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012 The Absolute and Relative Refractory Periods

Refractory Period? What is that? If you are asking that question, then you want to watch this video.

It explains why you can’t stimulate another action potential at certain times regardless of how strong the stimulus is and why it takes a stronger stimulus to cause another action potential in specific situations.

Check it out, and if you’re left with a question or comment, leave it below.

- Leslie Samuel

Transcript of Today’s Episode

Welcome to another episode of Interactive Biology TV. My name is Leslie Samuel. In this episode, Episode 12, we’re going to be talking about the absolute and relative refractory periods. But before we talk about these refractory periods, let’s look a little bit at voltage-gated sodium channels. Now, we’ve been looking at the action potential, and we’ve said that when a stimulus comes and it makes the membrane potential go above the threshold, we get an action potential. The reason why we get this action potential is because voltage-gated sodium channels open.

Now, voltage-gated sodium channels are very unique, in that they have 3 states that you can find them in. They can either be closed, or they can be open, or they can be inactive. How this works is very simple. They have an activation gate, and they also have an inactivation gate. When the stimulus causes them to open, the activation gate opens, and after 0.5 to 1 millisecond, the inactivation gate automatically closes. What is special about these voltage-gated sodium channels is that once it’s open or inactive, it cannot be re-stimulated to open, because it’s either already opened, or it’s inactivated. With that in mind, let’s go and take a look at what causes the absolute and relative refractory periods.

Here, I am looking at a neuron, and you can see the neuron over here to the right. You know by now the parts of the neuron. Here we have a soma, and then here we have the axon. The main part that we’re going to look at today is what is happening in the axon, like we’ve been looking at in the last few episodes.

If I’m going to look at an action potential and I’m looking at what is happening to the membrane potential, here you can see that we have a stimulus, but it doesn’t cause an impulse. We have another stimulus, but still it does not cause an action potential. But if the stimulus reaches the threshold, we have depolarization. For a review of depolarization, see the episode on depolarization.

What this means is voltage-gated sodium channels (I’m going to write Na+ for sodium ions) open, and sodium rushes into the cell, causing the membrane potential to become more positive. Now, while that is happening, this means that the voltage-gate sodium channels are either open, or they are inactive. So they open first, and after a short period of time, they become inactive. While this is happening, no matter what you do, you cannot cause another action potential, because this one is already on the way, and the voltage-gated sodium channels are either open or inactive. So it does not matter what you do, we will not get another action potential. This is called the absolute refractory period. So we have the ARP, for the absolute refractory period, because the voltage-gated sodium channels are either open or inactive.

As I said in the previous slide, in order for another action potential to happen, those voltage-gated sodium channels need to be reset to close. When we reach the repolarization phase and potassium rushes out, the membrane potential starts going down. As it starts going down, the voltage-gated sodium channels start resetting to their closed state. Once they start resetting to their closed state, you can stimulate it to do another action potential.

However, if there are only a few sodium channels reset, it’s going to take a significantly stronger stimulus to cause the membrane potential to reach the point where we can stimulate the action potential to happen again. I’m going to say that again. When the voltage-gated potassium channels open and potassium ions rush out of the cell, the membrane potential is going to start going down because it’s repolarizing. Once that starts happening, voltage-gated sodium channels start being reset to their closed state. You can stimulate it to have another action potential, but it’s going to take a stronger stimulus since you have fewer channels being reset. That is the relative refractory period (RRP). And that continues, more and more channels are being reset to the closed state, and when they’re all reset to the closed state, that is the end of the relative refractory period.

So you stimulate the axon, you get an action potential, voltage-gated sodium channels are either open or inactive, and you cannot stimulate it again. That is the absolute refractory period. Once they start resetting, you have the relative refractory period, where you can stimulate another action potential, but you will need a stronger stimulus. So that’s the absolute and the relative refractory periods.

I hope it makes sense. That’s all for this video, and I’ll see you in the next one.

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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.

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131 Responses to “012 The Absolute and Relative Refractory Periods”

  1. InteractiveBiology January 10, 2011 at 6:18 am #

    @adeelfromny Glad you find it helpful. Many more coming, so stay tuned :)

  2. InteractiveBiology January 10, 2011 at 1:59 pm #

    @LaSuraya1 Thanks Laura. Glad you like it :D

  3. Akbar M. January 23, 2011 at 12:20 pm #

    Could you please elaborate a bit more on the inactive state of the Na+ channel? How does it differ from the closed state?

