Get My Best Tips For Passing Biology

Sign up for my newsletter and get my Free Guide!

047 Action Potentials and Contraction in Cardiac Muscle Cells

Leslie explains how action potentials are generated by the cardiac cells of the heart and how the release of calcium can generate heart contraction.

Watch to learn more.

Enjoy!

 

Transcript of Today’s Episode

Hello and welcome to another episode of Interactive-Biology TV where were making Biology fun. My name is Leslie Samuel and in this episode, Episode 47, I’m going to be talking about action potentials and contraction in cardiac muscle cells. So, let’s get right into it.

I’m looking at the heart. We’ve looked at a number of things related to the heart. In the previous episode, we spoke about the SA node, which is what we see here, number one and, we spoke about the AV node, which is this part here, number two, and we spoke about these Purkinje fibers. I’m just going to write PF for now. So, this is the AV node, the SA node and the Purkinje fibers. You can go back to the previous episode to learn more about those, in case you’re not sure what they do; in case you’re not sure how they function.

There are a number of things that I want you to know here. We said that the SA node functions as the pacemaker. There’s an important feature about the heart muscle cells that you need to be aware of. That is the fact that these cells are all electrically connected. So, all of the muscle cells in the ventricle are electrically connected, all of the muscle cells in the atria are also electrically connected.

What that means is that if one of the cells in the ventricle gets stimulated, that signal is going to travel to all of the other cells in the ventricle. Not only that, but, if the SA node starts a signal, that signal is going to spread. This is why we get the heart contracting in response to the signal that’s generated by the SA node. Then, when it reaches the AV node and it spreads via the Purkinje fibers, that signal spreads to all of the muscle cells in the ventricles, causing the ventricles to contract.

There are some other important details that you need to know. When the signal is generated in the SA node and it spreads to the atria, the conduction velocity is one meter per second (1 m/s). So, the signal spreads at a speed of 1 m/s here. At the AV node, it slows down to where it’s somewhere around 0.04m/s. Then, in the Purkinje fibers, it speeds up significantly, and we get a conduction velocity of 5 m/s.

So, what this means is that we have a signal that starts here and spreads throughout the atria relatively quickly at 1 m/s but then, it slows down at the atrioventricular node to 0.04 m/s. So, there’s a delay here, and then, after it passes the atrioventricular node, that signal spreads rapidly to the ventricles. Now, why do we want this? As we mentioned before, the blood first goes to the atria and then, the atria contracts, sending the blood from the atria to the ventricles.

You don’t want the atria and the ventricles contracting at the same time. That would cause problems. You want the ventricles to get filled with the blood from the atria first and then, you want the ventricles to contract sending all that blood to the rest of the body and to the lungs. So, that’s how that works and that is why it’s good that we have this slowing down at the atrioventricular node.

Now that we know that and now that we understand that the muscle cells are all connected electrically, let’s move on and look at what happens inside the muscle cells.

We have a stimulus that comes from the AV node or the SA node and that spreads to the muscle cells. In response to that, what’s going to happen is that the membrane potential of the cardiac muscle cells is all of a sudden going to depolarize very quickly. So, we have that initial depolarization. When the muscle cells depolarize, as with skeletal muscles, we’re going to have calcium being released from the sarcoplasmic reticulum. For a refresher of how that works, you can go back to Episode 42 where I talked about calcium release and how that causes muscle contraction.

Once the calcium is released from the sarcoplasmic reticulum, that’s going to prevent the repolarization that normally happens rather quickly. With a normal neuron, the action potential lasts less than a millisecond. However, in cardiac muscle cells, we have calcium that’s being released that slows down the repolarization process and we get a phase that’s referred to as the ‘plateau.’ The membrane potential does not repolarize as quickly. Then, at a certain point, calcium gets pumped back into the sarcoplasmic reticulum, potassium also leaves as usual, and we get the repolarization of the cardiac muscle cells.

As you can see, the time scale that we have here shows that this action potential can last as much as 300 milliseconds as opposed to the one millisecond or less than one millisecond that we get with a neuron. That’s because of the calcium released. That’s because of this plateau phase.

