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045 The Pacemaker Potential of the SA Node and the AV Node

In this episode, Leslie talks about how a pacemaker potential can cause a heart to beat automatically. Details about how it is generated is discussed in this video. Just how does this happen, our heart beating again and again?

Watch to learn more. Have fun and enjoy!

Transcript of Today’s Episode

Hello and welcome to another episode of Interactive-Biology TV where we’re making Biology fun. My name is Leslie Samuel and in this episode, Episode 45, I’m going to be talking about the pacemaker potential of the S.A. node and the A.V. node. We’re basically going to look at how this results in the heart beating automatically. So, let’s get right into it.

Let’s first talk about the S.A. node. The S.A. node stands for the sinoatrial node and you can see it in this figure over here, it is number one. That’s this cluster of cells. It is basically a specialized group of cardiac muscle cells that don’t contract which is kind of strange. They’re muscle cells and they don’t actually contract.

But, what’s special about these cells is that they are adapted to automatically generate impulses. So, it can automatically cause signals that can spread throughout the heart, causing the heart to beat. The S.A. node functions as the pacemaker of the heart. Yes, we have the A.V. node and some other stuff that we are going to talk about but, these generates signals faster than any of the others so, it sets the pace for the heartbeat.

As you can see, it is located in the right atrium. So, now let’s talk about the A.V. node.

The A.V. node is number two. So, it’s this cluster of cells here and it stands for the atrioventricular node. It is similar in function to the S.A. node in that it automatically generates impulses and it is located between the atria and the ventricles hence the name, atrioventricular node. Let’s go back to the S.A. node and see how this results in the pacemaker potential.

Before we look at that, I just want to point out that we have, in addition to the S.A. node and the A.V. node, we have some fibers that extend from the A.V. node and spread throughout the ventricle and those fibers are called Purkinje fibers. These are also very important in that they spread that signal throughout the rest of the ventricle. Let’s talk about the S.A node.

We said that that functions as a pacemaker. So, we are going to look at the pacemaker cells that we have in the S.A. node. What is special about these cells is that normally, there’s a significantly higher conductance for sodium than there is for potassium. Now, if you go back to Episode 006, I talk about Donnan equilibrium and driving force and I show how there’s normally a driving force for sodium to rush into the cell. I also show that potassium wants to leave the cell.

Because the cell is much more permeable to sodium, we’re going to have a situation where there’s much more sodium coming in than potassium leaving. Because we have more positives going in than leaving, what we’re going to get is a pacemaker potential where the cell normally depolarizes. Then, when it reaches the threshold, something interesting happens. Yes, we have the sodium rushing in and some potassium leaving but, now that we’ve reached the threshold, voltage-gated calcium channels open and calcium is going to rush into the cell.

So, we’re going to get this rapid depolarization. In other words, we’re going to get an action potential. At the peak, we’re going to get a different situation where, yes, we have sodium coming in and potassium leaving but, voltage-gated potassium channels are going to open so that the conductance for potassium increases significantly and potassium is going to rush out of the cell repolarizing the membrane.

At that point, we still have the sodium that’s coming in and the voltage-gated potassium channels close so, we have the initial situation where sodium is rushing into the cell, causing this depolarization then, the same thing happens. It reaches the threshold, voltage-gated calcium channels open depolarizing the cell membrane once again, causing that impulse. Voltage-gated potassium channels open causing potassium to rush out of the cell again.

This process continues over and over and over. What ends up happening is we have this automatic signal that’s generated constantly resulting in the contraction of the heart. This causes the heart to beat. It’s really that straightforward but, the main idea is that the cells in the S.A. node have a significantly higher conductance for sodium so it continuously depolarizes causing that impulse that causes the heart to beat.

That’s really all I want to talk about in this video. As usual, you can visit the website at Interactive-Biology.com for more Biology videos and other resources to help make Biology fun.

