Get My Best Tips For Passing Biology

Sign up for my newsletter and get my Free Guide!

013 A Review of the Action Potential

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.

 

The following two tabs change content below.
Leslie Samuel is the creator of Interactive Biology. His mission is to use this site to Make Biology fun for people all over the world.

Tags: , , , ,


Leave An AWESOME Comment

290 Responses to “013 A Review of the Action Potential”

  1. Mohammed February 12, 2011 at 5:17 pm #

    Thank you so much for the videos sir, they are very helpful .. i have a question if you could answer it please .. after hyperpolarization ( when the na+/k+ pump take 3na+ out and 2K+ in ) are all the na+ now outside the axon ? and all the K+ ions inside the axon ?! or do some Na+ remain in before another action potentail occurs.

    again thank you very much Sir

  2. Shawn February 18, 2011 at 10:40 am #

    I have been trying to find a video about the resting membrane potential. I stumbled onto your videos, and I really like the way you explain things, but I’m not finding a video simply on resting membrane potential. Does such video exist?

  3. BCampbell March 14, 2011 at 2:49 pm #

    You are amazing! Thank you so much for explaining things so clearly and making it fun!

    • Leslie March 14, 2011 at 6:54 pm #

      Thanks a bunch. Glad you are having fun while learning at the same time :)

  4. varsha April 16, 2011 at 9:11 am #

    thank you very much for the wonderful video.i had a doubt in the concept.why is it that the inner part of the membrane is negatively charged while the outer part of the membrane is positively charged when the neuron is in resting potential??

    • Leslie April 16, 2011 at 8:46 pm #

      For a number of reasons:
      1. The Sodium-Potassium pump pumps 3 Sodium ions out and 2 potassium ions in, both of which have a positive charge. Because both are positively charged, more positive is leaving than entering.
      2. There are negatively charged proteins inside the cell.

      Hope that helps Varsha. Take care!

  5. Denise Smith June 1, 2011 at 4:32 am #

    Thank goodness for your videos they have really helped me to study for my exam. Your interactive biology is so much easier to understand than my college classes. Leslie you really do make biology fun. Thankyou so much. you are an inspiration.

    • Lrsamuel June 1, 2011 at 7:05 am #

      I’m glad to know that the videos are helping you so much. Thanks for your comment.

  6. caitlaneag October 19, 2011 at 8:24 pm #

    This was great! Thank you!

  7. InteractiveBiology October 19, 2011 at 9:58 pm #

    @caitlaneag No prob. Al the best!

  8. lllholder October 22, 2011 at 2:59 pm #

    Great video!

  9. drsoha18 October 24, 2011 at 1:23 am #

    thanks
    your explanation is simple
    like

  10. InteractiveBiology October 24, 2011 at 9:07 am #

    @lllholder Thank you!

  11. InteractiveBiology October 24, 2011 at 9:08 am #

    @drsoha18 You are welcome. Glad you are finding value in it.

  12. courtcusimano022 October 24, 2011 at 11:28 pm #

    I do have one question. My notes say that the unstimulated membrane is permeable to potassium but not sodium. Says something about resting permeabilities reflecting the properties of passive leakage channels within the membrane. I was wondering if you could clarify for me?

  13. babysiss3 October 27, 2011 at 2:56 pm #

    Great summation and great enthusiasm!

  14. sathyahema October 28, 2011 at 9:48 pm #

    Hi Leslie,

    My professor talked about Sodium Chemical channels opening during depolarization. When do they come into the picture, before the Sodium Voltage gated channels or after? Thank you so much for these videos, they are so helpful!

  15. dadalacks October 31, 2011 at 8:13 pm #

    good work dude. When I pass my anatomy exam I promise you I’ll donate. Your efforts are really excellent.

  16. ebanupriyah November 5, 2011 at 6:49 am #

    well explained!!thank you..

  17. InteractiveBiology November 7, 2011 at 8:45 am #

    @ebanupriyah Indeed! You might want to check Leslie’s other Biology videos. Like this one, they will make Biology easier for you to understand. Stay tuned for more.

    Have fun!

  18. helenamazzahutt November 11, 2011 at 8:11 pm #

    Thank you, very helpful sir!

  19. InteractiveBiology November 11, 2011 at 9:06 pm #

    @helenamazzahutt Glad you found value in our Biology videos! Please stay tuned for more uploads coming very soon!

  20. Amethystiii November 17, 2011 at 4:19 pm #

    Thank you!!!! I really can thank you enough!! It so clear!! Really thank you !

  21. InteractiveBiology November 17, 2011 at 9:41 pm #

    @Amethystiii Wow! You’re very welcome. Leslie is great at explaining these complicated things making them seem so simpler. You can go to our site for more of these Biology videos. I’m sure you’ll learn a lot more! :)

  22. richardus November 19, 2011 at 6:27 am #

    mmm… ok… there is one thing I do not understand… the stimulus becomes an electric current, right? and that is a group of electrons travelling… so Na/K help the current to keep flowing???

    I do not really understand what the function of Na and K is…

  23. tmcnuz November 19, 2011 at 10:41 am #

    Very Clear and Concise!!
    The only thing I wish you would describe is the absolute and relative refractory periods.

    Thanks!

  24. InteractiveBiology November 20, 2011 at 2:13 pm #

    @tmcnuz Thank You! Leslie has a lot of stuff to do at the moment working on other Biology videos for the website. He’ll get to more topics soon so, please stay tuned!

