Action potentials in cardiac myocytes | Circulatory system physiology | NCLEX-RN | Khan Academy
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- Опубликовано: 5 окт 2024
- See how muscle cells in the heart contract by allowing Calcium to flow inside and bringing along some positive charge with it! Rishi is a pediatric infectious disease physician and works at Khan Academy. Created by Rishi Desai.
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I'm not sure who the guy is that makes these videos, but he is incredible! Seriously, the guy is gifted! Very well done videos.
its me
This was really clarifying. Didn't mention the calcium induced calcium release, but still very helpful. Thank you so much!!
Excellent! I wish I watched this video, instead of trying to figure this out from the text for an hr :) Thank you!!!!
Slow (L-type) Calcium channels actually begin to open in phase 0 once the membrane potential reaches -30mV- -40mV. However, the effects aren't manifested until phase 2, as shown in the video, when the three types of K+ channels (I-to, I-k, and I-k1) slows down outward conduction speed to maintain the plateau.
Great question, check out the video on resetting the membrane potential which addresses your question.
Thanks a million
Been confused abt this stupid shit throughout my medical career...perfectly clear now...
hahah you are my idol dr. pallem
This comment made me laugh my head off! hahaha. Thanks :)
You never tried to find out in all your medical career!
😂😂this is funny!...just reading it after 3 years!!
lol!!!
I love you guys, but I have to say that I think there is something wrong in this video.
The voltage-gated Ca+2 channels don't "actually close just as suddenly as they opened", if they did there wouldn't be a flatline.
Actually their name is L-type Ca+2 channel, L for long lasting.
Unlike the Na+ channels of stage 0 which they actually close just as suddenly as they opened.
Unless I have misunderstood you, if that is I apologize.
You're totally right but i think he meant that they're closed entirely and not slowly.. if u get what i mean because there are some that take their time
Yep, the voltage-gated Ca+2 channels are slow gated channels, and because of the surge of Ca+2 it prolongs the contraction which is the "flat line" or the so-called Plateau
@@Sara-cj6gb yeah am new to this topic but wanna knw
How the cell gets this tremendous amount of potassium inside ?
Is there a K pump protein there ?
You're right. The L-type Ca2+ channels close down slowly during the end of phase 1 and during phase 2 (the plateau), making the membrane potential go down.
Voltage gated delayed rectifier K+ channels open up during the plateau phase, letting K+ ions leave the cell, contributing to repolarization. Simultaneously, Na-Ca exchangers trade 1 Ca2+ out of the cell for 3 Na+ in to the cell, slightly pushing the membrane potential upwards. These two almost balance each other out, but the net result is a slight repolarization during phase 2, which the video doesn't show very clearly.
The channels that actually DO close very quickly after activation are the transient outboard K+ channels which cause the rapid repolarization during phase 1 at +20 mV in the video.
Also, the first K+ channel that is drawn in the video is supposed to be the inward rectifier, and they close down completely slightly prior to phase 1, also contributing to the long plateau phase.
I understand that it's hard to convey every bit of information in only 12 minutes, but still. There are far more accurate videos out there.
You are right 100 percent
The potassium is moving inside through ATP dependant channel this channel is bringing 2 potassium inside in exchange for 3 sodium out using ATP the net result is resting potential of negative charge inside and positive charge outside
Helpful comment!
The exact membrane potential (+5mV vs. +15mV) will differ based on which cell we are looking at and its level of sympathetic stimulation (related to Calcium levels). Overall, this is the general shape of the action potential.
Thanks! I am enjoying making the videos. Have a great new year... =)
Thank you so much for explaining this in a way that is easy to understand. These videos have had a huge impact on my understanding and have greatly reduced my stress level!
Holy moly where was this video two hours ago in my studying. I am trying to study antiarrhythmic meds and felt like my eyes were crossing with understanding action potentials. You are a God send.
Great question. You're absolutely right...the membrane potential becomes more negative as potassium moves out of the cell and leaves behind an anion. Check out the membrane potential videos to see this in more detail. =)
Hello Rishi. Like the video's very much and am glad that you've joined the Khan Academy team. It's kinda strange not to hear Sal :) but you're doing a good job; the drawings and the speed is good. Thank you.
I know these videos are several years old now, but I just want to let you know how helpful they are! I have 13 of them pinned to my browser!
Rishi Desai, is my best teacher.
Learned a lot about Heart and how it functions.
Thank you so much sir.
I see a dedication and sincerity behind the video. Hope someday i too become somebody who could pass on the knowledge i earned from you.
Your proud student
I want to mention the role of Na-K ATPase pompe in the keeping of negative potentiel of cardiac myocytes ...so helpful explain..thank's
How does Calcium exit the cell? You explained how it enters in the beginning but how does it exit after the action potential to maintain balance?
The side notes on the y-axis of the graphic about calcium, sodium, and Potassium has helped to join many dots in my understanding of certain medications. Thanks a lot for also including that additional information in your explanation. It helped a lot.