Let’s see what that does for muscle contraction. Yes, we’re going to have a depolarization but then, we’re going to have the calcium released and that is going to cause the muscle cells to contract just like I showed in Episode 42. Once again, you can always go back at Episode 42 to revisit that concept.

This is what we’re going to do. I’m going to plot the tension in the cardiac muscle cells. So, we’re looking at the cardiac muscle and here, nothing is happening. But, as soon as calcium starts being released, that’s going to cause the muscle cells to contract. This is what’s going to happen. This is the tension and then, once calcium starts being pumped back into the sarcoplasmic reticulum, the muscle cell is going to relax and go back to its resting state.

So, we have the action potential lasting significantly longer than we’ve seen before, because of the calcium that’s released from the sarcoplasmic reticulum and that calcium then causes the muscle cells to contract and we get this tension in the muscle cells.

As the calcium gets pumped back into the sarcoplasmic reticulum and the potassium ions leave, that is going to cause the muscle cells to relax and go back to its original state.

And that’s pretty much it. The action potential causes calcium release. Calcium release causes muscle contraction.

That’s all I’m going to cover in this video. As usual, you can head back to the website at Interactive-Biology.com for more Biology videos and for more resources that we’re adding there on a regular basis. So, stay tuned. This is Leslie Samuel. That’s it for this video and I’ll see you on 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

121 Responses to “047 Action Potentials and Contraction in Cardiac Muscle Cells”

  1. petercourt April 5, 2011 at 8:54 am #

    Thanks for the video! Very helpful. But isn’t the part you’ve labeled Purkenje the left bundle branch of His?

  2. InteractiveBiology April 5, 2011 at 11:31 am #

    @petercourt You are very much welcome.

    You are correct. The bundle of His actually branches off into the Purkinje fibers. Those fibers are the little branches you see. Sorry, my line was a bit off when pointing to the purkinje fibers.

  3. InteractiveBiology April 5, 2011 at 11:31 am #

    You are very much welcome.

    You are correct. The bundle of His actually branches off into the Purkinje fibers. Those fibers are the little branches you see. Sorry, my line was a bit off when pointing to the purkinje fibers.

  4. samia April 8, 2011 at 1:16 pm #

    Hi Lesli, I am really enjoying your videos, that help a lot on my understanding about hear and function. Do you have a page that I can see all the videos related to the cardiovascular system? I really appreciate. keep up…I wish all the teachers could explain in a easy way like you. thanks

    • Leslie April 8, 2011 at 1:27 pm #

      Hi Samia, yes indeed. Just go to the Video Page and you will be able to see all of the videos that are listed. Glad you are finding value in the videos. All the best!

  5. cid6000 April 10, 2011 at 10:34 pm #

    Thank you

  6. InteractiveBiology April 11, 2011 at 11:05 pm #

    @cid6000 You’re very much welcome!

  7. InteractiveBiology April 11, 2011 at 11:05 pm #

    @cid6000 You’re very much welcome!

  8. CecilieWhipps June 11, 2011 at 6:13 am #

    You’re a life saver!

  9. InteractiveBiology June 12, 2011 at 7:47 am #

    @CecilieWhipps We love saving lives. Especially with Biology ;)

  10. InteractiveBiology June 12, 2011 at 7:47 am #

    We love saving lives. Especially with Biology ;)

  11. Corey Sagstuen June 16, 2011 at 4:04 pm #

    Leslie

    That was a great conformation video, I was wondering if you could expand on the depolariaztion a bit and how it directly effects the contraction of the cardiac muscle fibers. In the cardiac muscle fibers in thier resting state they have a similar membrane to teh electrical cells correct??
    With hte release of the Ca ion in hte cells t ocause the depolarisation event to occure and the gap junctions that allow the communication…is it the Ca ion from the electrical cells that crosses thru the gap juntction what sets off the muscle fiber and alters its resting potential..so there si a shift in the Na adn K ions..allowing for the influx of Ca into adn release of Ca from the SR?

    thanks for any help

  12. mrmikeymills September 16, 2011 at 8:32 pm #

    Depolarization lasts less than a ms in skeletal muscle cells? I don’t think so…

    Also, the calcium is not released from the Sarcoplasmic recticulum until voltage gate Ca2+ channels open, allowing EXTRACELLULAR Ca2+ to enter the cell (this is the nature of the plateau), triggering ryanodine receptors to open the gate of the Sarcoplasmic recticulum. Once this happens, then Ca2+ is released from SR, causing calcium spark and triggering the events of the power stroke (muscle contraction).

