010 Repolarization: Phase 2 of the Action Potential

010 Repolarization: Phase 2 of the Action Potential

Ok, so by now you should have an understanding of Depolarization: Phase 1 of the Action Potential. If not, then what are you doing here? Don’t watch this video as yet. Check out the previous video first :)

Now your ready to learn about Phase 2, which is Repolarization. If you need a refresher on what an Action potential is, check out the episode entitled What is and Action Potential.

If you have any questions, leave them below. Enjoy!

- Leslie Samuel

Transcript of Today’s Episode

Hello and welcome to Interactive Biology TV. My name is Leslie Samuel. In this episode, we’re going to be talking about repolarization, which is the second phase of the action potential. Now, if you haven’t watched Episode 9 as yet, stop this video right now and go back to Episode 9. Watch that first, and then watch this second, because this is the second phase of the action potential.

Now, in the first phase, we said sodium rushed in, making the membrane potential more positive because the voltage-gated sodium channels open. Now, you’re going to see a little addition to the set-up, the “Action Potential Simulator” that we had, and you’ll see we have these blue marbles. These blue marbles are to represent potassium ions, or K+. These potassium ions also have a positive charge.

Now, we have all of these positive ions inside the cell, and we have so many potassium ions inside the cell that potassium wants to rush out. But once again, normally, potassium ions cannot just rush out. The voltage-gated potassium channels, which you can see here by this yellow divider, need to open first.

So, sodium rushed in, making the membrane potential very positive, relatively speaking. And because the membrane potential is that positive, that’s enough now to open these voltage-gated potassium channels. And what’s going to happen when the voltage-gated potassium channels open? Well, you guessed it. Potassium is going to do what it wants to do: it’s going to rush out. The equilibrium potential for potassium is negative, so it wants the charge across the membrane to be negative. So, by all of these potassium ions leaving, that makes the membrane potential more negative, and that process is called repolarization.

So first we had depolarization, now we have enough charge for the voltage-gated potassium channels to open. Once those open, potassium ions are going to rush out, making the membrane potential more negative. That’s the second phase of the action potential, repolarization.

If you have any questions about that, as usual, leave me a comment. I’ll be happy to answer your question, and maybe even make a video answering your specific question. That’s all for this video, and I’ll see you in the next one.

144 comments
Ema Akw
Ema Akw

I have a question, and by the way your videos are really awesome. My question is: why is it that the more negative a membrane potential gets, the less likely it is for that cell to get depolarised and the more positive a cell gets, the less likely it is to get depolarised. I thought it shud be the reverse. ?.

Jose Martinez
Jose Martinez

Thank you so much, as an IB student this definitely helps with the huge neurobiology chapters!

Georgina Jahnel
Georgina Jahnel

Thank you! You are helping me so much! Without you I wouldn't even understand a thing of biology. Keep on doing these videos! Greetings from Germany:)

safar
safar

potasium also has positve charge why when goes out side the membrane make it negative or repularization?

cagirl085
cagirl085

Does all three phases of action potential involve equilibrium?

Daniel Fowler
Daniel Fowler

I will try to answer your question...Polarization occurs when their is a difference of charges between two regions. In this case positive outside the axon and negative inside the membrane (before depolarization). Therefore, when their are no longer two opposite charges being attracted to each other like when the sodium rushes in the axon, there is no longer opposite charges attracting which is why scientists call this depolarization (because the neuron loses its polarity!). hope this helped!!

lazer1235
lazer1235

you just earnt yourself a subscriber

ching lau
ching lau

Thank you! but I still got a question.. so does it means depolarisation = removing negative charge and repolarisation = removing positive charge?

jhee anthony
jhee anthony

Thank you for the video! Totally appreciate it!

TTerminatorr
TTerminatorr

Great video bioscience is bit easier, and this was a question we needed to answer for class, thank you.

jesse021891
jesse021891

So calcium doesn't play any role in Action Potential's, I thought they did?

Zoonice
Zoonice

i appreciate you video i am nursing school and i was having a hard time with p wave and qrst, your video help me to understand it better

B PHARM
B PHARM

Sir,this is really informative...but why does the leaving of the potassium ions make the inside negatve again rather than making the outside more negative ? I'm having bit of a difficulty in understanding that, could you please explain ?

tsizemore1982
tsizemore1982

Great video. I was confused prior to watching your video. Now I understand. =) Thanks!

jmk8792
jmk8792

This is so helpful - Thanks!

Deborah Pollack
Deborah Pollack

Your videos are amazing!! I love your examples!! You are really helping me out. Thank you!

bryusuf
bryusuf

can you answer my question I need to know the answer to this question please : explain what is happening at the threshold, rising phase, peak, falling phase of the action potential. thank u

InteractiveBiology
InteractiveBiology

Hi, definitely you can use them. Only make sure to link back to the site at Interactive Biology. Good luck and enjoy!!

RaphaelChino
RaphaelChino

hello sir! do you mind if I use your examples for my presentation in class? I'll be sure to credit you for the awesome information :D

edwaak
edwaak

Thank you so much! Im studying anatomy and physiology at university and your videos make it a lot easier to understand! Wish my lecturers explained it like this!

Fiona Umy
Fiona Umy

THis is so helpful sir. Thanx

3393amanda
3393amanda

This was so clear and really helpful, thank you!

felicita843
felicita843

please can u mak a video 4 mechanism of excitation conduction in unmyelinated and unmyelinated fiber

christine
christine

I am confused where calcium comes into the mix of these channel? I am so confused as to why the body needs these channels etc...??

5431marie
5431marie

Ahhh... I've been trying to understand this for weeks... I just couldn't get it, but this helped so much. It's nice to have something explained in a easy to understand way. Haha

allthruu
allthruu

what was very confusing is now not so much...thx greatly!!! I do hope you are teaching Bio somewhere to someone b/c you make this fun!!!

YaelTheFearless
YaelTheFearless

Thank you! You saved my life! You are so clear and amazing!

YaelTheFearless
YaelTheFearless

Thank you! You saved my life! You are so clear and amazing!

BajanGirlBeautiful
BajanGirlBeautiful

wow...thank you! I was having difficulty understanding this but thank you for making it clearer.

BajanGirlBeautiful
BajanGirlBeautiful

wow...thank you! I was having difficulty understanding this but thank you for making it clearer.

BajanGirlBeautiful
BajanGirlBeautiful

wow...thank you! I was having difficulty understanding this but thank you for making it clearer.

tybruce37
tybruce37

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tybruce37
tybruce37

This video is popular on Egypt

InteractiveBiology
InteractiveBiology

@whatzupdud You're welcome. Please stay tuned for more Biology videos, and fun! :)

InteractiveBiology
InteractiveBiology

@whatzupdud You're welcome. Please stay tuned for more Biology videos, and fun! :)