Cardiac Conduction & Cardiac Action Potentials

[@dianaefrost]

This video was great because it not only compared and contrasted cardiac verses skeletal muscles, but it reviewed action potentials in general and explained the difference between a cardiocyte receiving the action potential from the pace maker cells. I was confused when you said "something" generates the action potential, but other than that, great job!!!!

[@rommeljadaan6975]

I love your explanations Andrew. Thanx a billion. I use your concepts to educate our emergency physicians and paramedics in North of Italy. Clear, Valid , simple and universal. Thank you. Dr. Rommel Jadaan

[@HealthEdSolutions]

Thank you for the feedback Dr. Rommel Jadaan. Glad you found it helpful!

[@steveneiger5284]

Andrew, I like your videos. One fun point. There are v-s Na channels expressed, but since the Vm only gets to -60mv, the channels stay inactivated. remember the inactivation gate of the channel only resets when Vm returns to around -70 mv. Steve

[@charlesclintonmd]

Nice vid, just wanted to add minute correction and info. Minute 7: the delay is specifically the PR SEGMENT, PR interval includes both Atrial depolarization and delay... PR interval shortening (less than 0.12s is seen in "preexciting syndromes" as Wolff parkinson white and long ganong levine)

[@trevorstone1869]

haha, i was just about to leave a comment pointing that out too, otherwise, nice video Andrew, makes a nice change to sit and listen to this rather than bury your head in a textbook. Cheers

[@HealthEdSolutions]

Thanks Trevor for the kind words!

[@Lbetter425330]

Can you go over the EKG and how it relates to depolarization and depolarization of the atria and ventricles?

[@carriemann9426]

Great video. Just want to clarify...with a cardiac myocyte is Phase 1 fast K+ efflux or fast Na+ efflux? @ around 15:45 you say phase 1 is fast Na+ efflux but written on the screen is Fast K+ efflux.

[@HealthEdSolutions]

Thanks for watching and the input!

[@Dheejks]

You said you can not think of anything that would decrease the length of the PR interval; but what about accessory pathways e.g. Bundle of Kent in Wolf-Parkinson-White syndrome?

[@HealthEdSolutions]

Thank you for the feedback and input!

[@Kim-yu8js]

Thank you for all your videos! If you close K+ leak channels, does that hypopolarize the cell because the cell becomes more negative? That will increase excitability, but what does it do to the force of contraction?

[@HealthEdSolutions]

Thanks so much for watching!

[@carriemann9426]

OK, that makes sense. Thank you clarifying!

[@HealthEdSolutions]

Thanks for the support Carrie!

[@kumartunesh1284]

superb lecture.... well done andrew

[@HealthEdSolutions]

Appreciate the kind words Kumar!

[@NieceyWeesey]

What did you mean when you said 'AV cells lack actin and myosin'? I thought they did have it otherwise they wouldn't be able to contract...I'm confused

[@NieceyWeesey]

***** Thank you. I get it. I accidently muddled the two types of cells :) great vid!

[@HealthEdSolutions]

Thanks for watching!

[@HealthEdSolutions]

Absolutely!

[@edwardpinder5634]

Thanks bro but I think you have purkinje fibers and bundle branches muddled up the wrong way round.

[@HealthEdSolutions]

Thanks for the feedback!

[@mandyads]

Hey Andrew, for now (since you might not have time to re-upload the video with edits, etc.), you should simply put the changes in the description box. This video was actually given to my animal physiology class by my professor. I would hate to get a question wrong on our exam because I learned it wrong. I don't even know what "mistakes" everyone is talking about. Regardless... Nice work. Thank you!

[@mandyads]

***** Awesome, thank you!

[@HealthEdSolutions]

Thanks for the feedback Dani!

[@HealthEdSolutions]

Thank you:)

[@liamohalloran4197]

I thought there was a potassium rectifier channel at the end of the AP also i thought there was something about decreased permeability to K+ during the plateau phase that worked with Ca+ channels to enable the plateau? Perhaps you could explain, i'd greatly appreciate it, hard to wrap my head around this stuff!

[@HealthEdSolutions]

Thanks so much for your inquiry. We have passed this question on to our medical review team. Thanks again for watching!

[@xBassel92x]

Cardiac dysrhythmia called premature cardiac contraction ( with includes syndromes like WPW, CLC, LGL) causes a shortening in P-R interval to less than 0,120 mc ...

[@HealthEdSolutions]

Thanks for the feedback Bassel and thanks for watching!

[@shellygrl62489]

AMAZING!!!

[@HealthEdSolutions]

Thanks so much. Glad you enjoyed the lesson!

[@docinternalmedicine]

nice video... good intetion, sum of this stuff i was really not fundamentally clear about, really thank u. But u need to fix the per second bit... coz i think students who are a bit clueless might end up learning it all wrong.it is a serious mistake since u keep repeating it too.

[@arch3rror]

for the pacemaker cells, their lowest membrane potential tends to be around -60 not -90, and there is no role of fast na channels unlike what you mentioned, and there is no plateau phase either. andrew, you have the right intentions but this video is far too long and incorrect. please correct the errors.

