At what point does the sodium and calcium leave and at what point does the potassium enter? This example model would lead to a swelling of the cells with Na and Ca ions and the cell would be depleted of K within a few cycles...
These videos are so wonderful as a study aid for medical school! I can always come back to these to get down to the most basic concepts and extrapolate them to things such as anti-arrhythmic pharmacology. THANK YOU SO MUCH!
I studied biology in undergrad; I did well on the MCAT; I am a second year in med school.... and this was the best explanation of how action potentials work I've ever seen. I can't even begin to thank KhanA for their work.
There's a reason why you joined the Khanacademy team; you fit right into Sal's "intuitive" (not to mention that you sound a bit like him) way of teaching. Thanks to all of you guys for broadening the library.
I have never been able to grasp the concept of action potentials within the cardiac muscle cell no matter which professor for A&P 1 or 2 trying to explain it but this video with the diagrams and everything have single handedly saved my life lol
0 stage (action potential) is because of Ca+ coming in(,not bc Na+ coming In as in cardiac myocyte) stage 1 and2 is not present in pacemaker cell because pacemaker do not have platue stage 3 is repolarization because K+ out leaving -ve inside stage 4 is activation of If Na+channel (because of repolarization by K+ out ward) now this Na+ wil depolarize to threshold (not action potential) to open Ca+ channel these Ca+ entry (or stage one again ) is action potentional (during whole phase ions are actively transporated to their orignal concentratioout and inside by Na K atpase pump and contratranprrt
first of all, what cause the action potential is ( sodium and calcium ) , first there is ( slow sodium channels ) that make the potential reaches " threshold" and after that a channels call ( sodium-calcium channels ) activated , thus causing action potential ( both the sodium and calcium ) ( source ; Guyton, Textbook of physiology chapter 10, 117)
Of course you don't. I don't either. It's not necessarily that your lecturers are bad or unskilled - it's just that khan academy team is one of a damn kind and it is an absolute blessing for us to have access to them
Thank you!!!!! I LOVE khan academy videos! My sister-in-law introduced them to me recently because I was getting rusty on a few things. They're so easy to understand in comparison to how I learned info in nursing school. Education is a big part of a nurse's career. With these videos, I feel I can educate my patients better.
THANK YOU for explaining all the math!!! Most teachers don’t even care about it or to explain it, now the numbers make more sense now and it’s easier to grasp the concept
the 4, 0, 3 numbering system is used because in 'non pacemakercells' the 0 represents Depolarisation and the the 3 represents repolarisation and those two numbers represent the same events in 'pacemaker cells'. Thats why they chose those specific numbers.
This video, as well as the one on cardiac myocytes have been very helpful to me. However, in my Anatomy & Physiology course there are some pieces to the pacemaker cell action potential that were not in this video which I feel would be important to add. Terms: Funny Channels T-type channels L-type channels Early drift Late drift These pieces were shown in the video but not named.
So, there is a difference between action potentials in pacemaker cells and action potentials in cardiac myocytes?? Or was it just an example to use different ions coming into or going out the cells?
Thank you very much! You have a knack for explaining things well. My only comment would be on your use of the word "salt" synonymously with sodium. Chemically speaking salt would mean an anion and cation, and if you were using it to mean "table salt" it would include chloride as well, not just sodium.
Thank you so much for the videos. You make complex materials so much easier to understand and explain things which are often missing from textbooks. I also love your voice.
i just wanna say how great you are my god!! So wondrous. God created for us these cells and with high accuracy !! nobody can create these cells just a god
Really good, doing my MBBS and our cardio lecturer is shocking. Would you be able to explain next time how calcium exits the cell? is the potassium sodium pump the slow "leaky" sodium channels that trigger threshold or are they different?
I don't understand how this can work. If Na is flowing into the cell and then Ca flows into the cell and K flows out of the cell. All the electrolytes need to go back. K needs to get back in the cell, Na and Ca needs to move back out of the cell. The switching back of all the electrolytes is not talked about. How can we just start over if all the electrolytes are not in the correct area?
