Action Potentials and Contraction in Cardiac Muscle Cells
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- čas přidán 30. 07. 2024
- www.interactive-biology.com - Making Biology Fun
In this episode, I show how the Action potential is generated in cardiac muscle cells and how this results in Contraction of the Heart. When the action potential happens, calcium ions are released from the Sarcoplasmic reticulum, causing the plateau. Calcium ions then trigger muscle contraction.
00:00 Intro
00:20 Review: SA and AV Node and Purkinje Fibers
01:00 How heart muscle cells are electrically connected.
02:08 Conduction velocities
03:14 Why does conduction velocity change from the SA Node down to the Purkinje fibers?
03:51 What happens inside the cardiac muscle cells?
04:13 Action potential chart - Depolarization of membrane potential
04:44 Plateau phase (calcium ions are released)
05:24 Repolarization of cardiac muscle cells
06:16 Release of calcium ions and Muscle contraction
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You missed Phase 0- Phase 1 transition where fast Na+ channel closing, creates initial drop in Em. Phase 2 is the Plateau from the L-type Ca+ channels being open as a result of Depolarization, same time IKr channels are open that pump K+ out of cell. That is the reason for plateau because K+ out off-sets Ca+ going into the cell. Influx of Ca+ causes Sarcoplasmic Reticulum Ca+ release, this reults in cross-bridge cycling & muscle contraction. The Plateau is the ST segment of ECG. Overall this explanation requires a few more additions to be correct.
@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!
@lovelylatina207 Thank you! Stay tuned for more Biology videos coming very soon!
Wow! Your passion makes me learn this stuff even more! You have a gift, thanks for making this so manageable!
I was failing one of my biology classes until I found your channel. You are amazing at explaining everything.
Thank you so much. I had difficulty before watching this episode. This episode has made it so easy for me to understand about action potential and phases of cardiac muscle contractions. Once again thank you very much. God bless you.
Thank you so much !!!! i'm an occupational therapy student in uni and this was amazing helped me a lot.
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!!!!!!
You're videos so unbelievably helpful. Thank you so much for being such a genius but still being able to relay the information!
Your voice is deep, velvety, and silky smooth my man, Definitely making biology fun.
100% True
HI, there. Thank you for this video.
What is the difference between the red and blue curves. I did not get that very well. Makes sense to highlight their difference?
Is it the membrane potential vs. the tension in the cardiac muscle cells?
This saved me hours of reading and stressing over this topic... Very helpful esp. since I have a test tomorrow.
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.
wow this video helped me so much, it made is so much simplier to understand! Thank you so much!
WOW...I Love you. Got a test tomorrow and this was the thing i was struggling with for a while.
Excellent video. A great refresher for me. Thank you!
Will appreciate it if the Bundle of His was also mentioned...Thanks! =) The videos are REALLY helpful. Good job!
@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.
Used this to study for my MCAT. Very good videos. Will be looking for Kidneys next lol
I love you lesley. You make physiology really easy for me
No comment..... just Brilliant!!
thank you. these videos are amazing and have been so helpful
@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.
thank you, that was great demo
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?
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.
Thank you Sir!! this helped me a lot!!!
what is action potential duration ? What is the difference between APD and ERP?
Is calcium also release by the terminal cisternae in Cardiac muscle?
these viedos are fantastic for review :)
this video rocks! thank you!!
thank dude because of u all concept r clear
Thanks for the video! Very helpful. But isn't the part you've labeled Purkenje the left bundle branch of His?
THANK YOUU SO MUCH FOR THIS! i UNDERSTAND THIS NOW!!
Very great videos! Greats Appreciated.
this is most excellent
Thank u so much for these videos
Great! i hav an exam after tomoroow i needed this thanx
Video uploaded 11years ago 😱 .... NICE VIDEO SIR 🙏
Thanks. I guess the way the heart functions hasn't changed in 11 years 😀
Does The action potential includes Depolarisation phase and the plateau?
Thank you so much! I thought this was going to cover PQRST....