[@Kim-yu8js]

oops, I meant intracellular becomes less negative.

[@HealthEdSolutions]

Thank you!

[@nourahalrabah9263]

How does an action potential every 10 seconds cause a heart rate of 60bpm? Wouldn't that be 6?

[@HealthEdSolutions]

Thanks so much for your inquiry. We have passed this question on to our medical review team. Thanks again for watching!

[@anhadjvbft]

sir.....it should be 60-80beats/min not per sec as u mentioned ....also 50 beats/min n 25 beas/min

[@ramzeschavez]

can anybody tell me what software is that!!!! (drawing one)

[@HealthEdSolutions]

Thanks for your inquiry. The whiteboard lessons are created using a Wacom Bamboo tablet. Thanks for watching!

[@nickmahy4125]

Regarding pacemaker cells, should be beats per minute not per second:-)

[@HealthEdSolutions]

Thanks for taking the time to comment and watch. Appreciate the input!

[@cks7298]

Nice video

[@HealthEdSolutions]

Keep watching, we appreciate the support!

[@katmcgrath3831]

A lot of very basic mistakes, you should add a disclaimer or addendum of some kind

[@HealthEdSolutions]

Thanks for the feedback Kat!

[@wajdiahmed9149]

it is perfect

[@shanmugalingamshrikharan2056]

Firstly I must thank you for the videos. But I should also point certain omissions related to action potentials. First you mentioned in a nerve the two phases Phase 0 - fast Na influx Phase 1 - fast K efflux so restore membrane potential. I am afraid this should NOT be all. What about restoring ionic normalcy? Na has come in from outside and potassium had leaked outside. Aren’t they too should be restored? Before the next action potential Na should get out of the cell and K should get into the cell. You have not mentioned this. Otherwise with each and every action potential the nerve cell will become excess of Na and depleted of K and in a short time after birth nerve will stop functioning. Similar story in a cardiac conduction system you have not mentioned anything how ionic normalcy is restored. With each cardiac beat Na level increases and K decreases within the conducting cells and we have to die in a few days after birth! I hope you have caught my point

[@mattkaka6657]

In this case it would be the Na/K pump restoring the balance for the skeletal muscle. In terms of cardiac muscle I assume the same but what happens to the calcium?

[@shanmugalingamshrikharan2056]

Matt Kaka Thanks for your response. Not only electrical gradient across the membrane should be restored before the next action potential but also the ionic concentration inside and outside the muscle cell should be restored before the next action potential. Na had leaked inside and it should be pumped out of the cell, and so with Ca. K had gone out of the cells to the ECF and they should be brought back into the cells. This should happen before the next action potential. This is not mentioned anywhere. I have watched many videos uploaded on the same topic and no one have mentioned this point. I do not know much of this physiology. But this is simple common sense and not rocket science. It cannot be the world came to know only after I mentioned this in KZbin!!! You cannot assume that somehow Na and Ca will get pumped out and K will get pumped in. It is so important it should be mentioned. Again it is my common sense. Otherwise as I mentioned, with each cardiac cycle Na and Ca concentration within the cell will increase and K concentration will get depleted and there will be a stage soon no K left in the cell for the repolarization and heart will stop! This should happen within the first day of birth and no human or animal can survive more than a single day and will die. Obviously something is wrong! Certainly ionic normalcy is and should take place before the next action potential. It is not something trivial to be left out in a description of the physiology of cardiac muscle contraction. Andrew Wolf (as well as all others) has not mentioned this. I hope Andrew catches my comments and responds.

[@shanmugalingamshrikharan2056]

***** Thanks for the response. I should thank you for your videos and the effort you put to create them. So you are saying since only minute numbers of molecules are involved and so restoration of ionic concentrations are not important and do not take place. This is what I can interpret from your comment. Then this should have been mentioned in your video as it is a very important information. This is something sticking out. Anyone will wonder what happens to the Na and Ca which entered the cell and the potassium that leaked out. Now you have said, it is minute so body will not bother. This should have been mentioned. Don’t you agree with me using simple common sense, certainly over the time whether it is adjacent to the cell membrane or within the cell, if the Na and Ca does not get pumped out they are going to get accumulated and potassium if not pump back in it will get depleted. Over the time the minute numbers will become significant. Man lives more than 70 years and this minute amounts will become significant long before he reaches 70. I think restoration of ionic balance in and out of the cell should be a phase. I think body accounts for every single ion and that is how milieu interior is maintained. Body is not going to say it is only minute amount and we will leave it. I have said all I have to say. I will not discuss in this particular point again. Thanks again for the explanation. Please continue to post videos and they are helpful.

[@DJMichael_95]

awesome andrew, have a look at my channel, let me know what you think, i've just started

[@Arimatt1]

Nice video... but I'm sooo tired of waiting for u to come up with words... talk faster!

[@HealthEdSolutions]

Thanks for the feedback!