Cardiac Action Potential (Pacemaker AP: part 2/6)

[jonabank]

0:39 I prefer the "funny channels"

[idiotkrati]

But there is no resting potential on SA nodes, is it? It fires spontaneously at -40mV.

[nourane21]

the funny current allow both,sodium and potassium INFLUX and not the opposite

[boredious]

@nourane21 yeah, i was told the same thing

[rottingapplez]

your videos help me a lot! thank you.

[aashayein]

WOW! this is brilliant - i'm trying to learn all of this for qualification exams but I don't have classes/lecturers to teach it to me.... your explanation is fantastic and saved me hours of time!

[darrylportelli]

thank you... very very helpful. youtube is a good source of explenation!!! 

[TheLourdesherrera]

I totally wanna borrow his notes

[Hameedalamkhan]

as patassium channels open so potassium leavs da cells carryng da postv charge so the charge inside da cell again becoms negative....got it

[jolanwix]

4 people don't have Na+ Fun channels

[Guitarristandgoats]

Really, i understood it at the first view, ur da boss! :P

[rougethistle]

Thank you! YOU ROCK!

[bashirtalha93]

ur a magicciian bro........Bless U

[simplyjayce]

the teaching is great! just to clarify, shouldn't (B) [L-type Ca channels] in the chart be on the -30mV instead of 0mV? i thought that's where it opens?

[SuperHunaid]

thanks a lot man, these videos are excellent.

[n2kapur]

Agreed!!! you are an amazing teacher!! please continue doing this!

[shannong86]

an excellent vid! thanks!

[DeMuslim]

I just want to make sure from the last part, when the membrane potential reaches 0 mV voltage-gated potassium channels open, does potassium enter or leave the cell? i can't understand what you're saying influx or efflux? if it's entering the cell carrying positive charge how is the cell going back to -60 mV?

Kindly clarify, great video .. thanks ;)

[dalemcmahon]

You have Na+ ions shooting in.....You have Ca2+ ions shooting in.....You have K+ shooting out...

What restores all of these in such a short time so that the cycle can repeat?

Your description is good, but misses out this important point :(

[3cl1ps3]

Just wanted to say thanks for this excellent description, i've been burying my head in textbooks for a while trying to break this down logically and you've cracked it for me in 5 minutes. Thanks again!

[TL3062]

Where is your Ca plateau?

Thanks!

Troy

[jaggysnake3]

@TL3062 This video is talking about the pacemaker cells, not the myocites that actually cause the muscle contraction. It is those cells which see the plateau, described in the next part I think :)

[GhadaDooda]

Really great job!! this is the first time I really get what they were teaching me for the last few weeks =)

[halcyonidealsmusic]

awesome thanks.

[Serpico261]

i have a question...doesnt the pacemaker cell (SA node) reach an overshoot potential up to 30 mV?

[martigra507]

I have a final tomorrow and after 2 months of this stuff in lecture, I understand it and feel ready for the final after an hour and a half of your direction. Thank you so much! How gifted you are to be able to present the concepts so well and to have such a good understanding yourself. Kudos!

[sarah69090]

excellent explanation!!!

[alalalana]

This is beautiful.

[ALI1981USA]

you are much better than the shit stain I am having in Wayne State

[phoenixgold5000]

Brilliant Teacher !!!!!!!!!!

[nakeya52]

You are AWESOME.

[exracon]

w00t good video

[forgotmypassword100]

this guy is amazing :)

[datapks]

thanks

[Serpico261]

so this would mean that the SA period is about 13 ms long..i am right?

[dsouzaliza]

Thanks

[drizzlle14]

your explaination is way better than my book. Thanks a lot!!

[shinitsky]

thank you so much!!! helped me a lot!

[A01126240]

For more information about this topyc check out this article:

Title: What keeps us ticking: a funny current, a Ca clock, or bothe?

Magazine: Journal of Molecular and Cellular Cardiology

Authors: Edward G. Lakatta and Dario DiFrancesco

[A01126240]

good video, however it is not completely correct. The idea of the I funny current as the MAIN PACEMAKER is not accepted, even though it us clear that this current actually participates as a kind of regulator. Most of the investigators now accept the fact that PACEMAKER activity is controled by spontanous rythmic Ca release from the SR, which activates a net Na current carried out by the Na/Ca exchanger and responsible for depolarization and further opening of R and L-type Ca channels.

[cassdarlin21]

I thought the funny channels were leaky channels, and were always open?

[Cybergriffey30]

Part 1: In a resting cell membrane, there are higher concentrations of Na+ outside the cell and K+ inside the cell. This creates a gradient that both will flow down i.e. Na+ will accumulate inside the cell and K+ will accumulate outside the cell. Na/K ATPase will help remove this accumulation by moving 3Na+ out of the cell and 2K+ inside the cell. Because more Na+ is leaving, this creates a net positive charge outside the cell. Therefore, the resting membrane potential is around -70mV.

[lbreakzl]

When does the potassium accumulates in the cell? It seems like its always passing out of the cell. Is it accumulating with the help of endocytosis?

[hyperhighs]

@lbreakzl I would assume the Na/K-ATP pump restores it.

[lbreakzl]

@lbreakzl so the Na/K-ATP pump is restoring potassium during the depolarization after those funny channels closes? Sorry to bother you =) its been a while since youve uploaded this video... Im just freaking out because of that physiology exam...

[spyked1]

@lbreakzl Na+/K+ ATPase actively removes Na+ and adds K+ all day long. And nights.