I cover that in this video - czcams.com/video/TISR6RS6gEI/video.html
@cid6000 You're very much welcome!
why does K+ ion release cause muscles to relax? Really helpful video!! God bless you.
M Ali Under physiological conditions, K+ ions will move OUT of their channels (efflux), which is the opposite for Na+ and Ca+.
Therefore, the loss of charge from the cell from K+ efflux will bring the membrane potential down (make it less positive) which will terminate action potential spikes (once sufficiently below threshold) and in turn terminate muscle contractions.
Perfect !!!!!
@CecilieWhipps We love saving lives. Especially with Biology ;)
you are my hero doctor
Thank you a ton!!
hi,thanks for this amazing video .however i wanna tell u that the calcium ions enter the membrane of the fiber in the heart .Not released from the endoplasmic reticulum as u mentioned .this is true in skeletal muscles but not here in a myofiber of the heart
Actually both happen. It's called Calcium induced-Calcium release. It's unique to the cardiac cells.
what is the "extra event" that occurs in cardiac muscle?
you didnt mention movement of inons in different phases...
Where is the bundle of his located ? Has it the same role ?
Thank you from the SA node of the heat of tired med student ♥️
This was my favorite comment for the month 😂😂😂
Thank you
It's 3am,exam at 10:30am. All I can say is Thank You!!!
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).
thank you very much
If calcium is also released in skeletal muscle cells, why is there no extended refractory phase there...
This is a fantastic question, and I think using graphs would be the best way to explain. But since I have no visual aid, I hope to point you in the right direction:
So - I think thing we're confusing here is skeletal MUSCLE depolarization and the NERVE depolarization. The muscular depolarization of skeletal muscle lasts a long time compared to the instantaneous depolarization/re-polarization cycle (action potential) of a muscle's associated nerve.
@NeedsAHardOne Thank you! :)
Thanks a lot mate
@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+)
Moreso* Also they extend directly from the AV node
Why does Ca cause the release of aceytylcholine and cause muscle contraction, yet excess calcium results in muscle weakness? Can you tie that in with the action of Ca channel blockers and their negative dropotropic and inotropic effects? Thank you, and I love your videos.
I do understand the Ca channel blockers decrease vascular resistance, causing dilation and thus the afterload is reduced, so that results in a negative inotropic and dromotropic effect. I guess I am confused about the seeming paradox of hypercalcemia causing muscle relaxation/weakness and yet calcium as a cause of muscle contraction and vascular resistance.
Hello! I am from Greece and I am studying Biology in Germany. Your videos are really very very helpful!!! I have a stupid question though: does the plateau phase exist only at the cardiac muscle cells or generally at every muscle of the body? I mean, it sounds logic because there is a Calcium release at every muscle...
Plateau only in cardiac muscle. It prolongs the action potential to as long as 300 msec. This prolongation plays a role in triggering muscle contraction. Recall that in skeletal muscle if the frequency of action potentials is high enough the muscle will enter a state of tetany in which the muscle remains continually contracted. If this happened in the heart, blood flow would stop, since refilling of the chambers requires that the heart relax.
Also, contraction of cardiac muscle requires the contribution of extracellular Ca2+. All during the plateau phase Ca2+ is entering the cell from the extracellular fluid, contributing to total intracellular calcium concentration.
I agree with steve schneider
Are you a Trini??
Good stuff!
Yes. AP ends once it reaches the resting potential again.
Thank U
Awesome
what was the difference between the red and the blue curve. I got that the blue curve represent the cardiac contractile muscle AP but what was the red curve for. it confused me a little
blue is the contractile response so how the muscle reacts to the action potential
Link of episode 42 ....please send
Sorry for the delayed response. Here you go -
pulse.ly/bawg7xglcm
@kerryvp St. Maarten :)
Also if the heart did have tetanic contraction it would fatigue, which we do not want as our heart is needed all the time.
gives time for ventricular filling and prevents tetanic contraction
👏👏
Wronggggggggggg!!!
Thank you