  25. InteractiveBiology November 20, 2011 at 2:15 pm #

    @richardus Hi! Thank you for watching the video. Unfortunately, Leslie won’t be able to answer specific questions as he is busy at the moment with a lot of work. But, he’ll also be working on additional Biology videos, so please stay tuned for more!

  26. EvelynNLB December 8, 2011 at 5:53 pm #

    wow your amazing.. just saying.. !

  27. InteractiveBiology December 11, 2011 at 12:15 am #

    @EvelynNLB Thank you! Leslie has more Biology videos in the website that you might find useful. Please stay tuned for more!

  28. hawaiianGurl27 December 11, 2011 at 6:55 pm #

    Amazing! Veeeery helpful. You are an awesome teacher. Thanks a lot! :D

  29. InteractiveBiology December 11, 2011 at 7:45 pm #

    @hawaiianGurl27 Thank you and you’re welcome! :) Please stay tuned. We have more Biology videos coming very soon!

  30. mihae December 17, 2011 at 12:07 pm #

    This is probably the most helpful YouTube channel I have found–universities and colleges should model the way that Leslie teaches and incorporate it into their own teaching! amazing!

  31. punkvijay224 December 18, 2011 at 9:54 am #

    I should really say this, you are just too amazing!! I have my exam due coming tuesday, and your help was just at the right time!! THANKS A LOT!!

    Something that I don’t understand is why do college professor don’t find videos like this so they could improve their performance in the class!!

  32. punkvijay224 December 18, 2011 at 9:54 am #

    I should really say this, you are just too amazing!! I have my exam due coming tuesday, and your help was just at the right time!! THANKS A LOT!!

    Something that I don’t understand is why do college professor don’t find videos like this so they could improve their performance in the class!!

  33. InteractiveBiology December 18, 2011 at 5:28 pm #

    @mihae Thank you, thank you so much! Please stay tuned for more!

  34. InteractiveBiology December 18, 2011 at 5:29 pm #

    @punkvijay224 Thank you! We hope you’ll ace your test. Good luck!

  35. vedprakash551992 December 28, 2011 at 2:44 am #

    nice.

  36. Fariba911 December 29, 2011 at 6:46 am #

    thank you for your clearly and useful explanation :)

  37. Fariba911 December 29, 2011 at 6:46 am #

    thank you for your clearly and useful explanation :)

  38. preacherman9 January 2, 2012 at 3:14 pm #

    I have an exam next Monday and I was recommended to do this. Reading this in a text book was blowing my mind and freaking me out. But watching your 6 videos which took 20 mins and i got it. that is a testament to how good you explain this. Thanks a lot buddy. My biopsychology exam does not seem so bad.

  39. srfangl01 January 7, 2012 at 11:22 pm #

    My neuroscience teacher can definitely take a queue from your lecture! geeesh. Makes so much sense now! Clinical pearls!

  40. 28mydecember12 January 15, 2012 at 6:06 am #

    i do have a question..can you explain about voltage gated slow ca+ channel during repolarization happen..is that also known as plateau phase?

  41. InteractiveBiology January 16, 2012 at 5:31 pm #

    @28mydecember12 That’s in Cardiac muscle contraction. Check out my video entitled Action Potentials and Contraction in Cardiac Muscle Cells

  42. 8nochoa January 21, 2012 at 5:08 pm #

    where do the inactivation gates come into play?

  43. majopmful January 28, 2012 at 1:34 pm #

    Its so awesome..thank you so much……be blessed always

  44. gvo369 January 29, 2012 at 9:51 am #

    Thank you so much for your videos they saved my life! You make everything very easy to understand :)

  45. gaara8356 January 30, 2012 at 8:58 am #

    what is the importance of having refractory period,does it relates with the saltatory conduction?

  46. Foinnse February 1, 2012 at 11:22 am #

    @mihae I absolutely agree. Awesome channel. I will be returning again and again and again…..

  47. Foinnse February 1, 2012 at 11:22 am #

    @mihae I absolutely agree. Awesome channel. I will be returning again and again and again…..

  48. Foinnse February 1, 2012 at 11:22 am #

    I absolutely agree. Awesome channel. I will be returning again and again and again…..

  49. Foinnse February 1, 2012 at 11:22 am #

    I absolutely agree. Awesome channel. I will be returning again and again and again…..

  50. brownboys16 February 1, 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.

  51. brownboys16 February 1, 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.

  52. brownboys16 February 1, 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.

  53. brownboys16 February 1, 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.

  54. brownboys16 February 1, 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.

  55. olivia February 3, 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

  56. FuSideways92 February 5, 2012 at 2:43 pm #

    Thankyou, soo much! i was stuck and after watching your video it all made sense! thanks dude!

  57. miniqita February 5, 2012 at 4:58 pm #

    Thank you so much!!!

  58. ske8975 February 7, 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.

  59. michaelyouth February 13, 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)

  60. siewling February 14, 2012 at 1:25 pm #

    nice one..thx a lot..

  61. nubmaster27 February 15, 2012 at 7:40 pm #

    thanks for making science fun

  62. Cicadasmustdie February 20, 2012 at 12:31 am #

    this is a great video

  63. Cicadasmustdie February 20, 2012 at 12:31 am #

    this is a great video

  64. MJ February 20, 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.

    • Leslie Samuel February 21, 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.

  65. colacasados February 25, 2012 at 7:09 pm #

    Is the difference between “membrane potential” & “action potential” the threshold?