  13. mrmikeymills September 16, 2011 at 8:32 pm #

    Depolarization lasts less than a ms in skeletal muscle cells? I don’t think so…

    Also, the calcium is not released from the Sarcoplasmic recticulum until voltage gate Ca2+ channels open, allowing EXTRACELLULAR Ca2+ to enter the cell (this is the nature of the plateau), triggering ryanodine receptors to open the gate of the Sarcoplasmic recticulum. Once this happens, then Ca2+ is released from SR, causing calcium spark and triggering the events of the power stroke (muscle contraction).

  14. mrmikeymills September 16, 2011 at 8:32 pm #

    Depolarization lasts less than a ms in skeletal muscle cells? I don’t think
    so… Also, the calcium is not released from the Sarcoplasmic recticulum
    until voltage gate Ca2+ channels open, allowing EXTRACELLULAR Ca2+ to enter
    the cell (this is the nature of the plateau), triggering ryanodine
    receptors to open the gate of the Sarcoplasmic recticulum. Once this
    happens, then Ca2+ is released from SR, causing calcium spark and
    triggering the events of the power stroke (muscle contraction).

  15. yvetreynol September 23, 2011 at 12:35 pm #

    Good job

  16. kerryvp October 28, 2011 at 12:28 pm #

    Are you a Trini??

    Good stuff!

  17. InteractiveBiology October 28, 2011 at 2:00 pm #

    @kerryvp St. Maarten :)

  18. InteractiveBiology October 28, 2011 at 2:00 pm #

    St. Maarten :)

  19. kerryvp October 28, 2011 at 4:28 pm #

    Are you a Trini??

    Good stuff!

  20. InteractiveBiology October 28, 2011 at 6:00 pm #

    St. Maarten :)

  21. lovelylatina207 November 1, 2011 at 11:53 pm #

    Love your intro, Love your voice, you make Biology fun!! :)

  22. lovelylatina207 November 2, 2011 at 3:53 am #

    Love your intro, Love your voice, you make Biology fun!! :)

  23. Anumanu1711 November 15, 2011 at 1:57 pm #

    there is also a phase before Plateau phase, and that is Early Rapid Repolarisation, in which the membrane potential reaches to 0 mv, for opening of L type Can channels, which is necessary for the stimulation of SR Ca channels.

  24. Anumanu1711 November 15, 2011 at 1:57 pm #

    there is also a phase before Plateau phase, and that is Early Rapid Repolarisation, in which the membrane potential reaches to 0 mv, for opening of L type Can channels, which is necessary for the stimulation of SR Ca channels.

  25. Anumanu1711 November 15, 2011 at 6:57 pm #

    there is also a phase before Plateau phase, and that is Early Rapid Repolarisation, in which the membrane potential reaches to 0 mv, for opening of L type Can channels, which is necessary for the stimulation of SR Ca channels.

  26. InteractiveBiology November 16, 2011 at 7:05 am #

    @lovelylatina207 Thank you! Stay tuned for more Biology videos coming very soon!

  27. InteractiveBiology November 16, 2011 at 12:05 pm #

    Thank you! Stay tuned for more Biology videos coming very soon!

  28. jessicg61 November 19, 2011 at 1:29 pm #

    what is the “extra event” that occurs in cardiac muscle?

  29. jessicg61 November 19, 2011 at 6:29 pm #

    what is the “extra event” that occurs in cardiac muscle?

  30. InteractiveBiology November 20, 2011 at 2:17 pm #

    @jessicg61 Hi! Unfortunately, Leslie won’t be able to answer specific questions as he is busy with a lot of work. He will definitely get to more systems in the future. He has many to work on at the moment. So stay tuned for more!

  31. InteractiveBiology November 20, 2011 at 2:17 pm #

    Hi! Unfortunately, Leslie won’t be able to answer specific questions as he is busy with a lot of work. He will definitely get to more systems in the future. He has many to work on at the moment. So stay tuned for more!