This was great. A million times better than the teacher i med school
I only have an small constructive critic. I had explained how the ionic balance returns to place in stage 4, If I was completely new to this I would not be able to understand how with all the Na+ in and the K+ out the cell would be able to start a new potential:
Sorry to sort of necro the comments here but one thing I'd like to clarify: how does a positive ion (potassium) produce a negative membrane potential? Do you just mean that it is negative relative to sodium? I'm guessing that isn't the reason given your graph so if anyone can explain that would be great! Thanks :) great videos!
Rob Wagner because K+ ion diffuses out of the cell the inside of cell will become negative as positive ions have moved out
Rob Wagner also please watch my medical videos ruclips.net/video/ylP_e2fm0Wo/видео.html
I have two questions: What happened with all the calcium and Sodium that got inside the cell; 2) how does the cell recover K+ ? it seems to be loosing it all the time?
+1
In the cardiac myocyte cell the dominant ion, potassium leaves the cell resulting in a negative membrane potential of about - 90.(phase 4) As more positive ions such as sodium and calcium move into the cardiac myocytes cell the membrane potential becomes less negative resulting in a membrane potential of about -70.(phase 0) This change in membrane potential results in the opening of several voltage gated sodium channels within the membrane of the cell causing sodium to rush in. because of this massive influx of sodium moving into the cell the membrane potential becomes positive sitting at about +20 and results in the depolarization of the cardiac cell.(stage 1) As the membrane potential increases and approaches +20 the sodium voltage gated channels began to close and voltage gated potassium channels open allowing more potassium to move out of the cell decreasing the membrane potential two about +5. As the membrane potential slowly decreases and approaches 0 voltage gated calcium channels open allowing calcium to enter the cell, this alone would significantly increase the membrane potential of the cell however simultaneously potassium is leaving the cell which drives the membrane potential in the opposite direction. because these two opposing forces are happening simultaneously the membrane potential has no net change and remains flat at about +5.(stage 2) Overtime the voltage gated calcium channels begin to close while the voltage gated potassium channels remain open this results in the repolarization of the cardiac cell and a significant decrease in the membrane potential to about -90.(stage 4)
I'm in love with these explanations
great explanation..............Very helpful for Beginners like me.....keep doing the great job......Thanks.......P.S from INDIA :)
wow.... i am soo happy i never knew they hv vidoes of advanced medicine as well ....
This is a very clear and detailed video. Thanks for the concise and graphically detailed video. It served as a great revision video for me. Thanks alot
this is awesome thank you !!! finally understood this cardiac action potential
I can’t thank you enough
Organized, precise and simple
That is really really helpful.A million thanks to you!!!!!!!!!!!!!!!!!!!!!!
Great work! its a good and understandable describtion of the process. Thanks
Thank you so much for these videos! Your diagrams really help and suddenly anti-arrhythmic drugs make so much sense!!! Btw i was wondering did you leave out the Ca+ activated SR out of the diagram for simplicity?
Just a quick question, before the plateau, I understand that Ca2+ entering the cell would encourage the electric potential to become more positive, but how does potassium leaving the cell encourage the electric potential to become more negative? Since K+ is negatively charged, it seems like K+ entering the cell would create a more negative charge.... thank you!!
K+ is positively charged, and that's why it got a '+' sign.
Degang WU
Then why when a cell is in its resting state, it's charge is negative, and K+ is the predominate ion
Tracy Douglas You're right K+ is the predominate ion, but there are also anion, which are negatively charged. The membrane potential being negative just means that there are more anion than ion (here I assume each anion bears one negative charge for simplicity).
Degang WU
Thank you!!
That "-" before "-92 mV" refers to the resting potential the ion would "want" for the intracellular space. So the K+ ions, positively charged, kinda want to leave the cell... Making it even more negative than it currently is.
You should think about negative potential as a "difference in charge" - negative, because the interior is more negatively charged than the outside of the cell. Potential is not equal to charge.
Thanks for the crystal clear explanation on cardiac action potential!
Awesome, helped so much in my ECG course.
Also, 2 big points are missed. K+ is always leaking out. And the sodium potassium pumps in phase 3 use energy (ATP) to make the cell more negative. Hence in Vtach, the pumps fail and the cells constantly depolarize.
Imho the nuts and bolts of this entire process were not explained in this video, which nevertheless is an interesting summary.
Bro God bless your soul man. I hope God gives you a good gift someday
great vid, you explain things in a clear way
Amazing and very clear ..really Thank you very much
Very well articulated. Thank you
Hi, tks for the video.
Question: Why do "fast" sodium channel open at -70mV ? Does the threshold depend on the cell type or the channel type?
Because in a "normal" action potential, the RMP is -70mV and that would mean that "fast" sodium channels would be open - but they aren't.
this is really helpful. thanks a lot for the generous help.
Once again, you are a LIFESAVER! Thanks!