  66. wasswa6 February 26, 2012 at 12:21 pm #

    thanks very helpfull video

  67. cherryfilling1997 February 27, 2012 at 3:24 pm #

    this guy is super cute and his voice is sexy…this is such an awesome tutorial.

  68. Dashaxmegan March 4, 2012 at 10:17 am #

    Thank you very much for explaining Action potentials so well, it really helped me!

  69. alphaWAYNE March 7, 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.

  70. escarface March 9, 2012 at 7:42 pm #

    Your seriously making my reading and lectures more understandable wow!

  71. MissyFinny23 March 11, 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.

  72. quegorrea March 12, 2012 at 11:08 am #

    Brilliant. Thanks for the video.

  73. quegorrea March 12, 2012 at 3:08 pm #

    Brilliant. Thanks for the video.

  74. Destroyer629 March 14, 2012 at 7:22 pm #

    Now this is helpful and so useful. Plus your accent is so nice :D

    Thank you so much!

  75. Destroyer629 March 14, 2012 at 11:22 pm #

    Now this is helpful and so useful. Plus your accent is so nice :D

    Thank you so much!

  76. Jessie March 18, 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!!

  77. birukof510 March 21, 2012 at 2:17 am #

    You are amazing! Thank you!!!!

  78. birukof510 March 21, 2012 at 2:17 am #

    You are amazing! Thank you!!!!

  79. birukof510 March 21, 2012 at 6:17 am #

    You are amazing! Thank you!!!!

  80. janjones25 March 23, 2012 at 8:06 pm #

    This has been such a great explanation. I have a test tuesday and this has help me a lot.

  81. janjones25 March 23, 2012 at 8:06 pm #

    This has been such a great explanation. I have a test tuesday and this has help me a lot.

  82. janjones25 March 24, 2012 at 12:06 am #

    This has been such a great explanation. I have a test tuesday and this has help me a lot.

  83. bupbebuon00 March 26, 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

  84. bupbebuon00 March 27, 2012 at 2:17 am #

    please help, i have a lab question and im stuck:(
    ‘With continuous stimulation, how long did the maximal force last ?”thanks

  85. Frea Petra April 3, 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

  86. Anonymous April 3, 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

  87. Frea Petra April 3, 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

  88. MsTayyabakhan April 7, 2012 at 1:00 am #

    Thank you for such a nice and informative videos

  89. MsTayyabakhan April 7, 2012 at 5:00 am #

    Thank you for such a nice and informative videos

  90. drynwhyl23 April 7, 2012 at 11:55 am #

    man i love you

  91. drynwhyl23 April 7, 2012 at 3:55 pm #

    man i love you

  92. atomikjames April 8, 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?

  93. atomikjames April 8, 2012 at 4:42 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?

  94. ThePakman4 April 8, 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

  95. ThePakman4 April 8, 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

  96. ThePakman4 April 8, 2012 at 1:18 pm #

    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

  97. 333teebee April 15, 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!

  98. 333teebee April 15, 2012 at 4:56 am #

    WOW! Thank you so much for clarifying the action potential! I was so lost before watching, and now it all makes sense!

  99. sandyswimsxoxo April 15, 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!!!

  100. sandyswimsxoxo April 15, 2012 at 2:18 pm #

    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!!!

  101. mamary31 April 20, 2012 at 8:19 pm #

    Just to clarify.. Potassium channels open at the peak of the action potential and sodium channels open ??

  102. mamary31 April 21, 2012 at 12:19 am #

    Just to clarify.. Potassium channels open at the peak of the action potential and sodium channels open ??

  103. kajal4eva April 22, 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.

  104. kajal4eva April 23, 2012 at 1:26 am #

    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.

  105. TheLongRain May 1, 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.

  106. TheLongRain May 1, 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.

  107. ausfire000 May 6, 2012 at 5:03 pm #

    Why does a hyperpolarization phase generally follow a repolarization phase in a action potential?

  108. ausfire000 May 6, 2012 at 5:03 pm #

    Why does a hyperpolarization phase generally follow a repolarization phase in a action potential?

  109. rezaeijavan May 6, 2012 at 9:36 pm #

    Nice!!!

  110. rezaeijavan May 6, 2012 at 9:36 pm #

    Nice!!!

  111. Nati1234L May 7, 2012 at 8:17 pm #

    Thank you!
    You made this so clear for me. My book is to confusing.

  112. Nati1234L May 7, 2012 at 8:17 pm #

    Thank you!
    You made this so clear for me. My book is to confusing.

  113. Nati1234L May 7, 2012 at 8:17 pm #

    Thank you!
    You made this so clear for me. My book is to confusing.

  114. otksu June 1, 2012 at 8:55 pm #

    than u ..
    and thanx Fatmah :*

  115. otksu June 1, 2012 at 8:55 pm #

    than u ..
    and thanx Fatmah :*

  116. emikoisabel June 10, 2012 at 5:58 am #

    You are amazing! Here I was crying about being terrified about my upcoming biology exam and I find your glorious videos. Thank you so much!

  117. emikoisabel June 10, 2012 at 5:58 am #

    You are amazing! Here I was crying about being terrified about my upcoming biology exam and I find your glorious videos. Thank you so much!