  32. InteractiveBiology November 20, 2011 at 7:17 pm #

    Hi! Unfortunately, Leslie won’t be able to answer specific questions as he is busy with a lot of work. He will definitely get to more systems in the future. He has many to work on at the moment. So stay tuned for more!

  33. NeedsAHardOne November 28, 2011 at 9:49 am #

    these viedos are fantastic for review :)

  34. NeedsAHardOne November 28, 2011 at 2:49 pm #

    these viedos are fantastic for review :)

  35. InteractiveBiology November 28, 2011 at 4:12 pm #

    @NeedsAHardOne Thank you! :)

  36. InteractiveBiology November 28, 2011 at 4:12 pm #

    Thank you! :)

  37. InteractiveBiology November 28, 2011 at 9:12 pm #

    Thank you! :)

  38. 19Tranc3r92 December 8, 2011 at 2:02 pm #

    Great video, but a couple errors that bother me.

    - Yes, the Sarcoplasmic Reticulum (SR) does contain Calcium for the troponin re-organization, but the main source of Calcium is not really from the SR, it’s from the (notice too that the SR in Cardiac muscles is a lot less than in skeletal muscles) external environment of the Cardiac muscle.

  39. 19Tranc3r92 December 8, 2011 at 2:02 pm #

    – At the plateu, I think it’s important to mention that the depolarization is maintained b/c of the Calcium coming INTO the cardiac muscle is equal to the Potassium going OUT of the cardiac muscle, not b/c of the Calcium leaving the SR… then there would no change in the voltage.

  40. 19Tranc3r92 December 8, 2011 at 7:02 pm #

    Great video, but a couple errors that bother me.

    - Yes, the Sarcoplasmic Reticulum (SR) does contain Calcium for the troponin re-organization, but the main source of Calcium is not really from the SR, it’s from the (notice too that the SR in Cardiac muscles is a lot less than in skeletal muscles) external environment of the Cardiac muscle.

  41. 19Tranc3r92 December 8, 2011 at 7:02 pm #

    - At the plateu, I think it’s important to mention that the depolarization is maintained b/c of the Calcium coming INTO the cardiac muscle is equal to the Potassium going OUT of the cardiac muscle, not b/c of the Calcium leaving the SR… then there would no change in the voltage.

  42. rounikt December 28, 2011 at 11:43 am #

    @Anumanu1711 ——-absolutely crrct……the early repolarisation phase is missing here……. that produce an inword notch in graph just before onset of plateau …….due toactivation of a trascient outword current carried mainly by k+(efflux of k+)

  43. rounikt December 28, 2011 at 11:43 am #

    @Anumanu1711 ——-absolutely crrct……the early repolarisation phase is missing here……. that produce an inword notch in graph just before onset of plateau …….due toactivation of a trascient outword current carried mainly by k+(efflux of k+)

  44. rounikt December 28, 2011 at 11:43 am #

    ——-absolutely crrct……the early repolarisation phase is missing here……. that produce an inword notch in graph just before onset of plateau …….due toactivation of a trascient outword current carried mainly by k+(efflux of k+)

  45. rounikt December 28, 2011 at 11:43 am #

    ——-absolutely crrct……the early repolarisation phase is missing here……. that produce an inword notch in graph just before onset of plateau …….due toactivation of a trascient outword current carried mainly by k+(efflux of k+)

  46. rounikt December 28, 2011 at 4:43 pm #

    ——-absolutely crrct……the early repolarisation phase is missing here……. that produce an inword notch in graph just before onset of plateau …….due toactivation of a trascient outword current carried mainly by k+(efflux of k+)

  47. walidrahman2 January 3, 2012 at 10:45 pm #

    I was failing one of my biology classes until I found your channel. You are amazing at explaining everything.

  48. walidrahman2 January 4, 2012 at 3:45 am #

    I was failing one of my biology classes until I found your channel. You are amazing at explaining everything.

  49. Nickmysterthe8th January 16, 2012 at 1:40 pm #

    WOW…I Love you. Got a test tomorrow and this was the thing i was struggling with for a while.