    P.S.
    I am a pharmacy student and I think that your videos are great! You explain things so well! Thank you!

    • Leslie January 24, 2011 at 5:31 pm #

      Hi Akbar,

      That’s a great question. I made a video to answer your Question. Here’s the link – http://www.interactive-biology.com/1682/. Hope that helps!

      • Marie St. Louis January 12, 2012 at 12:32 am #

        Could you go more in depth about the inactivation gates more specifically the period of afterhypolarization? During the afterhyperpolarization what’s actually going on?

        • Lrsamuel January 12, 2012 at 7:08 am #

          Hi Marie, unfortunately, I can’t take any special requests anymore due to time limitations. I’m making the videos as I need them for the classes I’m currently teaching.

          All the best!

  4. daniel February 2, 2011 at 7:35 pm #

    how could a cell be modified to increase or decrease the maximal flux of a solute across the plasma membrane by meditated transport mechanism?

    thank you

    • Leslie February 2, 2011 at 7:48 pm #

      Hi Daniel,

      That’s an excellent question. Think about it like this – The factor that regulates the ability of a solute (ions) to cross the membrane would be the presence of those ion-specific channels. It’s kind of like having doors in a building. In order for people to get in, they need to use the door. In order for ions to cross the membrane and get into the house of the cell, it needs to have channels.

      So the question is – If you want to maximize how many people can enter a building, what would you do? Well, you’d probably put more doors. If you want to maximize the flux of a solute across the plasma membrane by mediated transport mechanism, you would want to have more channels available. So, if a cell were to be modified to have more channels, that would increase it’s conductance and allow for a greater flux of the solute.

      Hope that answers your question :)

  5. InteractiveBiology February 14, 2011 at 3:13 pm #

    @katelayt Well, I’m glad I can help. All the best with your class!

  6. InteractiveBiology March 28, 2011 at 1:50 pm #

    @BreatheinStandstill LOL, it’s kinda hard to understand gibberish ;) Glad
    you found value in the videos!

  7. fandanstan July 14, 2011 at 5:46 pm #

    @ediniz101 Basically, a graded potential that causes membrane potential to
    go above threshold initiates an action potential, which causes the ion
    gates to open. The K voltage-gated channels open slower than the Na ones
    do, which is why they open at different times.

  8. Dyan Ybañez July 21, 2011 at 8:54 am #

    thanks a lot… it makes my review so easy to understand… God bless

  9. InteractiveBiology August 20, 2011 at 8:51 pm #

    @warpedoctave Glad to know the videos are helping. Stay tuned for MANY more to come :)

  10. crackowacko87 August 31, 2011 at 9:43 am #

    Hi Leslie, so am I correct to say that the Absolute Refractory period is longer than the Relative Refractory period? Or are they of the same duration? Thanks!

  11. crackowacko87 August 31, 2011 at 9:46 am #

    Hi again Leslie, is it possible you do a lecture video on calcium channels involved in heart contractions? It would really help as I have a thesis to do and I need some tips and assistance in understanding the concepts before I start writing them. Thanks!

  12. InteractiveBiology August 31, 2011 at 11:47 am #

    @crackowacko87 I do have those videos, check out episodes 45 – 47. I deal with those topics there. All the best!

  13. InteractiveBiology August 31, 2011 at 11:50 am #

    @crackowacko87 No, the relative refractory period is longer. It starts at the peak of the action potential and continues until the resting membrane potential is restored. Hope that helps!

  14. sarva khitana Bunbulama September 9, 2011 at 8:08 am #

    Oh I found it. please disregard my request about making a vid about
    refractory period. now I understand, the sodium chanel doesn’t close like
    bang. it closes gradually right? and this causes that the second stimulus
    needs to be stronger than the first one to produce an action potential?!
    thanks for this clip

  15. Djalitana September 9, 2011 at 8:08 am #

    Oh I found it. please disregard my request about making a vid about refractory period. now I understand, the sodium chanel doesn’t close like bang. it closes gradually right? and this causes that the second stimulus needs to be stronger than the first one to produce an action potential?! thanks for this clip

  16. InteractiveBiology September 9, 2011 at 8:14 am #

    @Djalitana No prob. Glad you found it.