Basically there are two kinds of K+ channels: rapid delayed rectifiers (IKr) and inwardly rectifying (IK1). IKr is the primary channel, so there's a net outward, positive current (making the inside of the cell more negative), and this is repolarization. IKr closes when the membrane potential is about -85 to -90 mV. BUT the IK1 keeps open throughout phase 4 (allowing K+ to return inside). The Na/Ca exchanger and Na/K pump also help to restore ion concentrations. So like, the Na/K pump is an ATPase that pumps both ions against their concentration gradient, which means it'll pump Na+ out & K+ in, thus returning everything to how it was!
The Na+ and K+ ions are "replaced" by Na/K ATP-ase which pumps 2 K+ ions into the cell for every 3 Na+ ions out of the cell and re-establishes these ion gradients. The Ca+ ions are also pumped out of the cell in a similar fashion. Bottom line- there are many ion channels and other membrane proteins at work. This is just a simplification of how "action potentials" work in the nodal cells.
Can someone explain to me why during phase 3, if K is leaving the cell how does the cell's mV become more negative. If K has a - charge than in my mind the cell would increase it's + charge. Thank you for anyone's help. Thank you for the video as well!
The action potentials in the SA and AV nodes are largely due to Ca++, with no contribution by Na+ influx (Ganong's Review of Medical Physiology, Twenty-Third Edition Chapter 30 -Origin of the Heartbeat & the Electrical Activity of the Heart. Sub topic- Pacemaker potentials.) Please explain this
Sodium ions cause the pacemaker current in cardiac cells, which causes the membrane potential to change from -60 mV to reach the threshold potential of -40 mV. This slow influx of sodium ions through the hyperpolarization-activated cyclic nucleotide-gated channel (HCN channel) generates the pacemaker potential. The slope of phase four determines heart rate and is different for pacemaker cells in different regions. For example, SA node pacemaker cells depolarize at a rate of 60 to 100 per minute, while the AV node at 40 to 60 per minute.
Phase-0: Slow ca channnels open; calcium influx. "Resting K channels close due to this depolarization. Phase 3: Repolarization due to calcium channels closing and k channels opening which allows unopposed k efflux. Phase 4: "Diastolic-Depolarization (automaticity). why? Slow closure of K channels and sodium slowly leaking into the cell (SLOW) (imp);catecholoamine or b1 agonists act here by increasing "SODIUM- INFLUX) leading the cell become more positive until it reaches a threshold.
When the membrane potential reaches -45mV, the T type calcium channels open, and when the membrane potential reaches -30mV, the L type calcium channels open, and finally when the cell becomes positively charged, the voltage-gated potassium channels open and a repolarization occurs.
What about the Bachmann's bundle and the internodal tracks? are they made up of pacemaker cells? If so, does that mean that those cells could fire spontaneous action potentials if the SA node, AV node and purkinje systems are not working? if they're not made out of pacemaker cells, then are they just made out of normal cardiac muscle cells?
This is what I do for a living. ECG Technician and Paramedic. I thought you were going to be talking about pacemakers that people have implanted in them when their hearts fail to work right.
en.wikipedia.org/wiki/Cardiac_action_potential#Phase_4 I had the same question. Apparently, it's due to both. (Along with a decrease of Potassium exiting). "This pacemaker potential is predominantly due to increased inward current of sodium (Na+) through voltage-dependent channels, but also an increased inward calcium current and a slowly decreasing potassium outward current." I hope it helps :)
You haven't mentioned how and when Sodium and Calcium ions leaves the cell again, and how Potassium ions enter the cell again. But thank you for the video! much clearer than my lecture notes.
ELFCloudGamer I found a link that MIGHT help you understand, but You Tube is user hostile about people putting links in their comments, so I can't put it here. I couldn't find it on Google. I'm not that Internet literate. I wish You Tube didn't have a bee in their bonnets about putting web site links in their comments section. But for the record, the site I visited claimed not to fully understand how all of it happens.
The entirety of the action potential (phase 0) is due to the Ca2+ ions. Na+ ions must influx in order for the membrane to reach the threshold, which then leads to the action potential. Just a misunderstanding of wording. :)
some of the text book says that the Na channel closes after the rapid depolarization, and the beginning of the re-polarization. What's your opinion on it?
I'm glad that you find the videos helpful! There are many more to come...
Absolutely brilliant. I have subscribed!
Please Overdrive suppression explain
At what point does the sodium and calcium leave and at what point does the potassium enter? This example model would lead to a swelling of the cells with Na and Ca ions and the cell would be depleted of K within a few cycles...