  50. Nickmysterthe8th January 16, 2012 at 6:40 pm #

    WOW…I Love you. Got a test tomorrow and this was the thing i was struggling with for a while.

  51. unknownasianchick February 9, 2012 at 2:06 am #

    This saved me hours of reading and stressing over this topic… Very helpful esp. since I have a test tomorrow.

  52. unknownasianchick February 9, 2012 at 7:06 am #

    This saved me hours of reading and stressing over this topic… Very helpful esp. since I have a test tomorrow.

  53. HyperAmygdala February 17, 2012 at 2:54 am #

    It’s 3am,exam at 10:30am. All I can say is Thank You!!!

  54. HyperAmygdala February 17, 2012 at 7:54 am #

    It’s 3am,exam at 10:30am. All I can say is Thank You!!!

  55. wildflower0214 February 29, 2012 at 11:32 pm #

    THANK U, THANK U, THANK U!!! 1 HR AGO I WAS DYING TRYING TO UNDERSTAND THE BOOK!! MY BROTHER SUGGESTED TO COME TO YOUTUBE AND FIND A VIDEO AND NOW I FEEL MUCHHHH BETTER AND CONFIDENT ABOUT MY QUIZ TOMORROW!…

  56. wildflower0214 March 1, 2012 at 4:32 am #

    THANK U, THANK U, THANK U!!! 1 HR AGO I WAS DYING TRYING TO UNDERSTAND THE BOOK!! MY BROTHER SUGGESTED TO COME TO YOUTUBE AND FIND A VIDEO AND NOW I FEEL MUCHHHH BETTER AND CONFIDENT ABOUT MY QUIZ TOMORROW!…

  57. MrGoodClass April 3, 2012 at 1:01 am #

    but what is the purpose of the long refractory period of the action potential? I understand how it works, but why does it need 300 milliseconds as opposed to 1 millisecond in a neuron?

  58. MrGoodClass April 3, 2012 at 5:01 am #

    but what is the purpose of the long refractory period of the action potential? I understand how it works, but why does it need 300 milliseconds as opposed to 1 millisecond in a neuron?

  59. kimmi April 5, 2012 at 5:13 pm #

    hello sir physiology was boring before ..but u made it intrstng lk nythng …..got a tst tmmrw on cardiovascular system …thank u so much fr mkng it simple !!!

  60. qassem93 April 6, 2012 at 7:28 am #

    Very helpful thank you !

  61. qassem93 April 6, 2012 at 7:28 am #

    Very helpful thank you !

  62. qassem93 April 6, 2012 at 11:28 am #

    Very helpful thank you !

  63. Scoffstache April 9, 2012 at 1:16 am #

    gives time for ventricular filling and prevents tetanic contraction

  64. MrGoodClass April 9, 2012 at 4:18 am #

    Thank you :)

  65. MrGoodClass April 9, 2012 at 4:18 am #

    Thank you :)

  66. Scoffstache April 9, 2012 at 5:16 am #

    gives time for ventricular filling and prevents tetanic contraction

  67. MrGoodClass April 9, 2012 at 8:18 am #

    Thank you :)

  68. mirrorreflex April 17, 2012 at 1:56 am #

    Also if the heart did have tetanic contraction it would fatigue, which we do not want as our heart is needed all the time.

  69. mirrorreflex April 17, 2012 at 5:56 am #

    Also if the heart did have tetanic contraction it would fatigue, which we do not want as our heart is needed all the time.

  70. digi aquino April 19, 2012 at 12:33 am #

    love this! helps me prepare for my exam

  71. Claymobileation May 17, 2012 at 12:30 pm #

    I just watched this video to study for a my test today. Thanks.

  72. Claymobileation May 17, 2012 at 12:30 pm #

    I just watched this video to study for a my test today. Thanks.

  73. SuperM3aned May 30, 2012 at 1:46 pm #

    you are my hero doctor <3 .. love u so much

  74. SuperM3aned May 30, 2012 at 1:46 pm #

    you are my hero doctor <3 .. love u so much

  75. SuperM3aned May 30, 2012 at 1:46 pm #

    you are my hero doctor <3 .. love u so much

  76. moogleloveable June 9, 2012 at 6:13 pm #

    love this video series!! great lecturer!!!!