This is Leslie Samuel. That’s it for this video and I’ll see you on 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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Leave An AWESOME Comment

169 Responses to “045 The Pacemaker Potential of the SA Node and the AV Node”

  1. oya April 28, 2011 at 10:43 am #

    in Vanders Human physiology,it is written that Calcium channel open only briefly and it is an important depolarizing boost to pacemaker potential.
    nice video!(thumbs up)

    • Lrsamuel April 28, 2011 at 10:46 am #

      That’s correct. When the pacemaker potential reaches threshold, the Calcium channels open briefly causing the depolarization. That’s what is illustrated in the video. Glad you like it.

      All the best!

      Leslie

  2. vivienne May 16, 2011 at 10:45 am #

    thanks, you are superb in explaining all that :)

  3. kenzie0201 August 12, 2011 at 4:02 am #

    @Azamspazam91 I almost can’t bare it! :D

  4. InteractiveBiology August 19, 2011 at 9:29 am #

    @tiarafazlin17 I LOVE saving lives with Biology :D – Stay tuned for MANY more, and make sure to share the site with EVERYONE you know who might benefit ;)

  5. madej1858 October 5, 2011 at 10:43 pm #

    i got 87.5 on my first lecture exam , i used your information and i guess it works out really well…. you don’t need be a rocket scientist to understand this.:)

  6. InteractiveBiology October 6, 2011 at 10:05 am #

    @madej1858 WOOHOOOOO, Congrats on your success. Nope, rocket scientist is unnecessary :)

  7. Elnora4ka October 8, 2011 at 11:43 pm #

    That is so helpful! now I finally understood how that system works! Thank
    you!!:)

  8. Elnora4ka October 8, 2011 at 11:43 pm #

    That is so helpful! now I finally understood how that system works! Thank you!!:)

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

    @Elnora4ka You are very much welcome. Glad it helped :)

  10. ruddergrl1 October 9, 2011 at 9:04 pm #

    Do you have any videos that are more specific with the mentioning of funny
    channels/T-type channels/L-type channels and when those, specifically, come
    into the picture, etc?

  11. ruddergrl1 October 9, 2011 at 9:04 pm #

    Do you have any videos that are more specific with the mentioning of funny channels/T-type channels/L-type channels and when those, specifically, come into the picture, etc?

  12. InteractiveBiology October 10, 2011 at 5:40 am #

    @ruddergrl1 I do not. All the best!

  13. zamirahbasher October 14, 2011 at 7:42 pm #

    when the level of potassium is high the heart will start beating irregularly , or leads to Cardioplegia,, why is this so,, what is the mechanism that cause the heart to be in this condition

  14. zamirahbasher October 14, 2011 at 7:42 pm #

    when the level of potassium is high the heart will start beating irregularly , or leads to Cardioplegia,, why is this so,, what is the mechanism that cause the heart to be in this condition

  15. HoneiiDiiva October 15, 2011 at 5:10 pm #

    I have a lab exam soon and this helps me.

  16. HoneiiDiiva October 15, 2011 at 5:10 pm #

    @madej1858 wow that’s a great grade, congrats!

  17. InteractiveBiology October 15, 2011 at 8:35 pm #

    @zamirahbasher All questions are answered in the Interactive Biology community forums from now on. Go to the website in the description and then visit the community. This is to make it as efficient as possible as we have multiple people over there to help answer questions.

    All the best

  18. InteractiveBiology October 15, 2011 at 8:36 pm #

    @HoneiiDiiva Glad to hear. All the best on your exam. Let me know how it
    went!

  19. InteractiveBiology October 15, 2011 at 8:36 pm #

    @HoneiiDiiva Glad to hear. All the best on your exam. Let me know how it went!

  20. InteractiveBiology October 15, 2011 at 8:36 pm #

    Glad to hear. All the best on your exam. Let me know how it went!