  118. alexg5ten July 2, 2012 at 6:16 am #

    Still lost as fuck

  119. alexg5ten July 2, 2012 at 6:16 am #

    Still lost as fuck

  120. tingchanghui July 7, 2012 at 8:58 am #

    Hello, I have a question: you mentioned that after hyperpolarisation at -93mV, the resting membrane potential is restored by the Na+/K+ pump, where 3 Na+ is pumped out for every 2K+ pumped into the cell. Wouldn’t the pump cause the membrane potential to be more negative (i.e. lower than -93mV) rather than restore the resting membrane potential (-70mV), since there is a net loss of positive charge? Thank you, you’ve done a great job :)

  121. tingchanghui July 7, 2012 at 8:58 am #

    Hello, I have a question: you mentioned that after hyperpolarisation at -93mV, the resting membrane potential is restored by the Na+/K+ pump, where 3 Na+ is pumped out for every 2K+ pumped into the cell. Wouldn’t the pump cause the membrane potential to be more negative (i.e. lower than -93mV) rather than restore the resting membrane potential (-70mV), since there is a net loss of positive charge? Thank you, you’ve done a great job :)

  122. godCobain July 14, 2012 at 12:01 am #

    your soothing african voice makes learning this easier. not being sarcastic

  123. godCobain July 14, 2012 at 12:01 am #

    your soothing african voice makes learning this easier. not being sarcastic

  124. LittleSister4949 July 16, 2012 at 7:25 pm #

    Awesome! Most helpful.

  125. LittleSister4949 July 16, 2012 at 7:25 pm #

    Awesome! Most helpful.

  126. Intisar July 23, 2012 at 9:28 am #

    very helpfull
    thanks alot

  127. Leimizar August 10, 2012 at 3:36 pm #

    like :) i’m interested in the same thing…

  128. Emeka Diribe September 6, 2012 at 11:45 pm #

    @tingchanhui based on the numbering, the potential seems to be calibrated as V(in) – V(out). This way, as Na+ ions flow into the cell, + V is achieved. As K+ ions flow out, V (out) gets bigger as V(in) gets smaller. So potential becomes more -. Pinch of salt figurative description! Remember that some K+ channels are leaky and the base potential is maintained partially by that leakiness and a balance of electrical and chemical potentials plus the Na+/ K+ pump.

  129. sid123453 September 7, 2012 at 4:23 am #

    sodium potassium pump:-If three Na+ in and 2 K+ out than membrane potential should decrease????

  130. MrBbsingh September 9, 2012 at 9:02 am #

    Hey, great vid. I was wondering whether you could explain the chloride ions and the inhibitory effects that they have on achieving action potential.
    Thanks

  131. MrBbsingh September 9, 2012 at 9:03 am #

    I am under the same impression!

  132. drpink86 September 9, 2012 at 10:17 pm #

    Great Video!!! Thank you!

    Can you explain to me the accommodation phenomenon on action potentials. I read it over and over and don’t seem to get it :-( Thank you!

  133. kavin raj September 11, 2012 at 12:48 am #

    can u say what is firing level???

  134. cynthia jikason September 12, 2012 at 10:09 pm #

    this is wonderful….i hope to see more of ur videos plizzzzzz

  135. churchboy19 September 16, 2012 at 9:37 pm #

    thanks sooo much

  136. SelinaaaBro10 September 23, 2012 at 3:31 pm #

    Thank you, this video is so helpful for my exam tomorrow!

  137. PandTfilms59 September 23, 2012 at 8:25 pm #

    You never mentioned the refractory period…is it the same as the hyperpolarization?

  138. Rainey Shine September 25, 2012 at 4:40 am #

    The best explanation I came across – thank you for sharing -:)

  139. gkunit September 26, 2012 at 9:22 am #

    Thank you!!!!!!!!!!!!!

  140. nantha balan September 26, 2012 at 2:05 pm #

    can u teach about neuromuscular junction

  141. InteractiveBiology September 26, 2012 at 10:37 pm #

    Please check episode 42 AND 41. Those might help. Thanks!

  142. Anakramirez September 27, 2012 at 11:17 pm #

    thanks soo much very helpful

  143. yanting37 September 28, 2012 at 12:58 pm #

    very clear and makes bio concepts easier to understand! thanks a million! really appreciate your efforts!!:)

  144. Naren Selva September 30, 2012 at 2:23 am #

    Hey I studied my book for about 4 hours to understand this. But this video made me understand the whole process within 5 minutes. This is very clear and will help me in my upcoming exam. I really appreciate your efforts.

  145. Solid5Assassin October 5, 2012 at 8:17 pm #

    you are AWESOME !

  146. cristinajose0324 October 6, 2012 at 1:05 am #

    thanks for that video can you please tell me the events leading to the generation of an action potential

  147. MissATete October 6, 2012 at 5:15 am #

    THANK YOU!

  148. purpleyellowelf October 10, 2012 at 3:06 pm #

    I would like to ask, is that after depolarization, an action potential is generated and then follows repolarization? I’m confused when did action potential is generated.

  149. Luke Bockman October 14, 2012 at 1:55 pm #

    The graphs help a ton. Nice video btw

  150. AlMuthanna AlHazmi October 16, 2012 at 12:39 am #

    the action potential happend when Na+ reach the equilibrium potential state ^^
    i think not sure
    & the wholly process is actually called” action potential ”
    chaaaw

  151. Edward Aveiro October 17, 2012 at 4:29 pm #

    as you said how many Na ions and K ions enter the axon per action potential and also you said that 3 Na ions leave the cell and 2 K ions get in… Is that the Neuron your were talking about…..??

  152. TheStarfish13 October 18, 2012 at 4:29 am #

    Great Video :) thank you

  153. Mel Corner October 23, 2012 at 1:17 am #

    Everything makes sense except for the equilibrium potentials..how did you come up with these numbers, 58mV and -93mV..are those estimates? because by looking at the graphs, it seemed as if they should be less..