  77. moogleloveable June 9, 2012 at 6:13 pm #

    love this video series!! great lecturer!!!!

  78. sabah1242 June 19, 2012 at 5:36 pm #

    the videos are really good for revision! thankyou!
    can i just ask tho, in smooth/skeletal muscles, calcium is released aswell from the sarcoplasmic reticulum so why doesnt that result in a plateau phase..? is it to do with the timings, because action potentials are time dependent also?

  79. sabah1242 June 19, 2012 at 5:36 pm #

    the videos are really good for revision! thankyou!
    can i just ask tho, in smooth/skeletal muscles, calcium is released aswell from the sarcoplasmic reticulum so why doesnt that result in a plateau phase..? is it to do with the timings, because action potentials are time dependent also?

  80. Priscilla Alameda August 27, 2012 at 3:24 pm #

    Will appreciate it if the Bundle of His was also mentioned…Thanks! =) The videos are REALLY helpful. Good job!

  81. ldyluv6988 September 4, 2012 at 6:23 am #

    THANK YOUU SO MUCH FOR THIS! i UNDERSTAND THIS NOW!!

  82. zahoor ahmad September 30, 2012 at 6:18 am #

    Have you heard about Max Muscle Madness? (check it out on google) It is a quick way to bulk up fast.

  83. Imane smaili October 24, 2012 at 10:53 pm #

    Thank u so much for these videos

  84. packerfan43042 November 1, 2012 at 3:51 pm #

    Very great videos! Greats Appreciated.

  85. youn9024 November 20, 2012 at 10:59 am #

    Bundle of His = AV bundle :)

  86. UtubeDeShayna December 12, 2012 at 11:07 pm #

    You’re videos so unbelievably helpful. Thank you so much for being such a genius but still being able to relay the information!

  87. foxmon1234 December 28, 2012 at 4:24 pm #

    @rpinicy yes. before I started eating right it didn’t matter how much I exercised my abs were still jello. And One of my friend working in fitness field suggested me this 7 secret food items to kill our jelly belly. you can watch out here > bit.ly/Uy4CM8?=qbbcdn

  88. iris prince January 7, 2013 at 8:25 am #

    Great! i hav an exam after tomoroow i needed this thanx

  89. Ayesha Thandeniya January 29, 2013 at 11:02 pm #

    Howdy. I adore the movie. My brother’s entire body grew super quick like he had been injecting steroid drugs. Haha… Turns out the man is not. The guy obtained 32 pounds of lean muscle mass. I’ve constantly struggled to put on muscle mass. He made use of the Muscle Building Bible (google or bing it)

  90. Ayesha Thandeniya January 29, 2013 at 11:05 pm #

    Howdy. I adore the movie. My brother’s entire body grew super quick like he had been injecting steroid drugs. Haha… Turns out the man is not. The guy obtained 32 pounds of lean muscle mass. I’ve constantly struggled to put on muscle mass. He made use of the Muscle Building Bible (google or bing it)

  91. SuperLsteph January 29, 2013 at 11:32 pm #

    Marvelous video. My buddy’s entire body grew very rapidly, as though he was on anabolic steroids. Turns out this guy isn’t. He added 28lbs of lean muscle. I’ve persistently had trouble to build muscle tissue. My friend made use of the Muscle Building Bible (yahoo or google it) I’m about to try it.

  92. Dzamutka Svrsic January 29, 2013 at 11:50 pm #

    Gday. Handy video footage. My buddy’s entire body grew rapidly – like he was injecting anabolic steroids. Found out the man is not. I’ve constantly fought to gain muscle. He tried the Muscle Building Bible (google it)

  93. Alex Rytikoff February 6, 2013 at 3:44 am #

    thank you, that was great demo

  94. walliatbami February 25, 2013 at 6:54 pm #

    Mr. Leslie
    Thank you so much for these fantastic videos :)
    They are great

  95. Jameel Singh March 6, 2013 at 2:32 pm #

    Used this to study for my MCAT. Very good videos. Will be looking for Kidneys next lol

  96. Niyaz Khan March 7, 2013 at 11:44 am #

    Have you tried Max Muscle Method? (Go google it) It is a quick and easy way to get ripped fast.