  21. veganthestephen October 17, 2011 at 9:15 pm #

    I like your series of videos but in this case, you really should explain how the Na+/K+ pump works in the pacemaker cell first to set up the potential gradient before the voltage sensitive K+ channels close while the Na+ is still pumped out. At this negative membrane potential, the Na+ starts to flow into the cell against the concentration gradient by diffusion, thus activating the potential of the cell which is the cause leading to -40mV where Ca+2 ions start flooding in.

  22. mariatico1 October 27, 2011 at 1:41 am #

    Funny channels ????

  23. zackboomer November 8, 2011 at 5:58 pm #

    @veganthestephen it flows against the concentration gradient by diffusion, or with the concentraion gradient?

  24. zackboomer November 8, 2011 at 5:58 pm #

    it flows against the concentration gradient by diffusion, or with the concentraion gradient?

  25. InteractiveBiology November 9, 2011 at 11:56 am #

    @zackboomer Unfortunately, Leslie is busy at the moment with more work to do for the site. He is unable to answer any questions. But, do stay tuned because more biology videos are coming very soon!

  26. InteractiveBiology November 9, 2011 at 11:56 am #

    Unfortunately, Leslie is busy at the moment with more work to do for the site. He is unable to answer any questions. But, do stay tuned because more biology videos are coming very soon!

  27. gullwings18 November 15, 2011 at 5:09 pm #

    great

  28. InteractiveBiology November 16, 2011 at 7:06 am #

    @gullwings18 Thank you! Stay tuned for more Biology videos coming very soon!

  29. InteractiveBiology November 16, 2011 at 7:06 am #

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

  30. aikatirah November 26, 2011 at 5:24 am #

    awesome video :) and you have a cute voice :)

  31. InteractiveBiology November 27, 2011 at 10:01 pm #

    @aikatirah Thank you! Please stay tuned. There will be more Biology videos coming very soon!

  32. InteractiveBiology November 27, 2011 at 10:01 pm #

    Thank you! Please stay tuned. There will be more Biology videos coming very soon!

  33. iainglasgow December 8, 2011 at 3:38 pm #

    @petercourt The Calcium-induced calcium release by is sequestered back into the SR. The remaining calcium is pumped out of the cell by the Sodium Calcium Exchanger. The sodium is then swapped back out for potassium.

  34. iainglasgow December 8, 2011 at 3:38 pm #

    The Calcium-induced calcium release by is sequestered back into the SR. The remaining calcium is pumped out of the cell by the Sodium Calcium Exchanger. The sodium is then swapped back out for potassium.

  35. iainglasgow December 8, 2011 at 3:38 pm #

    The Calcium-induced calcium release by is sequestered back into the SR. The remaining calcium is pumped out of the cell by the Sodium Calcium Exchanger. The sodium is then swapped back out for potassium.

  36. kingswood331 December 11, 2011 at 2:00 pm #

    All these videos are great. Please keep them coming. You are making
    learning a lot easier!

  37. kingswood331 December 11, 2011 at 2:00 pm #

    All these videos are great. Please keep them coming. You are making learning a lot easier!

  38. InteractiveBiology December 11, 2011 at 7:34 pm #

    @kingswood331 Oh yes, definitely! :) We will be uploading more videos soon so, please stay tuned!

  39. InteractiveBiology December 11, 2011 at 7:34 pm #

    Oh yes, definitely! :) We will be uploading more videos soon so, please stay tuned!

  40. MissEhouse December 14, 2011 at 9:13 pm #

    You are A-Mazing !! These videos help with almost every part of my
    physiology textbook.

  41. MissEhouse December 14, 2011 at 9:13 pm #

    You are A-Mazing !! These videos help with almost every part of my physiology textbook.

  42. InteractiveBiology December 15, 2011 at 1:16 pm #

    @MissEhouse Thank you! GLad that you seem to be finding value in the videos. Stay TUNED. WE have more Biology videos soon!