  17. InteractiveBiology September 9, 2011 at 8:14 am #

    @Djalitana No prob. Glad you found it.

  18. r3dfreak October 17, 2011 at 1:15 am #

    thanks for the wonderful and clear explanation!

  19. InteractiveBiology October 17, 2011 at 5:52 am #

    @r3dfreak You’re welcome!

  20. InteractiveBiology October 17, 2011 at 5:52 am #

    @r3dfreak You’re welcome!

  21. skinnimelon November 13, 2011 at 2:47 pm #

    thank you!

  22. skinnimelon November 13, 2011 at 2:47 pm #

    thank you!

  23. skinnimelon November 13, 2011 at 2:59 pm #

    The OCR A2 textbook stated that “For a short time after each action potential it is impossible to stimulate the cell membrane to reach another action potential”. Another internet source also said that “Immediately after an action potential, the neurone enters a refractory period”. So does the absolute refractory period occurs before or after an action potential is reached(+40mV)?

  24. skinnimelon November 13, 2011 at 3:13 pm #

    p.s. Is it correct that action potential is not initiated unless the
    potential difference reached +40mV(the peak)?

  25. skinnimelon November 13, 2011 at 3:13 pm #

    p.s. Is it correct that action potential is not initiated unless the potential difference reached +40mV(the peak)?

  26. InteractiveBiology November 14, 2011 at 9:50 am #

    @skinnimelon You’re welcome. Stay tuned for more!

  27. InteractiveBiology November 14, 2011 at 9:54 am #

    Thank you for watching the video. Unfortunately, Leslie is busy at the moment working a lot on improving the site. He is unavailable to answer any more questions. In the meantime, please go to our site directly for more Biology videos. New episodes will be uploaded very soon!

  28. InteractiveBiology November 14, 2011 at 9:54 am #

    @skinnimelon Thank you for watching the video. Unfortunately, Leslie is busy at the moment working a lot on improving the site. He is unavailable to answer any more questions. In the meantime, please go to our site directly for more Biology videos. New episodes will be uploaded very soon!

  29. wackomackopaco November 20, 2011 at 4:21 pm #

    THANK YOU!

  30. wackomackopaco November 20, 2011 at 4:21 pm #

    THANK YOU!

  31. InteractiveBiology November 21, 2011 at 6:27 am #

    You’re welcome! Please stay tuned for more Biology videos! :)

  32. InteractiveBiology November 21, 2011 at 6:27 am #

    @wackomackopaco You’re welcome! Please stay tuned for more Biology videos! :)

  33. NeedsAHardOne November 29, 2011 at 5:35 pm #

    @skinnimelon
    I THINK (if I’m wrong please correct me) an abosolute refractory phase is occurring as long as the Na+ channels are open or inactivated

  34. lindaandjeffsampson November 29, 2011 at 9:53 pm #

    Wow! Great teaching, wish you were my teacher @ school. My teacher goes too fast.

  35. lindaandjeffsampson November 30, 2011 at 2:53 am #

    Wow! Great teaching, wish you were my teacher @ school. My teacher goes too fast.

  36. InteractiveBiology December 1, 2011 at 4:42 am #

    Thank you :) Glad to know you appreciate this. There are more Biology videos in the website that you might want to check out. Stay tuned for more new videos! :)

  37. InteractiveBiology December 1, 2011 at 4:42 am #

    @lindaandjeffsampson Thank you :) Glad to know you appreciate this. There are more Biology videos in the website that you might want to check out. Stay tuned for more new videos! :)

  38. InteractiveBiology December 1, 2011 at 9:42 am #

    Thank you :) Glad to know you appreciate this. There are more Biology videos in the website that you might want to check out. Stay tuned for more new videos! :)

  39. goozbye December 4, 2011 at 6:24 pm #

    You are amazing, thank you so much!!!

  40. InteractiveBiology December 4, 2011 at 9:00 pm #

    You’re very welcome :) Please stay tuned. We have more Biology videos coming to the website soon!