  154. itzlala711 October 24, 2012 at 11:39 pm #

    Perfect. Thank you!!

  155. Shana Michelle Franklin October 27, 2012 at 8:47 pm #

    thank you..this was helpful. Shana franklin

  156. Anastasiya Baydar October 29, 2012 at 10:23 am #

    u are amazing thank you very much, it really helped :)

  157. ErikaMacDiarmid October 29, 2012 at 3:33 pm #

    Great explanation!

  158. augumentum October 30, 2012 at 8:17 pm #

    I understand the video. What happened to the CA ions. Are CA K and NA actually in elemental forms during Action Potential in efflux and influx ?

  159. jalel amjed October 31, 2012 at 9:24 am #

    It’s cool!!!

  160. naraeoju November 5, 2012 at 2:32 am #

    thank you !!!! I also wanted to ask you about neuromuscular junction ! I’ll check episode 41~2 !!!

  161. sshackelford89 November 6, 2012 at 10:21 pm #

    When the Na+ and K+ ions are going into/leaving cell during depolarization and repolarization, where are they leaving through? Through the leaky ion channels? thanks

  162. martinakanals November 10, 2012 at 10:42 pm #

    good job

  163. queendiamond1969 November 11, 2012 at 12:36 am #

    This video was helpful but 1 thing I didn’t understand is when repolarization was ending and going into what you have labeled on the diagram as a refractory period (below -70mv). I was a little confused because at 4:32 you point to that refractory area and say that it’s hyperpolarization. Are both of these terms synonymous or are there two different functions going on? Thanks.

  164. Jason Friedman November 13, 2012 at 5:49 pm #

    Excellent Video!!! Clear and concise! Thank you

  165. CJNconor November 16, 2012 at 1:52 am #

    Repolarization is the process in which the membrane potential is attempting to go back to being polarized, whereas hyperpolarization is the process in which the inside of the axon becomes even more negative than the resting membrane potential. When this happens (the inside becomes overly negative), it is called the refractory period.

  166. alwaysdhira November 17, 2012 at 9:47 am #

    thank you so much !

  167. Osamtoo November 17, 2012 at 11:04 pm #

    thanks man… keep up

  168. bijay regmi November 18, 2012 at 2:03 pm #

    can you please clearify the hyperpolarisation phase? .. i didnt get it

  169. woohoozzi November 20, 2012 at 5:00 pm #

    Hyperpolarization is just when the membrane voltage falls below the resting potential (that dip labeled refractory period). It is caused by all the K+ (potassium) ions leaving, making the membrane extra-negative until the sodium-potassium pumps can restore the resting potential.

  170. woohoozzi November 20, 2012 at 5:04 pm #

    If you consider the resting potential to be “polarized” then getting more positive is depolarization, returning is repolarization, and going more negative than the membrane voltage at resting potential is hyperpolarization. This coincides with the refractory period because at this point all the sodium is inside the cell and the potassium is outside — so the neuron is not ready to fire another action potential until pumps reinstate the resting potential.

  171. mxg3d November 26, 2012 at 9:53 pm #

    thank you! this was a nice concise review.

  172. Nikki Clark November 27, 2012 at 1:27 pm #

    Thankyou you’ve made this really simple and it’s so much more concise you can’t get lost in all those processes, thank you!!!! Short sharp explanations are better than long winded ones.

  173. YouHearAboutPluto December 4, 2012 at 3:17 am #

    ohh man you are a beast my friend that was right on point everything was explained i understand it now thank you so very much

  174. Vaibhav Kathuria December 9, 2012 at 3:44 pm #

    wonderfully explained!!

  175. Jeremy Toan December 12, 2012 at 5:41 am #

    Great instructional video. Concise and clearly explained! Thanks so much ;D

  176. David Karlsson December 12, 2012 at 11:45 am #

    How is this different from the cardio-action potential? is there a plateu-phase here to?

  177. IknowUThinkImCool December 17, 2012 at 1:48 am #

    No, there isn’t. The plateau phase in the cardio-action potential is caused by the “balancing out” of the efflux of K+ ions with the influx of Ca2+ ions… :D

  178. jcintro4 December 20, 2012 at 3:44 am #

    this is awesome its major help thank you !!!

  179. sunny4lady December 20, 2012 at 5:57 pm #

    Great video, I understood the process but was missing some information that my book didnt explain so thank you – it clarified it!

  180. tonjatonj December 29, 2012 at 3:09 pm #

    thank you!!!!!!!

  181. gracefacex034 December 31, 2012 at 5:09 pm #

    thank you for this, is the resting state the same as the resting potential?

  182. gracefacex034 December 31, 2012 at 5:13 pm #

    also, are those failed initiations EPSPs??

  183. عادل الحميضي January 2, 2013 at 4:36 pm #

    عاشت ايدك

  184. João Luis Carvalho de Souza January 2, 2013 at 9:40 pm #

    Hi, you made some mistakes in your lecture such as 1) Donnan Equilibrium for Na+, 2) K+ leaves the cell cause positive repels positive and 3) the NaKPump causes the membrane voltage go back to the resting potential after hyperpolarization phase.
    And also how do you want to explain action potentials without say what is threshold?

  185. João Luis Carvalho de Souza January 2, 2013 at 9:43 pm #

    Now I can realize how people don’t understand some kind of phenomena like action potential. People are enjoyng this video and saying that “it was wonderfull’ !!!