This is a very simplified version for non med people
@@life42theuniverseThis is introductory. Read further and do some research.
These videos are so wonderful as a study aid for medical school! I can always come back to these to get down to the most basic concepts and extrapolate them to things such as anti-arrhythmic pharmacology. THANK YOU SO MUCH!
cbcCarissa Wilkins
I'm doing exactly the same lmao
Doing it right now
I studied biology in undergrad; I did well on the MCAT; I am a second year in med school.... and this was the best explanation of how action potentials work I've ever seen. I can't even begin to thank KhanA for their work.
Potassium reenters the cells by the Na/K pump which is ALWAYS working to keep the potassium levels nice and high in the cells.
There's a reason why you joined the Khanacademy team; you fit right into Sal's "intuitive" (not to mention that you sound a bit like him) way of teaching. Thanks to all of you guys for broadening the library.
I like this guy that helps Khan. His voice, straight forward, nice. easy to learn
These really are the most educational videos you're going to find on youtube, great work!
K. Kl l
I have never been able to grasp the concept of action potentials within the cardiac muscle cell no matter which professor for A&P 1 or 2 trying to explain it but this video with the diagrams and everything have single handedly saved my life lol
0 stage (action potential) is because of Ca+ coming in(,not bc Na+ coming In as in cardiac myocyte)
stage 1 and2 is not present in pacemaker cell because pacemaker do not have platue
stage 3 is repolarization because K+ out leaving -ve inside
stage 4 is activation of If Na+channel (because of repolarization by K+ out ward)
now this Na+ wil depolarize to threshold (not action potential) to open Ca+ channel these Ca+ entry (or stage one again ) is action potentional
(during whole phase ions are actively transporated to their orignal concentratioout and inside by Na K atpase pump and contratranprrt
first of all, what cause the action potential is ( sodium and calcium ) , first there is ( slow sodium channels ) that make the potential reaches " threshold" and after that a channels call ( sodium-calcium channels ) activated , thus causing action potential ( both the sodium and calcium ) ( source ; Guyton, Textbook of physiology chapter 10, 117)
i studied this for 6 years and still can't understand this shit
If only I had lectures like this! Easy to follow. Thank you for posting!
Of course you don't. I don't either. It's not necessarily that your lecturers are bad or unskilled - it's just that khan academy team is one of a damn kind and it is an absolute blessing for us to have access to them
Thank you!!!!! I LOVE khan academy videos! My sister-in-law introduced them to me recently because I was getting rusty on a few things. They're so easy to understand in comparison to how I learned info in nursing school. Education is a big part of a nurse's career. With these videos, I feel I can educate my patients better.
This looked complicated and sounded complicated, but sir you made it simple and now I understand it. So I thank you for been such a good teacher :)
Good job!!! I wish our teachers would explain things like you. Than I would start going to their lectures...
THANK YOU for explaining all the math!!! Most teachers don’t even care about it or to explain it, now the numbers make more sense now and it’s easier to grasp the concept
the 4, 0, 3 numbering system is used because in 'non pacemakercells' the 0 represents Depolarisation and the the 3 represents repolarisation and those two numbers represent the same events in 'pacemaker cells'. Thats why they chose those specific numbers.
This video, as well as the one on cardiac myocytes have been very helpful to me. However, in my Anatomy & Physiology course there are some pieces to the pacemaker cell action potential that were not in this video which I feel would be important to add. Terms:
Funny Channels
T-type channels
L-type channels
Early drift
Late drift
These pieces were shown in the video but not named.
+Brittany Montero really helpful also for me
thank you! I have a midterm in 2 days and you truly explain better than my prof!
So, there is a difference between action potentials in pacemaker cells and action potentials in cardiac myocytes?? Or was it just an example to use different ions coming into or going out the cells?
Gülay Yalcin there's a difference. Pacemaker cells are special modified cardiac myocytes.
Gülay Yalcin what I've read that is pacemaker cells unlike cardiac myocytes do not need any stimuli to generate Action potential.
They are different. There´s another video of Khan academy about the pacemaker action potential, check it out.
Khan Academy for medical school! I love it! Thanks for the awesome work!!
Loving this series of videos!!!!!!!
Wow. What a wonderful explanation! Thank you so much!
Thank you very much! You have a knack for explaining things well.