  41. InteractiveBiology December 4, 2011 at 9:00 pm #

    @goozbye You’re very welcome :) Please stay tuned. We have more Biology videos coming to the website soon!

  42. goozbye December 4, 2011 at 11:24 pm #

    You are amazing, thank you so much!!!

  43. InteractiveBiology December 5, 2011 at 2:00 am #

    You’re very welcome :) Please stay tuned. We have more Biology videos coming to the website soon!

  44. thamer7A7 December 7, 2011 at 3:42 pm #

    thank you so much

  45. thamer7A7 December 7, 2011 at 3:42 pm #

    thank you so much

  46. thamer7A7 December 7, 2011 at 8:42 pm #

    thank you so much

  47. InteractiveBiology December 8, 2011 at 3:15 pm #

    You’re welcome! Stay tuned for new Biology videos coming very soon!

  48. InteractiveBiology December 8, 2011 at 3:15 pm #

    @thamer7A7 You’re welcome! Stay tuned for new Biology videos coming very soon!

  49. InteractiveBiology December 8, 2011 at 8:15 pm #

    You’re welcome! Stay tuned for new Biology videos coming very soon!

  50. 2Aboody December 16, 2011 at 12:20 pm #

    thank u for help me to understanding what the different between ARP and RRP

  51. 2Aboody December 16, 2011 at 5:20 pm #

    thank u for help me to understanding what the different between ARP and RRP

  52. UniGirl9008 December 17, 2011 at 9:40 am #

    I have 1 question though, does that mean refractory period = hyperpolarization?

  53. UniGirl9008 December 17, 2011 at 2:40 pm #

    I have 1 question though, does that mean refractory period = hyperpolarization?

  54. InteractiveBiology December 18, 2011 at 5:10 pm #

    @2Aboody Glad we were able to help. Please stay tuned for more Biology learning and fun. We have more Biology videos to be uploaded very soon!

  55. InteractiveBiology December 18, 2011 at 5:10 pm #

    Glad we were able to help. Please stay tuned for more Biology learning and fun. We have more Biology videos to be uploaded very soon!

  56. InteractiveBiology December 18, 2011 at 5:11 pm #

    @UniGirl9008 Unfortunately, Leslie has a lot of things to do at the moment, getting busy with the site, his work, and personal life. He’s not had the time lately to check posts and get back to them. Please do stay tuned though as he’ll be uploading more videos soon that may clarify your question. Thank you!

  57. InteractiveBiology December 18, 2011 at 5:11 pm #

    Unfortunately, Leslie has a lot of things to do at the moment, getting busy with the site, his work, and personal life. He’s not had the time lately to check posts and get back to them. Please do stay tuned though as he’ll be uploading more videos soon that may clarify your question. Thank you!

  58. InteractiveBiology December 18, 2011 at 10:10 pm #

    Glad we were able to help. Please stay tuned for more Biology learning and fun. We have more Biology videos to be uploaded very soon!

  59. InteractiveBiology December 18, 2011 at 10:11 pm #

    Unfortunately, Leslie has a lot of things to do at the moment, getting busy with the site, his work, and personal life. He’s not had the time lately to check posts and get back to them. Please do stay tuned though as he’ll be uploading more videos soon that may clarify your question. Thank you!

  60. LucifersCounterpart January 8, 2012 at 7:17 pm #

    the day just smiled at me :D this is the best channel
    i hav my physiology exam in 2 days n i couldnt understand certain things before finding this channel but as i said grrrrrr8 channel ;D

  61. LucifersCounterpart January 9, 2012 at 12:17 am #

    the day just smiled at me :D this is the best channel
    i hav my physiology exam in 2 days n i couldnt understand certain things before finding this channel but as i said grrrrrr8 channel ;D

  62. yashsaxena1217 January 20, 2012 at 12:32 am #

    @UniGirl9008 Nah, hyperpolarization is a phase not a phase. When the mV drops below -70mV its called hyperploarization, and when it goes back up to -70mV its called polarization. Refractory period is the time it takes for a Na+ channel to open again. This makes sure the action potential moves in one direction.