  186. eniola fujah-sanni January 5, 2013 at 6:29 pm #

    thank you so much I found this very useful ,because am currently doing my A levels in biology and I never realy understood the action potential but now I do . can u please explain the nerve junctions ,thanks and God bless

  187. Tan Run Yu January 8, 2013 at 10:10 am #

    2+ in, 3+ out means that the inside is getting more negative than the outside of the cell. but the graph (hyperpolarization) shows an increase in the voltage potential ?

  188. Tan Run Yu January 8, 2013 at 12:36 pm #

    2+ in, 3+ out means that the inside is getting more negative than the outside of the cell. but the graph (hyperpolarization) shows an increase in the membrane potential ?

  189. DAHRealTrump January 16, 2013 at 6:16 am #

    Thank you!

  190. ig21100 February 10, 2013 at 9:46 pm #

    I love you!

  191. dlaurezo89 February 15, 2013 at 6:21 am #

    thank u so much! :)

  192. Calzonium February 25, 2013 at 1:36 am #

    This was really helpful. Thank you!!

  193. Emily Cashman February 26, 2013 at 2:59 am #

    Very helpful! Thanks!!!

  194. acooper4lyphe February 26, 2013 at 8:27 pm #

    That was very helpful! This is going to help me on my test tomorrow !

  195. swiss emerald February 27, 2013 at 8:23 am #

    thanx alot Sir.

  196. swiss emerald February 27, 2013 at 8:24 am #

    sir what is rapid depolarization?

  197. dvdjshant February 27, 2013 at 1:18 pm #

    Hi Professor,

    Could you illustrate how the action potential moves down along the axon to the axon terminals?

  198. milrinonss February 28, 2013 at 5:22 pm #

    Super video!

  199. sickfitjaw March 14, 2013 at 5:19 pm #

    This was SO helpful! Simple & straight to the point! Thank you!

  200. peggywonghk March 17, 2013 at 1:21 am #

    so why is the membrane potential more positive when three sodium ions are pumped out and two potassium ions are pumped into the cell?? Wouldn’t that be more negative as one positive ions is gone????? i am so confused!

  201. naa akweley March 22, 2013 at 3:56 am #

    thanks. was very clear.

  202. AM loki March 30, 2013 at 8:27 pm #

    wait a minute, if the Na+ voltage-gated channel only open when the stimulus exceeds the threshold, then how inside of the cell became slightly relatively positive BEFORE it reached the threshold?
    I mean, the Na+ ions can still come in to the cell before it reached the threshold? how?

  203. mage nama March 30, 2013 at 11:05 pm #

    Thanks a ton for the upload. Youtube is great for this form of thing.My friend was previously bullied. He said he was intending to get bigger muscles. I laughed… Right up until in just a few weeks he gained 40 pounds of natural muscle mass. He tried the Muscle Building Bible (Google it). He does not get bullied any longer. :-) I actually subscribed the other day. And the mans emails are excellent!

  204. josiejad April 4, 2013 at 9:57 am #

    Thank you so much! My classmates did a presentation in class, and I couldn’t fully grasp it, but this video really helped me to understand it!

  205. Lynn Vu April 10, 2013 at 11:38 am #

    Thanks

  206. xTvxN41Fx April 11, 2013 at 11:51 am #

    I have read that Na/K pumps do to return sodium ions and potasium ions to thier locations and return potential to resting potential after hyperpolarization, now pump give extracelluar fluid positive charges therfore it make intracellular fluid more negative to no end, this menas is resting potential willn’t return, so what happen?! thanks.

  207. SUN NAIR April 12, 2013 at 3:52 pm #

    Thank you so much! You are the only reason why Im not failing anatomy!

  208. murzur2009 April 13, 2013 at 8:14 pm #

    I’m so glad I found you. You are a great teacher!

  209. kadali vamsikrisna April 14, 2013 at 8:53 am #

    fantatic

  210. emma flour April 18, 2013 at 8:37 pm #

    Dieses Video ist langweilig! (aka this video is boring!!!!!!!)

  211. Mead Badir April 23, 2013 at 7:17 am #

    i dont get it,after hyperpo’, you still pump out 3 K+ for 2 Na+ in, meaning you are doing an efflux of cations, which only drives the potential to a more negative voltage….so why does the membrane go back to its resting point?

  212. Lightbluefire April 23, 2013 at 10:37 pm #

    its 3Na for every 2K

  213. Lightbluefire April 23, 2013 at 10:37 pm #

    its 3Na for every 2K

  214. Lightbluefire April 23, 2013 at 10:41 pm #

    the way I understand it, before hyperpolarization, the voltage is – outside of the axon and + inside, and K+ keeps flowing out, but at a point before it reaches equilibirium, the 3 Na+ for every 2 K+ pump kicks in, meaning that there will be more of a negative gradient inside the cell than outside, where more Na+’s are.

  215. Lightbluefire April 23, 2013 at 10:41 pm #

    the way I understand it, before hyperpolarization, the voltage is – outside of the axon and + inside, and K+ keeps flowing out, but at a point before it reaches equilibirium, the 3 Na+ for every 2 K+ pump kicks in, meaning that there will be more of a negative gradient inside the cell than outside, where more Na+’s are.

  216. whatislovej316 April 24, 2013 at 9:16 am #

    What is the difference between an action potential in muscle and skeletal muscle ?

  217. Kristina Kemshead April 25, 2013 at 4:11 pm #

    VERY helpful, thank you so much!!

  218. CabellaBeauty April 26, 2013 at 7:59 pm #

    Amazing!