  43. InteractiveBiology December 15, 2011 at 1:16 pm #

    Thank you! GLad that you seem to be finding value in the videos. Stay TUNED. WE have more Biology videos soon!

  44. BadLemon625 December 19, 2011 at 3:33 pm #

    my turban has curry in it

  45. BadLemon625 December 19, 2011 at 8:33 pm #

    my turban has curry in it

  46. mlalramhluna December 20, 2011 at 2:18 pm #

    i dont know how u do it but it is clear that u hve a BIg heart….giving free lecture to others.Im a veterinarian and this helps me a lot to recollect the things which i have forgtn

  47. mlalramhluna December 20, 2011 at 7:18 pm #

    i dont know how u do it but it is clear that u hve a BIg heart….giving free lecture to others.Im a veterinarian and this helps me a lot to recollect the things which i have forgtn

  48. InteractiveBiology December 21, 2011 at 1:43 pm #

    @mlalramhluna Thank you. It’s what Leslie main goal is, to be able to share his knowledge to those who need them. Glad that you’re finding value in his videos. Stay tuned for more Biology fun!

  49. InteractiveBiology December 21, 2011 at 1:44 pm #

    @mlalramhluna Thank you. It’s what Leslie’s main goal is, to be able to share his knowledge to those who need them. Glad that you’re finding value in his videos. Stay tuned for more Biology fun!

  50. InteractiveBiology December 21, 2011 at 1:44 pm #

    Thank you. It’s what Leslie’s main goal is, to be able to share his knowledge to those who need them. Glad that you’re finding value in his videos. Stay tuned for more Biology fun!

  51. InteractiveBiology December 21, 2011 at 1:44 pm #

    Thank you. It’s what Leslie’s main goal is, to be able to share his knowledge to those who need them. Glad that you’re finding value in his videos. Stay tuned for more Biology fun!

  52. InteractiveBiology December 21, 2011 at 6:44 pm #

    Thank you. It’s what Leslie’s main goal is, to be able to share his knowledge to those who need them. Glad that you’re finding value in his videos. Stay tuned for more Biology fun!

  53. SHFOBA December 22, 2011 at 12:59 pm #

    The Calcium gate open before membrane reach threshold potential

    not till reach threshold potential..

  54. SHFOBA December 22, 2011 at 12:59 pm #

    The Calcium gate open before membrane reach threshold potential

    not till reach threshold potential..

  55. SHFOBA December 22, 2011 at 5:59 pm #

    The Calcium gate open before membrane reach threshold potential

    not till reach threshold potential..

  56. americandragonecko December 27, 2011 at 10:11 am #

    Awesome! This helped a lot!

  57. americandragonecko December 27, 2011 at 3:11 pm #

    Awesome! This helped a lot!

  58. XLordPikachuX January 21, 2012 at 2:46 pm #

    good stuff well said and it clears up a lot :)

  59. XLordPikachuX January 21, 2012 at 7:46 pm #

    good stuff well said and it clears up a lot :)

  60. tobyntoto128 January 22, 2012 at 12:51 pm #

    your videos are SOOOOOOOO helpful!!!!!! thank you SOOOOOOOOOOOO much!!!
    You are awesome.

  61. Eriance February 12, 2012 at 1:52 pm #

    @SHFOBA

    I believe this is the correct sequence of events:

    The T-type Calcium channels open after the funny channels closes, continuing depolarization. This brings the cell potential to the threshold which triggers the L-type calcium channel to spring open, allowing large amounts of Ca++, causing the action potential. I think he just merged both T and L type Ca++ channels together.

  62. Eriance February 12, 2012 at 1:52 pm #

    I believe this is the correct sequence of events:

    The T-type Calcium channels open after the funny channels closes, continuing depolarization. This brings the cell potential to the threshold which triggers the L-type calcium channel to spring open, allowing large amounts of Ca++, causing the action potential. I think he just merged both T and L type Ca++ channels together.