Very nice . such a nice explanation you gave
tnx a lot!!!!!! better than my teacher could explain it!
Great information and summary. Which gates are passive and which are energy consuming pumps? what are all the nuts and bolts of this entire process?
Thank you. You guys have been a huge help to me throughout my medical school journey.
Such an excellent lecturer!!!❤️
You're amazing! Thank you for making these videos. They really helped me a lot!
simply amazing.. thanks so much man! cheers!
thank you thank you!!!!!!!!! wonderful video!
hello, 52 year old trying to get this biology stuff down! Don't know what I would do without your generous help!
fantastic teaching mate. and amazingly neat... handwritting is a reflection of character and i can tell some characteristics from that handwritting :P
Great video, thanks!
Incredibly helpful!! 👏👏👏👏👏👏
THANK YOU FOR THIS!!!
Great video good quality teaching
perfect perfect perfect! thanks a lot
Thank you very much for the thorough explanation!
you're saving my life.
What causes calcium channels close after a while and why they don’t reopen after k channels opens more ?
very grateful for this! thanks for your time in educating! super helpful!
Kris Patrick please do watch my medical videos ruclips.net/video/ylP_e2fm0Wo/видео.html
It is very helpful!!!
this is amazing! very well explained. made me feel much better about the topic!
Thanks , This video is a great help
Awesome videos. Can you make a video on how epi and Acetylcholene affect the action potential in cardiac myocytes and pacemaker cells?
Crystal clear 💯
Great video.. Thanks for a clear explanation :)
great video ..
thanks alot ..
You're Awesome!!!!!!!!!❤️❤️
Superb. Thank you .
much needed. thank you
thank you so much this is such a great video you are an amazing teacher
I don't get how after the stage three ( where lots of K out and Na in ) we back to the stage four ? shouldn't be an activity for the Na-K pump to return the normal membrane status ?
thank you soooooooooooo much ..you just amazing
it's very helpful
thank you again🤗
A massive big thank you
I have a question; how does the membrane potential decrease at Phase 1 when potassium is leaving the cell? doesn't a cell's membrane potential be negative when only potassium was to be present in a cell, then how is it that once they leave the potential becomes negative? is it because of the presence of the anions when potassium leaves the cell?
What triggers the close of the calcium channels at +5mV? I understand that they're voltage gated but if no voltage change occurs due to potassium leaving simultaneously, ie the 'flat line', what causes the calcium channels to close off?
It's actually controlled by two mechanisms, the voltage (i guess there is a minimum of difference) and the second and most impotant, is the fact that there is a negative feedback caused by calcium levels in the cell itself, there is a calcium canal receptor in the smooth endoplasmatic reticulum, calcium levels are measured by it and when it's levels are high, it causes a very high velocity of internalization of calcium into the reticulum. So it's regulated by calcium level itself.
Although the purpose of this video isn't explicitly meant to cover QRS intervals, is it safe to say (4 -> 0 -> 1) is analogous to Q -> R, and (1 -> 2 -> 3 -> 4) is analogous to R -> T notation typically used in Biology? Just trying to bridge this application to EKGs. Thank you.
best explanation ever thanks a lot
really best of the best!!!
Great video! Would it be possible for you to describe the role of the inwardly rectifying potassium channel?
Thank you very much .. U r amazing
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Sorry
But you haven’t mentioned the NA K ATPASE PUMP at the end of the cycle
Awesome video!
Isnt there a pump we should be talking about that restores the ions to the initial state ?
na k pump
sodium potassium pump maintin original position of ions using atp.
Question: is K+ potassium always leaking out of the cell?
Explained perfectly
At what stage does contraction happen? And how does Acetylcholine play a role in cardiac muscle action potentials?
Amazing, thank you!
How does this work in terms of propagation of action potential into down into the t-tubule? Thank you.
wow i finally understand!!
very nice... a big thumbs up
thanks a lot you filled up mu gaps
PERFECTLY EXPLAINED! But is an action potential the reason you get an influx of Ca2+ ions, just like a in a neurone?
The influx of calcium causes the sarcoplastic reticulum to ALSO release it's calcium, and this causes the cardiac muscle to stroke (or pump). That is, the voltage-gated calcium channel opens at phase 2, and the increase in intracellular calcium signals the sarcoplasmic reticulum to release calcium.
Thank you!
excellent!
what happens to the Ca2+ and Na+ during the depolarization phase? do they rush out again? where do they go once their gates have of closed on them?
Hi,
I have a textbook which makes reference to a transient outward potassium current, delayed rectifier potassium current and inward rectifier current. The first appears to be balanced by the inflowing calcium during the plateau phase; the second appears to repolarise the membrane; and the third has its role in establishing and maintaining the resting potential. Thus the first two involve an outward flow. Are these voltage-gated? Is the terminology important?
@7:42 I feel dumb asking this but how does potassium leaving the cell make the cell repolarize?