My only comment would be on your use of the word "salt" synonymously with sodium. Chemically speaking salt would mean an anion and cation, and if you were using it to mean "table salt" it would include chloride as well, not just sodium.
Thank you so much for the videos. You make complex materials so much easier to understand and explain things which are often missing from textbooks. I also love your voice.
This guy is intelligent and very knowledgable (and interesting), but long on hand waving and short on complete, logical explanations.
Awesome way of teaching 😍😍
After so many years, i understand it now ! Thank u very much
i just wanna say how great you are my god!! So wondrous. God created for us these cells and with high accuracy !! nobody can create these cells just a god
God bless the internet, thank you
amazing video. thank you very much
Really good, doing my MBBS and our cardio lecturer is shocking. Would you be able to explain next time how calcium exits the cell? is the potassium sodium pump the slow "leaky" sodium channels that trigger threshold or are they different?
So clear thank you!
thanks a lot for these videos as I learned about how , the human heart works.....thnks
I love these lecture or videos that you post thank you and easy to understand
Thank you so much, for this video! It helped me a lot to understand cardiac electrophysiology !
amazing video. English is my second language but you really explain this so simply!
the world need more heroes..... who have gifts in explaning. the XPLAN-MAN!!!!
It makes TOTAL sense to me. I know exactly where those are.
The purkinje fibers are on both sides of the heart in the middle - on the septum, the wall that separates the right side of the heart from the left.
Amazing! 👏
@3:00, where are you getting the numbers from?
Very good video. Keep making. Love from india🇮🇳🇮🇳🇮🇳🇮🇳
You vids are sooo helpful. Im studying at university and think the vids are a reallu gd was to get to grasps withbthe basics. Thank you
I really admire it.its awfully good
Fantastic revision for IBHRE!! Thank you!
You make this less confusing, thank you!
I loved loved this...this is absolutely appropriate and more
the colors are so pretty
I don't understand how this can work. If Na is flowing into the cell and then Ca flows into the cell and K flows out of the cell. All the electrolytes need to go back. K needs to get back in the cell, Na and Ca needs to move back out of the cell. The switching back of all the electrolytes is not talked about. How can we just start over if all the electrolytes are not in the correct area?
excatly... it explains only one cycle
Basically there are two kinds of K+ channels: rapid delayed rectifiers (IKr) and inwardly rectifying (IK1). IKr is the primary channel, so there's a net outward, positive current (making the inside of the cell more negative), and this is repolarization. IKr closes when the membrane potential is about -85 to -90 mV.
BUT the IK1 keeps open throughout phase 4 (allowing K+ to return inside).
The Na/Ca exchanger and Na/K pump also help to restore ion concentrations. So like, the Na/K pump is an ATPase that pumps both ions against their concentration gradient, which means it'll pump Na+ out & K+ in, thus returning everything to how it was!
what about Na?
The Na+ and K+ ions are "replaced" by Na/K ATP-ase which pumps 2 K+ ions into the cell for every 3 Na+ ions out of the cell and re-establishes these ion gradients. The Ca+ ions are also pumped out of the cell in a similar fashion. Bottom line- there are many ion channels and other membrane proteins at work. This is just a simplification of how "action potentials" work in the nodal cells.
Can someone explain to me why during phase 3, if K is leaving the cell how does the cell's mV become more negative. If K has a - charge than in my mind the cell would increase it's + charge. Thank you for anyone's help. Thank you for the video as well!
because K+ is effluxing
Literally understood it for the 1st time
Thanks, I understand this so much better
Keep up the good work !!!
THANK YOU!!! Now I get it. You make this very easy to understand :)
This is excellent.
So, does this mean that pacemaker cells and cardiomyocytes don't have refractory periods? or time for channels to "recover"?
thank you ^^ I really needed this to understand :)
Wonderful explanation. Thank you for your efforts.
The action potentials in the SA and AV nodes are largely due to Ca++, with no contribution by Na+ influx
(Ganong's Review of Medical Physiology, Twenty-Third Edition
Chapter 30 -Origin of the Heartbeat & the Electrical Activity of the Heart. Sub topic- Pacemaker potentials.)