  219. Aaron Gawronsky April 29, 2013 at 12:47 am #

    You’re the Fxing MAN!!

  220. naitsirhcjmc April 30, 2013 at 7:32 pm #

    Thank You! great for a quick study guide :)

  221. keone sephuthe May 6, 2013 at 9:02 pm #

    that was awesome i have been having some hard time understanding this thanks man

  222. mistywind08 May 11, 2013 at 1:13 pm #

    THANK YOUUU… Very good explanation!

  223. TheMedsick May 17, 2013 at 10:03 am #

    thank u so much…!!!

  224. Sarah Kostanich May 21, 2013 at 4:25 am #

    Thank you so much! you make it easy and clear to understand and actually finding it quite interesting now :)

  225. charles jimingo May 24, 2013 at 8:47 am #

    thanks very much. what a very good teaching

  226. shna1994h June 1, 2013 at 7:35 pm #

    could you tell me please What is the differences between Action potential and Membrane potential ?

  227. jalel amjed June 3, 2013 at 10:46 am #

    Niceeeeee!!

  228. mohkamel June 4, 2013 at 4:23 am #

    thnxx .. i have exam in 30 minute :D

  229. Anosh Kanag June 10, 2013 at 4:09 am #

    needs to be corrected : this is only relevant to the nodes of ranvier between the sections of the neuron circled not the section circled which is myelinated and does not deal with sodium and potassium channels. apart from that this video is very good

  230. Watchutalkingbout Willis June 11, 2013 at 8:22 am #

    i love ur voice

  231. BlueV Jones June 13, 2013 at 1:23 pm #

    I really like these videos but I have a query. From refractory period to resting potential: If the Na+K+ATPase pumps out 3 Na+ ions for every 2 K+ in the neurone, then the inside of the membrane becomes more negative, and does not restore resting potential. Can you clarify this please? ( I thought it was to do with K+ diffusion from the outside to inside that restored the resting potential)

  232. embids June 14, 2013 at 9:04 am #

    Thank you! This video helped me understand Action Potential a lot better.

  233. embids June 14, 2013 at 9:04 am #

    Thank you! This video helped me understand Action Potential a lot better.

  234. ashna wasman June 16, 2013 at 9:17 am #

    Really helpful video .. thanks

  235. deballah1 July 3, 2013 at 1:12 am #

    your work is truly appreciated,thank you

  236. Kalyca Becktel July 7, 2013 at 5:00 pm #

    Thank you!

    How would we label IPSP and EPSP on a graph such as yours.

  237. jerry41799 July 9, 2013 at 1:27 am #

    thank you so much!!!!!! :D

  238. Lara Romero July 16, 2013 at 2:34 am #

    Thank you so much… I was having such a hard time understanding my professors lecture and the textbook. You explained it so well. KUDOS! :-)

  239. hiral san July 30, 2013 at 12:36 am #

    very clear explaination. thnk you very much.

  240. nazrull haziq July 30, 2013 at 9:58 am #

    Thanks ! i never understand Action Potential thing, but now i can really understand it 100 %!

  241. 4kezzah August 3, 2013 at 12:15 pm #

    how does the stimulus cause the membrane potential to become more positive?

  242. 4kezzah August 3, 2013 at 12:48 pm #

    why does the membrane potential not reach the equilibrium potential for Na+

  243. golfam gh August 14, 2013 at 2:22 pm #

    it was great thank you .

  244. devin knight August 14, 2013 at 7:47 pm #

    i finally got it, your the best

  245. MrTinkasaurus August 21, 2013 at 4:01 am #

    Thank you! I did not understand this in class at all today but I totally get it now. You have a really friendly voice, it makes me feel calm haha :)

  246. Laurie Bergman August 29, 2013 at 1:31 am #

    THANK YOU FOR MAKING THESE VIDEOS. YOU HAVE SAVED ME FROM FAILING MY PSYCHOPHARMACOLOGY CLASS! I HAVE NOT BEEN IN COLLEGE FOR OVER 35 YEARS AND I WAS LITERALLY LOST WHEN I HAD TO LEARN ABOUT THE CNS. YOUR PRESENTATIONS WERE SO EASY TO UNDERSTAND. YOU MAKE IT INTERESTING TO LEARN ABOUT A SUBJECT WHICH WAS INITIALLY OVERWHELMING TO ME TO GRASP. I AM NOT A SCIENCE PERSON BUT YOUR STYLE OF INSTRUCTION HAS MADE ME FEEL MORE CONFIDENT THAT I CAN MASTER THE CONCEPTS. THANK YOU AGAIN SO MUCH.

  247. sam aryan August 30, 2013 at 3:04 pm #

    Hi mr.samuel
    these 3 questions have baffled me for a while,
    Q1:when exactly dose the sodium-potassium pump’s job start?
    1 right after the hyperpolarization 2 as soon as the cell reaches the resting state
    if the assumption #2 is correct then in that case the hyperpolarization is sending K+ out while the pump is pumping K+ in?? is’nt it contradictory or maybe the assumption #1 is correct.
    (plese check out my next comment because youtube doesnt let me to post it all in one comment)

  248. sam aryan August 30, 2013 at 3:05 pm #

    please read the comment below first…
    Q2:IS refactory period the same as the activity of sodium-potassium pump? if the assumption 1 is correct then it can not be said that all that part of the graph which is under the line of resting state is all”refractory state”
    Q3:why the Q and S in ORS complex are under hre isoelectric line?and which one causes the U wave, the depolarization of the purkinje fibers or repolarization of them
    I would mean a lot if you take your time answering my question

  249. daras1871 September 4, 2013 at 3:49 am #

    Hello! I have a question:
    Wouldn’t the potassium stop leaving as the cell starts becoming more negative (cell potential becomes lower than resting potential)?