  63. Eriance February 12, 2012 at 6:52 pm #

    I believe this is the correct sequence of events:

    The T-type Calcium channels open after the funny channels closes, continuing depolarization. This brings the cell potential to the threshold which triggers the L-type calcium channel to spring open, allowing large amounts of Ca++, causing the action potential. I think he just merged both T and L type Ca++ channels together.

  64. nanoltw February 13, 2012 at 2:21 am #

    Shouldn’t there be a plateau phase? Seems like it is more of a skeletal muscle of action potential. Still very helpful though.

  65. nanoltw February 13, 2012 at 7:21 am #

    Shouldn’t there be a plateau phase? Seems like it is more of a skeletal muscle of action potential. Still very helpful though.

  66. fleetwoodfan12 February 14, 2012 at 12:27 pm #

    the 2 dislikes are my 2 physio profs

  67. fleetwoodfan12 February 14, 2012 at 5:27 pm #

    the 2 dislikes are my 2 physio profs

  68. CJCkarma February 28, 2012 at 11:38 am #

    Thank you. This really helps.. as I struggle with class lecture. This puts it all together for me. God Bless.

  69. NatiDuga February 28, 2012 at 11:45 am #

    Hi loved the video, is there any chance that this video is in spanish? I need it to present it in class, thanks!

  70. NatiDuga February 28, 2012 at 11:45 am #

    Hi loved the video, is there any chance that this video is in spanish? I need it to present it in class, thanks!

  71. CJCkarma February 28, 2012 at 4:38 pm #

    Thank you. This really helps.. as I struggle with class lecture. This puts it all together for me. God Bless.

  72. NatiDuga February 28, 2012 at 4:45 pm #

    Hi loved the video, is there any chance that this video is in spanish? I need it to present it in class, thanks!

  73. sherab March 28, 2012 at 7:02 pm #

    what is the cause the voltage-gated calcium channels open when we’ve reached the threshold?

  74. agreatgeat April 3, 2012 at 4:22 am #

    What returns those sodium back out of the cell? They never run out?

  75. agreatgeat April 3, 2012 at 8:22 am #

    What returns those sodium back out of the cell? They never run out?

  76. gina rimbey April 4, 2012 at 12:28 pm #

    Excellent! thank you.

  77. Anonymous April 4, 2012 at 4:28 pm #

    Excellent! thank you.

  78. gina rimbey April 4, 2012 at 4:28 pm #

    Excellent! thank you.

  79. abdinas3 April 8, 2012 at 5:46 pm #

    What about the bundle of His?

  80. abdinas3 April 8, 2012 at 9:46 pm #

    What about the bundle of His?

  81. marcman April 15, 2012 at 2:10 am #

    so the Na keeps building up inside the cell and K keeps coming out? Where does it come from?

  82. marcman April 15, 2012 at 6:10 am #

    so the Na keeps building up inside the cell and K keeps coming out? Where does it come from?

  83. digiconvalley April 21, 2012 at 8:06 pm #

    thankyou very very much

  84. digiconvalley April 22, 2012 at 12:06 am #

    thankyou very very much

  85. DanaBenDavid May 3, 2012 at 1:54 am #

    hannah and dana say thanks from CANADA!

  86. DanaBenDavid May 3, 2012 at 1:54 am #

    hannah and dana say thanks from CANADA!

  87. Jenny Chan May 6, 2012 at 1:11 am #

    just want to say thank you for making my life SO much easier ’cause I have an exam thats going to be 18 chapters…I don’t know how I will read it all. THANKS a lot :D

  88. Jenny Chan May 6, 2012 at 1:11 am #

    just want to say thank you for making my life SO much easier ’cause I have an exam thats going to be 18 chapters…I don’t know how I will read it all. THANKS a lot :D

  89. MrJordanio0825 May 16, 2012 at 6:02 pm #

    OMG!!! you PWN my physiology lecturer!!!