Please explain this
Sodium ions cause the pacemaker current in cardiac cells, which causes the membrane potential to change from -60 mV to reach the threshold potential of -40 mV. This slow influx of sodium ions through the hyperpolarization-activated cyclic nucleotide-gated channel (HCN channel) generates the pacemaker potential. The slope of phase four determines heart rate and is different for pacemaker cells in different regions. For example, SA node pacemaker cells depolarize at a rate of 60 to 100 per minute, while the AV node at 40 to 60 per minute.
Phase-0: Slow ca channnels open; calcium influx. "Resting K channels close due to this depolarization.
Phase 3: Repolarization due to calcium channels closing and k channels opening which allows unopposed k efflux.
Phase 4: "Diastolic-Depolarization (automaticity). why? Slow closure of K channels and sodium slowly leaking into the cell (SLOW) (imp);catecholoamine or b1 agonists act here by increasing "SODIUM- INFLUX) leading the cell become more positive until it reaches a threshold.
You guys are awesome! Thanks :)
When the membrane potential reaches -45mV, the T type calcium channels open, and when the membrane potential reaches -30mV, the L type calcium channels open, and finally when the cell becomes positively charged, the voltage-gated potassium channels open and a repolarization occurs.
What about the Bachmann's bundle and the internodal tracks? are they made up of pacemaker cells? If so, does that mean that those cells could fire spontaneous action potentials if the SA node, AV node and purkinje systems are not working? if they're not made out of pacemaker cells, then are they just made out of normal cardiac muscle cells?
thank you. It was really helpful.
simple and very helpful! amazing.. thank you
you guys are the best
Thank you 🙏🏻 thank you thank you sooooo much you saved me ,,, I was lost
Thank you so so much! This is very clear!!!
A great lecture. Thank you so much!
thank you this is incredible!!!!!
can you make a video explaining (If) channels or funny current channels
this guy. is amazing.
Amazing knowledge
thank you, excellent demonistration
great!
Thanks man, really good explanation!
Amazing teaching, thanks for this
Thank you sir ❤
Brilliant!
thank you a lot , so clear!
So wonderful so amazing & so lovely
Khan helping me even in med school
This is what I do for a living. ECG Technician and Paramedic.
I thought you were going to be talking about pacemakers that people have implanted in them when their hearts fail to work right.
Kind of like a redstone clock
K has a + charge. Since K+ is positive then the mV is going to become more - to attract the K+ so it will stay in the cell. Hope this helps.
THANK YOU!
Amazing video! But just to make sure, the Na+ voltage-gated channels are always open no matter what the other channels are doing, right?
u r the best!!! thank uuuuuuu a lot
Very useful video
is the automaticity character due to inflow of Na as you said in the video or slow inward Ca currents ?
en.wikipedia.org/wiki/Cardiac_action_potential#Phase_4
I had the same question.
Apparently, it's due to both. (Along with a decrease of Potassium exiting).
"This pacemaker potential is predominantly due to increased inward current of sodium (Na+) through voltage-dependent channels, but also an increased inward calcium current and a slowly decreasing potassium outward current."
I hope it helps :)
I am really really appreciate it thank you so much!!
thank youuu ✨
Very helpful
You haven't mentioned how and when Sodium and Calcium ions leaves the cell again, and how Potassium ions enter the cell again. But thank you for the video! much clearer than my lecture notes.
They do it through osmosis for one, but that's the only one I remember.
I'm an ECG Technician. It gets way more complicated than this video actually.
Vicki Bee but I thought osmosis was the diffusion of water?
ELFCloudGamer
I found a link that MIGHT help you understand, but You Tube is user hostile about people putting links in their comments, so I can't put it here.
I couldn't find it on Google. I'm not that Internet literate.
I wish You Tube didn't have a bee in their bonnets about putting web site links in their comments section.
But for the record, the site I visited claimed not to fully understand how all of it happens.
ATP ase Na+/ K+ is usually in charge if that
Thanks.
What playlist is this part of?
The entirety of the action potential (phase 0) is due to the Ca2+ ions. Na+ ions must influx in order for the membrane to reach the threshold, which then leads to the action potential. Just a misunderstanding of wording. :)
Thank you so much .
U R amazing 💐💐
Thaaaaaaanx soo much :) very helpful video
Thank you!!!!!
awesome!!!!
15:36 lol
lmao
okay im not the only one noticing this lol
some of the text book says that the Na channel closes after the rapid depolarization, and the beginning of the re-polarization. What's your opinion on it?