  63. yashsaxena1217 January 20, 2012 at 12:32 am #

    @UniGirl9008 Nah, hyperpolarization is a phase not a phase. When the mV drops below -70mV its called hyperploarization, and when it goes back up to -70mV its called polarization. Refractory period is the time it takes for a Na+ channel to open again. This makes sure the action potential moves in one direction.

  64. yashsaxena1217 January 20, 2012 at 12:32 am #

    Nah, hyperpolarization is a phase not a phase. When the mV drops below -70mV its called hyperploarization, and when it goes back up to -70mV its called polarization. Refractory period is the time it takes for a Na+ channel to open again. This makes sure the action potential moves in one direction.

  65. yashsaxena1217 January 20, 2012 at 12:32 am #

    Nah, hyperpolarization is a phase not a phase. When the mV drops below -70mV its called hyperploarization, and when it goes back up to -70mV its called polarization. Refractory period is the time it takes for a Na+ channel to open again. This makes sure the action potential moves in one direction.

  66. yashsaxena1217 January 20, 2012 at 5:32 am #

    Nah, hyperpolarization is a phase not a phase. When the mV drops below -70mV its called hyperploarization, and when it goes back up to -70mV its called polarization. Refractory period is the time it takes for a Na+ channel to open again. This makes sure the action potential moves in one direction.

  67. fireandice5969 February 22, 2012 at 9:06 am #

    @UniGirl9008 Refractory period = Repolarization. Hyperpolarization are the K+ ions going further down towards the -90mV range before the pump kicks in to return the Na+ and K+ ions to their resting membrane potential.

  68. fireandice5969 February 22, 2012 at 9:06 am #

    @UniGirl9008 Refractory period = Repolarization. Hyperpolarization are the K+ ions going further down towards the -90mV range before the pump kicks in to return the Na+ and K+ ions to their resting membrane potential.

  69. fireandice5969 February 22, 2012 at 9:06 am #

    Refractory period = Repolarization. Hyperpolarization are the K+ ions going further down towards the -90mV range before the pump kicks in to return the Na+ and K+ ions to their resting membrane potential.

  70. fireandice5969 February 22, 2012 at 2:06 pm #

    Refractory period = Repolarization. Hyperpolarization are the K+ ions going further down towards the -90mV range before the pump kicks in to return the Na+ and K+ ions to their resting membrane potential.

  71. colacasados February 25, 2012 at 4:07 pm #

    Hello, and THANK YOU for your videos!!! They truly simplify information. Would you happen to have videos on ALL of the characteristics of Action Potential (including “nondecremental” & “irreversible”)?

  72. Cola Casados February 25, 2012 at 9:07 pm #

    Hello, and THANK YOU for your videos!!! They truly simplify information. Would you happen to have videos on ALL of the characteristics of Action Potential (including “nondecremental” & “irreversible”)?

  73. Cola Casados February 25, 2012 at 9:07 pm #

    Hello, and THANK YOU for your videos!!! They truly simplify information. Would you happen to have videos on ALL of the characteristics of Action Potential (including “nondecremental” & “irreversible”)?

  74. wahid001 March 1, 2012 at 7:31 pm #

    @InteractiveBiology Or others could contribute to answer some questions while we wait for Leslie.

  75. wahid001 March 1, 2012 at 7:31 pm #

    Or others could contribute to answer some questions while we wait for Leslie.

  76. wahid001 March 1, 2012 at 7:38 pm #

    @UniGirl9008 When voltage-gated Na channels are inactivated, and voltage-gated K channels open. K exits the cell and repolarizes the membrane. At this time, the membrane is in its absolute refractory period.
    When Voltage-gated Na channels change from inactivated to closed. Voltage-gated K channels remain open, causing a hyperpolarization of the membrane. The membrane is now in its relative refractory period.

  77. wahid001 March 1, 2012 at 7:38 pm #

    When voltage-gated Na channels are inactivated, and voltage-gated K channels open. K exits the cell and repolarizes the membrane. At this time, the membrane is in its absolute refractory period.
    When Voltage-gated Na channels change from inactivated to closed. Voltage-gated K channels remain open, causing a hyperpolarization of the membrane. The membrane is now in its relative refractory period.

  78. wahid001 March 2, 2012 at 12:31 am #

    Or others could contribute to answer some questions while we wait for Leslie.