  250. Alex Seb September 10, 2013 at 2:45 pm #

    The answers is yes! As the cell potential reaches -70mV the potassium channels are closing but “slowly” by the time they close cell potential passes past the -70mV. In other words potassium channels have lag time.

  251. XIIXIIXIIXIIX September 14, 2013 at 10:10 am #

    niiiiice

  252. Remi Trashwolf Ødegård September 14, 2013 at 12:33 pm #

    I really appreciate these videos

  253. Tay Cole September 14, 2013 at 2:30 pm #

    This is going to help me out on my next test. Thank you for posting this video!!

  254. Ritusha Kunkolienkar September 22, 2013 at 7:16 am #

    Interactive Biology is just amazing…. Helped me a lot..

  255. KaYuk Yuen September 24, 2013 at 12:34 pm #

    NICE

  256. SuperKaneification September 24, 2013 at 8:36 pm #

    Thanks for taking time out of your day to make this it really helped me out

  257. Gajan Jegatheeswaran September 29, 2013 at 9:13 pm #

    thank you so much!!!!!!! this video helped me so much

  258. DrAbd El-RaHmAn October 6, 2013 at 10:14 pm #

    you great man

  259. Suheirys Contreras October 8, 2013 at 3:54 pm #

    Thank you!! Very clear explanation.

  260. Azii Mee October 8, 2013 at 5:42 pm #

    Thanks a lot.. <3

  261. soko sama October 10, 2013 at 5:58 am #

    AMAZING !!!!

  262. FernandezYoly October 10, 2013 at 1:07 pm #

    Thank you…….Youre the best!

  263. mrgetrealpeople October 11, 2013 at 4:13 pm #

    So is potassium excitatory meaning it would increase resting threshold or is it potassium inhibitory?

  264. Sheyna Hoitsma October 12, 2013 at 9:35 pm #

    Hello, you are wonderful for doing these videos!
    Can you help me understand the second messengers cAMP and camKII in LTP? also if you could break down LTD that would be very lovely!

  265. terri shewczyk October 12, 2013 at 10:16 pm #

    Leslie is a super great teacher!

  266. T Esco October 16, 2013 at 11:49 am #

    Brilliant. Your explanation and method of instruction is in par, thanks!!!!

  267. Germy E October 21, 2013 at 12:07 pm #

    Very precise, informative, and clear video! Thank you sir ^_^

  268. Pierre Marcelin October 27, 2013 at 6:01 am #

    very informative,it is so clear. Now I have a better understanding of the action potential. 1 question I’d like to ask, why you called at one time of your explanation after K+ open during refractory period, hypopolarization?

  269. Shane Cronin October 28, 2013 at 12:33 am #

    How does this “hyperpolarization” period go back to its resting potential? Do Na+ or K+ enter/re-enter the cell or…?

  270. Lizzette Rojas October 29, 2013 at 12:56 am #

    The Na+/K+ pumps will release 3 Na+ ions and bring 2 K+ ions back in (thats only one cycle but it happens a lot). This will eventually make the membrane potential reach its resting state again. Hope that helped.

  271. hasib nafis October 29, 2013 at 5:56 am #

    Hey guys. Fabulous clip. My dad used to be a fat. He changed his body from 284 lbs of pure fat to 211lbs of natural lean muscle. I couldn’t believe it! I just joined myself as I wanna strengthen. He made use of the Muscle Building Bible (Search on Google)…

  272. hasib nafis October 29, 2013 at 5:56 am #

    Hey guys. Fabulous clip. My dad used to be a fat. He changed his body from 284 lbs of pure fat to 211lbs of natural lean muscle. I couldn’t believe it! I just joined myself as I wanna strengthen. He made use of the Muscle Building Bible (Search on Google)…

  273. Alisha Gates November 1, 2013 at 5:33 pm #

    Thank you! Very helpful!

  274. Allyson Rodriguez November 1, 2013 at 8:22 pm #

    Awesome! love this video….

  275. yallaskate November 2, 2013 at 8:46 pm #

    Hsc biology

  276. Clint Lytle November 5, 2013 at 9:18 pm #

    thank you very helpful

  277. Clint Lytle November 5, 2013 at 9:18 pm #

    thank you very helpful

  278. Clint Lytle November 5, 2013 at 9:18 pm #

    thank you very helpful

  279. Hiyam marie November 8, 2013 at 9:40 am #

    THANK YOU SO MUCH !!

  280. Dany Dennaoui November 8, 2013 at 6:26 pm #

    you have a carribean accent .. :P

  281. Eargasm75 November 13, 2013 at 12:17 pm #

    For repolarization, why would potassium leaving the cell make it more
    negative? I thought K was a negative and sodium was positive.

  282. Eargasm75 November 13, 2013 at 12:17 pm #

    For repolarization, why would potassium leaving the cell make it more
    negative? I thought K was a negative and sodium was positive.

  283. Schipper Remco January 9, 2014 at 4:00 am #

    thanks so much. It really really helps me and gives me hope I can really get through this study.

  284. Ahmed Maher Hawila January 11, 2014 at 5:50 pm #

    how can the nerve respond to a stimulus during -ve after potential ..isn’t this response requires soduim influx .. isn’t its conc reversed ..? please, answer my question .. thank you .