2:17 am
You are amazing! Thank you!!!!
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23. March 2012 at 8:06 pm
This has been such a great explanation. I have a test tuesday and this has help me a lot.
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23. March 2012 at 8:06 pm
This has been such a great explanation. I have a test tuesday and this has help me a lot.
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26. March 2012 at 10:17 pm
please help, i have a lab question and im stuck:(
‘With continuous stimulation, how long did the maximal force last ?”thanks
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3. April 2012 at 11:40 am
nice tutorial
i have a question about Na+ – K+ pump, is it still working in state of no action potential? thanks
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3. April 2012 at 3:40 pm
nice tutorial
i have a question about Na+ – K+ pump, is it still working in state of no action potential? thanks
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7. April 2012 at 1:00 am
Thank you for such a nice and informative videos
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7. April 2012 at 11:55 am
man i love you
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8. April 2012 at 12:42 am
I have a couple of questions so it would be great if someone could please help me
At the peak of the action potential, is it the concentration of sodium that causes the repulsion of potassium out of the neuron once the pottasium gated channels open? Are the pottasium ions always in the neuron, or did they enter with the sodium during the action potential?
Also, when the neuron is at rest, what is inside it, which makes it have such a negative resting membrane potential, of about -65mV?
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8. April 2012 at 9:18 am
I am a professor in Psychology and I glean as much as I can from these sources to make my classes that much more interesting. thanks for your vids they’re a real help
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8. April 2012 at 9:18 am
I am a professor in Psychology and I glean as much as I can from these sources to make my classes that much more interesting. thanks for your vids they’re a real help
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15. April 2012 at 12:56 am
WOW! Thank you so much for clarifying the action potential! I was so lost before watching, and now it all makes sense!
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15. April 2012 at 10:18 am
this is fantastic, thank you so much!!! I just couldn’t get my head around it until you started drawing it out on that diagram! thank you thank you thank you!!!
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20. April 2012 at 8:19 pm
Just to clarify.. Potassium channels open at the peak of the action potential and sodium channels open ??
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22. April 2012 at 9:26 pm
OMG THANK U SO MUCH I LOVE UR VIDEOS…after watchin ur video I think am ready for my test..ur wayyyyyy better than my teacher.
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1. May 2012 at 5:48 pm
I’m pretty sure that at the peak sodium channels are closing as the potassium channels are opening to restore the resting membrane potential of -70mV.
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6. May 2012 at 5:03 pm
Why does a hyperpolarization phase generally follow a repolarization phase in a action potential?
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6. May 2012 at 9:36 pm
Nice!!!
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7. May 2012 at 8:17 pm
Thank you!
You made this so clear for me. My book is to confusing.
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7. May 2012 at 8:17 pm
Thank you!
You made this so clear for me. My book is to confusing.
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