  79. wahid001 March 2, 2012 at 12:38 am #

    When voltage-gated Na channels are inactivated, and voltage-gated K channels open. K exits the cell and repolarizes the membrane. At this time, the membrane is in its absolute refractory period.
    When Voltage-gated Na channels change from inactivated to closed. Voltage-gated K channels remain open, causing a hyperpolarization of the membrane. The membrane is now in its relative refractory period.

  80. alphaWAYNE March 7, 2012 at 9:00 pm #

    Thank you so much for making these videos… You make biology more fun, easy and very understandable… You are a great teacher. A million thank yous.

  81. alphaWAYNE March 8, 2012 at 2:00 am #

    Thank you so much for making these videos… You make biology more fun, easy and very understandable… You are a great teacher. A million thank yous.

  82. ThePhenom94 March 13, 2012 at 9:05 am #

    MAN THANK YOU!
    That was so easy and you explained it better than my teacher!
    ThankYou!

  83. ThePhenom94 March 13, 2012 at 1:05 pm #

    MAN THANK YOU!
    That was so easy and you explained it better than my teacher!
    ThankYou!

  84. landigger March 19, 2012 at 12:22 pm #

    Why Hypocalcemia causes Contraction and Hypercalcemia cause Weakness? hope u can help

  85. landigger March 19, 2012 at 4:22 pm #

    Why Hypocalcemia causes Contraction and Hypercalcemia cause Weakness? hope u can help

  86. Haldouda March 28, 2012 at 2:00 am #

    Does that mean that depolorization= absolute? I mean during depolorization, there is no way to start a new action potential…am i right?

  87. Haldouda March 28, 2012 at 6:00 am #

    Does that mean that depolorization= absolute? I mean during depolorization, there is no way to start a new action potential…am i right?

  88. raxelson1 April 3, 2012 at 7:38 pm #

    Wow thank you so much. That was so easy to understand !!!! Thanks again !

  89. raxelson1 April 3, 2012 at 11:38 pm #

    Wow thank you so much. That was so easy to understand !!!! Thanks again !

  90. kazama246 April 28, 2012 at 3:55 pm #

    you said at repolarization another stimulus must be stronger to trigger an action potential BECAUSE of the fewer sodium channels that were reset…why is that???…anyone help

  91. kazama246 April 28, 2012 at 3:55 pm #

    you said at repolarization another stimulus must be stronger to trigger an action potential BECAUSE of the fewer sodium channels that were reset…why is that???…anyone help

  92. Kim June 1, 2012 at 4:01 am #

    I’m so glad I found out about this wonderful website!!! Thanks so much Leslie, you sure did make biology more fun. You would be an awesome teacher :) thanks so much.

  93. MsMissfay June 1, 2012 at 5:51 pm #

    so helpful thank u :’)

  94. MsMissfay June 1, 2012 at 5:51 pm #

    so helpful thank u :’)

  95. preet July 18, 2012 at 2:19 am #

    wow, your videos are mind blowing.i was sitting in class had no idea what the teacher was talking about.but as soon as i saw a video on you tue about how muscles contarct, everything made so much sense. You really make learning fun, and easy to understand.keep it up.thank you so much for making it available.

  96. eliyunck September 3, 2012 at 1:35 am #

    Given a tracing of membrane potential over time, identify absolute and relative refractory periods?

  97. GeminalAngel September 6, 2012 at 10:45 am #

    I dont think so…
    In refractory period, no stimulus can cause another action potential. till Na gates open up again from their inactivation state. the inactivation gates usualy open up near the RMP after the repolarization has ended. then a strong enough stimulus cna generate another act. potential.
    In hyperpolarization, the membrane is jst depolarized a bit more cuz K channels havent yet closed.
    I maybe wrong :) just sharing wt I know

  98. Daniel Wood September 18, 2012 at 5:32 am #

    I didn’t know the guy from shfifty five knew about action potentials.

  99. Tasha Tolbert November 2, 2012 at 3:32 pm #

    Could you do a video an muscle twitches and excitation-contraction coupling??

  100. lilyctse December 2, 2012 at 5:25 am #

    god bless you !!!