  90. MrJordanio0825 May 16, 2012 at 6:02 pm #

    OMG!!! you PWN my physiology lecturer!!!

  91. Amandagan000 May 27, 2012 at 7:55 am #

    you should come and teach in my university, one of my prfs sucks as

  92. Amandagan000 May 27, 2012 at 7:55 am #

    you should come and teach in my university, one of my prfs sucks as

  93. 1080portal May 28, 2012 at 4:42 pm #

    can u make money in biology?

  94. 1080portal May 28, 2012 at 4:42 pm #

    can u make money in biology?

  95. MajkeTiTvoje June 16, 2012 at 9:24 pm #

    i love the way you say node. NOAD

  96. MajkeTiTvoje June 16, 2012 at 9:24 pm #

    i love the way you say node. NOAD

  97. michaelbirkhead July 11, 2012 at 7:11 am #

    I really just need to verify/clarify something: The sodium ion continuously pumps into the cell and never has a period that it changes course and gets pumped out by Na/K pumps??
    This seems counter-intuitive – sodium can’t just enter the cells forever without putting a huge osmotic pressure on the cell and bursting it??? Can it?

  98. michaelbirkhead July 11, 2012 at 7:11 am #

    I really just need to verify/clarify something: The sodium ion continuously pumps into the cell and never has a period that it changes course and gets pumped out by Na/K pumps??
    This seems counter-intuitive – sodium can’t just enter the cells forever without putting a huge osmotic pressure on the cell and bursting it??? Can it?

  99. dbscout July 21, 2012 at 11:12 pm #

    Great vids. BS in bio, prepping for PA school, love these videos. Really great physio refreshers.

  100. dbscout July 21, 2012 at 11:12 pm #

    Great vids. BS in bio, prepping for PA school, love these videos. Really great physio refreshers.

  101. dbscout July 21, 2012 at 11:14 pm #

    @1080portal ever heard of physicians? They do pretty well for themselves.

  102. dbscout July 21, 2012 at 11:14 pm #

    @1080portal ever heard of physicians? They do pretty well for themselves.

  103. AQUANAM August 16, 2012 at 12:51 pm #

    Thank you so much :)

  104. hiranya1234 August 18, 2012 at 1:05 am #

    AMAZING! THANK YOU!

  105. koulaiyed September 23, 2012 at 1:23 am #

    WOW SO COOL
    THANKS!

  106. b05620 September 24, 2012 at 3:48 am #

    You save my life. I’m a working child and I end up missing a lot of class so these videos really really help me. Plus, you make things easy to understand and give a reason for everything which in turn makes it super easy to follow.

  107. DannyWiratama1987 September 24, 2012 at 5:11 pm #

    all these videos are great. thank you!

  108. Dreamynada October 21, 2012 at 6:38 pm #

    So amazing

  109. loverofbeats November 5, 2012 at 5:45 am #

    biology will never be fun…NEVER.

  110. vavila16 November 6, 2012 at 1:53 am #

    THANK YOU :) oh this helps me visually . I could not understand what contraction meant (i speak a different language) but seeing the first part now this really helps more than the text book and the lecture audio from my instructor

  111. Denisey411 November 6, 2012 at 7:25 am #

    wow u are amazing!!!!!!! than you from those of us who have bad teachers!!

  112. ejazkhanak47 November 7, 2012 at 8:04 pm #

    purkyne tissue he said purkingy fibres ?

  113. princeoz17 November 12, 2012 at 2:38 am #

    simple, concise and easy to understand. Very helpful, thank you Leslie

  114. loladify November 14, 2012 at 12:21 am #

    Very informative and to the point. Thank you

  115. msvang1988 November 21, 2012 at 4:07 am #

    You did a great job. Very very useful.

  116. yonpacx November 22, 2012 at 4:43 pm #

    tnx we need more like u thanks so muchhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh so clearrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr

  117. Rafaela Silva December 7, 2012 at 2:18 am #

    Very helpful!! Thank you!