  97. eslam naser March 9, 2013 at 9:53 am #

    It would be a shame for you not to build muscle when normal people accomplish it so easily using Atomic Max Muscle (check it out on Google).

  98. anas lahrichi March 22, 2013 at 3:55 pm #

    Where is the bundle of his located ? Has it the same role ?

  99. Mobimobipopo April 10, 2013 at 8:04 am #

    Does The action potential includes Depolarisation phase and the plateau?

  100. Justin Forester April 15, 2013 at 7:26 pm #

    Yes. AP ends once it reaches the resting potential again.

  101. محمد العريان May 5, 2013 at 2:54 pm #

    If your desire is to gain some muscle, you may want to Google search for “Oak Muscle Method”. You are bound to end up getting the muscles you want.

  102. provitaminjets June 5, 2013 at 8:52 pm #

    man your freakin amazing man! i’ve been watching your videos and mastering human phys. every time i have an epiphany, and convince myself something is one way, i watch your videos and you clear things up. really appreciate your dedication, live from central canada thank you very much sir.

  103. Nowa Randall Crosby June 18, 2013 at 10:56 pm #

    Thank you!

  104. bruisedvein June 19, 2013 at 6:15 pm #

    this is most excellent <3

  105. RR R. July 2, 2013 at 7:40 am #

    Awesome! Thank you sooo much for these amazing videos. Textbooks make it so difficult to understand but you take very difficult material and concepts and actually manage to make it understandable in less than 10 minutes! God bless you!!!!!!

  106. Cloptonmvb777 July 6, 2013 at 11:44 am #

    Hey YouTubers, have you discovered Morsch Muscle Madness? (just google it) You will find out about the crimes we commit against our bodies. With Morsch Muscle Madness, you will discover how to build muscle quickly.

  107. Cloptonmvb777 July 6, 2013 at 11:44 am #

    Hey YouTubers, have you discovered Morsch Muscle Madness? (just google it) You will find out about the crimes we commit against our bodies. With Morsch Muscle Madness, you will discover how to build muscle quickly.

  108. taigo078 July 9, 2013 at 2:09 pm #

    Great tutororials ! Thank you very much … I just subscribed at your web page for free videos @ interactive-biology

  109. MaryOwens631 July 16, 2013 at 7:39 pm #

    They laughed when I told them I would bulk up with Max Muscle Method, but then I showed them the results. Go and google Max Muscle Method to see their reaction.

  110. DianeHicks349 July 17, 2013 at 11:18 am #

    It would be a shame for you not to get stronger when normal people are able to bulk up so easily using Max Muscle Method (Google it).

  111. vidhya khadka July 19, 2013 at 7:35 am #

    It would be a shame if you did not gain weight and get ripped when average people can so easily with Aston Muscle Ripper (Look it up on google).

  112. Teratoma September 15, 2013 at 9:23 pm #

    You are the man

  113. sendiep September 20, 2013 at 10:54 pm #

    You are the best!!

  114. adam Kemp September 22, 2013 at 1:08 pm #

    Excellent video. A great refresher for me. Thank you!

  115. brumified October 9, 2013 at 9:06 pm #

    @anas lahrichi The bundle of His is a cluster if specialised conduction myocardiocytes, they transmit that electrical energy from the AV node to the Purkenje Fibres; so they function to transmit charge Moreno than concentrate it as in the AV node cardiomyocytes.

  116. brumified October 9, 2013 at 9:07 pm #

    Moreso* Also they extend directly from the AV node

  117. Susan October 24, 2013 at 7:54 pm #

    This was super helpful! Thank you :D

  118. Cile Mile October 26, 2013 at 7:44 pm #

    Yo yo… Excellent clip. My younger brother was once a fat. He remodeled his body from 293lbs of fat to 218 lbs of pure lean muscle. I could not believe it! I just subscribed personally as I’d like to maximize my build. He made use of the Muscle Building Bible (Search on Google)…

  119. imelda flores November 4, 2013 at 4:12 am #

    thank you. these videos are amazing and have been so helpful