  101. ali aldujaili December 3, 2012 at 9:37 am #

    thanks man

  102. 4thlineforlife January 16, 2013 at 1:45 am #

    guys quick question. after a stimulus when sodium ions rush into the cell and potassium rushes out are these molecules actively transported back to where they were in first place or what?

  103. tandemkrew January 31, 2013 at 10:33 am #

    thanks! This make sense.

  104. JBitzz February 9, 2013 at 2:29 am #

    Hey I heard ur interview on the Smart Passive Income podcast!! Now I’m studying for my neurophysiology midterm and I coincidentally stumbled to your videos haha. Th

  105. NightWanderer01 February 16, 2013 at 7:03 am #

    Yes, Na+/ K+ ATPase restores these ion concentrations back to its resting levels.

  106. NightWanderer01 February 16, 2013 at 7:08 am #

    A refractory period simply refers to the time frame in which the generation of further action potentials may be hindered (RRP) or may not occur at all (ARP). Hyperpolarization, in contrast, describes an event where the cell’s membrane potential drops to levels below its resting potential due to excess K+ leaving the cell. However, it would be correct to say that hyperpolarization could occur during the RELATIVE refractory period (RRP). Hope that helps!

  107. mayank sharma March 7, 2013 at 2:32 am #

    wow… now i got it.. thankyou so much ..

  108. micklo1 March 7, 2013 at 10:50 am #

    Superb! A lesson well learned by this video…. by a great teacher.. I must say. Thanks

  109. baileyp27 March 19, 2013 at 6:37 pm #

    No, the refractory period and the hyperpolarization are separate events that overlap. This graph could use 2 more variables: % of Na channels open; and % of Na channels inactive. You would see that as the AP starts to spike most of the channels go to open, then around the peak most of the channels go to inactive. The relative refractory period actually starts as the voltage is coming back down from the peak as Na channels transition back to closed and ready.

  110. John Guillen March 31, 2013 at 4:11 pm #

    Thank you for your videos. As I read these chapters its kind of hard to understand what’s going on without some kind of picture/video example. But watching your videos and then reading makes more sense.

  111. Kimberly Shell April 9, 2013 at 8:22 pm #

    yes it would be considered a hyperpolarization effect.

  112. Yeeb Xyooj April 29, 2013 at 3:27 pm #

    Thank you for the video. This helps a lot :))

  113. Motahare Vamegh June 7, 2013 at 2:52 pm #

    I totally Understood the concept xD Thank u sooooo muchhhhhhhh :D

  114. 043justdoit June 19, 2013 at 2:40 am #

    yeah using ion transporters(pumps) against concentration gradient

  115. 043justdoit June 19, 2013 at 2:42 am #

    what about M gate and H gate in voltage-gated sodium ion channel?

  116. Diane July 26, 2013 at 7:12 am #

    This is Amazing!

  117. EVI I September 8, 2013 at 6:14 pm #

    Thank you so much! I am taking this in class and you were incredibly helpful!

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  119. KaYuk Yuen September 26, 2013 at 8:12 pm #

    what about supranormal period(SNP)?

  120. suplib October 4, 2013 at 2:30 am #

    The voltage axis shows that the depolarization reaches 40 mV. Isn’t it 30 mV?

  121. Haya Abdulla October 7, 2013 at 3:15 am #

    Very helpful , really appreciate it

  122. Glenda V. October 7, 2013 at 11:48 am #

    Thank YOU, Leslie! God Bless YOU!

  123. mypassioninspiration October 15, 2013 at 11:15 am #

    Thank you, Mr. Samuel!
    You make me confident to get an A for my class! I really appreciate it:]

  124. mypassioninspiration October 15, 2013 at 11:15 am #

    Thank you, Mr. Samuel!
    You make me confident to get an A for my class! I really appreciate it:]

  125. simer sukh October 23, 2013 at 1:29 pm #

    Yes, refractory period means hyperpolarization. Because when repolarization is happening the K+ are leaving through the potassium channels, and they reach their equilibrium of -93mV(below resting state -70mV) which is called hyperpolarization.

  126. Allyson Rodriguez November 3, 2013 at 9:03 am #

    :)

  127. Fazeelat Iftikhar January 26, 2014 at 2:05 am #

    thanks.very helpful