  118. omega13594 December 7, 2012 at 7:46 am #

    A great vedio .. thanks sir (lub-dup:))

  119. Alejandra juarez December 11, 2012 at 8:50 pm #

    Great Video! Definitely helpful, thanks for posting

  120. Kristin Wells December 17, 2012 at 3:23 am #

    Amazing videos. Thank you so much. Making my classes so much easier to understand!

  121. TheGreatNerdHerd December 29, 2012 at 2:47 pm #

    thank you soo much for this heart series as i’m really bad at it as my mock proved :D

  122. HorseLvrArtwork January 6, 2013 at 11:43 pm #

    Thanks so much for putting this up. Appreciate it so much. Bless you.

  123. 080348629 January 12, 2013 at 1:48 pm #

    I like your vdo very much

  124. artem bluntzki January 24, 2013 at 3:52 am #

    Thank you. You just saved me a possible 40 minutes trying to figure out what my textbook is trying to tell me haha, 20 minutes of aimlessly staring into the pages and another 20 trying to read half latin/greek derived words. You display complex effects in simple terms and still manage to include all the crucial information.

  125. Kyle Danyluk February 1, 2013 at 10:15 pm #

    Thank you so much for this explanation. This has been tremendously helpful and I cannot thank you enough!

  126. Gabrielle C. February 19, 2013 at 4:54 pm #

    Thank you!! You made it so easy to understand!

  127. Marcela Martinez February 20, 2013 at 5:59 am #

    You are amazing!!!. Do you have any videos in which you explain the blood types and Rh factor?.

  128. SilvieOlgan February 21, 2013 at 5:31 pm #

    i have an exam tomorrow and this is great! :D

  129. MissMurderKMENDLTS March 6, 2013 at 12:07 am #

    it helped me alot thank you!!!!! :) u explain it very well :)

  130. Kawthar Abdullah March 8, 2013 at 1:27 am #

    Thx very much it’s really helpful

  131. HaneenA91 March 11, 2013 at 3:36 pm #

    perfect! thanks for this effort.

  132. amir dawood March 14, 2013 at 12:49 pm #

    thankxx

  133. Shanti Gurung March 18, 2013 at 2:53 am #

    lol

  134. Daniel O March 20, 2013 at 12:08 am #

    Very informative I love your videos, Keep them up

  135. steph10892 March 24, 2013 at 11:42 am #

    Another helpful video! Thank you!!

  136. greenlightwarfare . April 6, 2013 at 3:18 am #

    Doesn’t the influx of calcium followed by the opening of voltage gated K channels result in a plateau ? I’m really confused – please help!

  137. mwilso9123 April 12, 2013 at 1:46 am #

    This is like a skeletal muscles A.P?. Im a little confused my teacher was talking about funny channels, where does that come into the picture?

  138. Justin Forester April 15, 2013 at 9:32 am #

    There are two types of cardiac muscles: contractile muscle cells and autorhythmic muscle cells. Contractile cells make up 90% of muscle cells in the heart and autorhythmic cells make up 10% in the nodes. Autorhythmic muscle cells start the action potentials from the SA and AV nodes that disseminate into contractile cells causing them to contract. InteractiveBiology described the action potential of autorhythmic cells, you described contractile cells. Hope this helped :P

  139. chicmistique April 15, 2013 at 12:23 pm #

    thank you so much for posting these videos, they’re all very very helpful

  140. Tommy Moore April 24, 2013 at 9:54 pm #

    You are an awesome individual to take the time to put all these videos. And you make it so simple and easy to understand without getting lost. Thanks MUCH!!

  141. ZAR1411 April 28, 2013 at 5:43 pm #

    I just love how this particular person gives free lectures plus all the interactive are very easy for me to understand..keep up the good work leslie! You’re making everyone’s life easier :)

  142. ZAR1411 April 28, 2013 at 5:44 pm #

    yes that’s right.. because of the equilibrium

  143. WhatU GonnaDo April 30, 2013 at 12:42 am #

    I never understood this fully before, but you make things that much easier to understand. I can’t thank you enough!!!

  144. zaphod5589 May 2, 2013 at 7:50 am #

    where´s the funny channel ? xD

  145. Baqer Al-Saffar May 4, 2013 at 10:37 am #

    thank you so much that was a great help ^^

  146. dekalbwrestler May 21, 2013 at 9:15 pm #

    Leslie? Are you like a biology teacher or something? Maybe you just a nerd. Whatever the case thank you so much sir! I can understand you spoof much more than my cardiac teacher. She might be a super smart retired dr. But, there is something to say a out someone like you that can actually make you understand . I love you voice too. It’s soothing and intelligent sounding at the same time.

  147. EmTheGeeky June 9, 2013 at 10:05 am #

    Very helpful

  148. EmTheGeeky June 9, 2013 at 10:05 am #

    Thanks I think I finally understand this :)

  149. Gileiys680 June 14, 2013 at 5:07 pm #

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  150. ReinaDelAcordeon June 22, 2013 at 4:26 pm #

    I love your videos. Thank you for your help!

  151. pj johnson June 28, 2013 at 8:49 am #

    THANK GOD FOR YOU! VERY HELPFUL

  152. suraj ali June 30, 2013 at 4:25 pm #

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  153. suraj ali July 2, 2013 at 12:58 pm #

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  154. captainicehockey August 3, 2013 at 11:33 am #

    Thank you for your help. I’m a paramedic student and you broke down the depolarizing-repolarizing ion involvement very well for me to understand (we are currently beginning to analyze ECGs).

  155. Malibu95843 August 20, 2013 at 9:17 pm #

    Very well explained! Thank you so so much!

  156. zafarz8 September 5, 2013 at 6:28 am #

    why is potassium leaving the cell all the time,, doesnt potassium ever come back into the cell ?

  157. JJvideoman September 22, 2013 at 8:53 pm #

    when potassium leaves a cell not all of it goes. Its only a percentage change that causes the impulse to occur. So during stages in-between stimulation the potassium does move back in and replenish.

  158. Qiuyuan Yin September 30, 2013 at 2:16 am #

    totally helpful。。。thanks

  159. Akos Agyire October 6, 2013 at 5:35 pm #

    Can I borrow your brain for my exam tomorrow? Lol thanks for the review!

  160. Lex October 6, 2013 at 6:52 pm #

    Wow. That was so unbelievably clear. Thanks for making such a complicated concept fun and so easy to understand!

  161. Zaur Molotnikov October 7, 2013 at 4:04 pm #

    How can K+ only leave and never enter?

  162. lamkelvin19941117 October 23, 2013 at 10:34 am #

    Na+/K+pump allows K+ enter and Na+ leave

  163. lamkelvin19941117 October 23, 2013 at 10:34 am #

    Na+/K+pump allows K+ enter and Na+ leave

  164. Kathy Le October 31, 2013 at 11:03 pm #

    since there’s a higher concentration of K+ inside the membrane then outside, when K+ channels open, K+ will rush out because ions always move from higher concentrations to lower concentrations. The Na+/K+ pump then uses ATP to pump 2 K+ inside the membrane while pumping 3 Na+ outside so that a high concentration of K+ on the inside, and high concentration of Na+ on the outside will be maintained. This also makes the inside of the membrane negative again and return it to a resting potential.

  165. Aaron Bell November 8, 2013 at 1:57 pm #

    Amazing, in human physiology this semester so this is helpful.

  166. Eimear Short November 20, 2013 at 10:18 am #

    I was taught that there are no functional Sodium ion channels in pacemaker
    cells, is this wrong?

  167. MILU THOMSON May 6, 2014 at 2:37 pm #

    nice one!