[okmgarh]

very nice but, phases were not marked!!?/

[jinsjohny1]

Cheers dude! Explained it way better than my lecturers. Keep up the good work! :)

[kash959]

little point. at 3:23 you talk about hyperpolarization. I think you are referring to the threshold value of -45.

hyper = more active, extreme, beyond

hyperpolarization is when the potential difference is even lower than -60 say something like -80. in fact one of the ways to inhibit nervous activity is through hyperpolarization as it makes it harder to reach the threshold. thanx :)

[rryderz]

This is great great review. If only an instructional video existed for all the major concepts in medicine...

[twmd]

Good explanation. But the axis is wrong.

T type channels take the membrane potential(MP) up to about zero then the opening of L type channels drive it to around +40mv.

[myexocrine]

@twmd

I have action potentials in autorythmic cells at -60, -40 and then 0 to +1mv. I have seen resting membrane potentials at -90, all or nothing at -60 to -55mv then to +30 to +40

[pakibballplaya]

awesome

[fedsome]

Awesome... keep posting them

[carinadaifu]

wow .. no words .. i mean you made it so simple jus buy sayn thngs the way they r.... :P

+

[achiles183]

HCN channels are non-gated channels ...i think they are controlled by levels of cyclic AMP, and also cyclic GMP. Sympathetic stimulation causes the levels of cyclic AMP to reach a certain threshold which opens more HCN channels. Is that correct?

[magzrreyes]

You should definitely be a teacher if you're not already one! Great job presenting the info. Easy to follow... learning more from you than in class!

[rosze7]

i lou u for posting this thnx....:D

[monaliza306]

u explains dam good

this is how teachers suppose to do for students

real explanation

the way is best to teach somebody

[patty8860]

You are incredible! How easy to follow and understand. THANK YOU!

[kriziar5]

i can't believe how simple u made that....

[rathaunike]

@y0shibot - check page 508 of boron second edition - the funny currents are called pacemaker channels and the table shows they are HCN and have a Na/K current

[dharmeshdharmesh]

i m fan of urs...mind blowing job

[y0shibot]

hello hyperhighs,

i really appreciate your videos.

they are really helpful.

I'm on my 1st year in medical school.

your videos helped me a lot and it clarified things which were not clear to me.

i would like you know what your sources of your lectures, if you don't mind?

I also would like to ask if, there is really influx of Na+ ions during the generation of impulse of the SA node? according to Berne and Levy, 5th edition and also Boron and Boulpeap, the SA node does not contain Na+ channels..

[ipyonoti]

beautiful explanation

[jummykorn]

Really good Tutorial, You would make a fantastic tutor

[nishanthikka]

That was a great explanation :)

[ELlSSA]

Well explained, much better than my lecturer!

[captfalconXX]

Thanks a million for your efforts.

[virtualetude]

really helpful video!

[alhammadi666]

it's not working -_- !

I really need to review this :\

[Ouci]

EN ESPAÑOL POR FAVOR =)!!

[bronibashinsky]

great explanations! really helpful, you should make more physiology videos!

[lotiebird]

i have a problem with my cadiac...incomplete right bundle branch block..

[magalytaz]

could you please add this video again, it is not opening.

[hyperhighs]

It works .. maybe temporary server problem.. try again another day.

[moenethretro]

weeeeeew, thank youuuu.

i need this for my rotation block :D

[jonahansen]

So the slope of the initial depolarization due to the HCN channels is controlled by an accumulation of Na+ ions? Or?

[Lanthanideatoms]

The slope is controled by ACh, NE, etc.. which decrease or increase sodium flux through the channel, respectively. In the case of NE, it will cause more sodium influx and thus a larger slope. In the case of ACh, less sodium flux and thus smaller slope. Hope that helps.

[jonahansen]

I am asking what is the mechanism between an increased permeability to Na+ and an increased slope. Nernst equilibrium is reached much faster as is seen in nerve action potentials. There must be some sort of integration going on - an accumulation of Na+, or perhaps a discharging of membrane capacitance, or? Without some sort of integration, the potential would immediately plateau at the aggregate of the Nernst potential for all ion permeabilities.

[jonahansen]

After further inquiry, instead of "aggregate Nernst", I should have said "Goldman Hodgkin Katz" equation....

[angad04chahal]

do have videos on neuromuscular junctions??...gr8 vid btw

n how about cranial cavity n deep dissection of neck?

[mem0ries0fy0u]

ahh just wanted i need to see! amazing :] thanks!

[sweet1ne]

That is just so AwesomE! :) Thank you for posting this hyperhigh...I watched this in conjunction with o2demands heartrate video & they work really well together. This is so helpful. I'm glad u posted these up! :D

[nurse01241984]

just wanna clarify something... isn't potassium an anion, having a negative charge... potassium's return into the cell repolarizes the cell, ryt?

[hyperhighs]

NO! cation.

[KingBroilly]

LOL

if you dont know just google it gonna take you 2-4 seconds....

oh my god

[numerid4]

Your videos are very very good.  I enjoy them.

[hyperhighs]

Okay.. never mind, just study in a way that you understand. I'm sorry if what i said confused you. I talk about heart's electrical propagations in part 1/6 of this series.

[kali4niyadood]

thanks hyperhighs!

[ychengwei]

Hey, do you happen to know what is the typical duration of one SA pace-maker action potential? A value on the time-base please? Say, for normal, resting rate. I'm guessing 800ms?

[hyperhighs]

If i remember correctly, cardiac action potential durations are between 200-300msec... but the heart has many different action potentials: atrial, SA node, AV node, Purkinje, Epicardium, and Endocardium... endocardium has the longest duration. So i think maybe SA will be around 200-250msec.

[ychengwei]

Yup I meant the SA pacemaker potential. But if it's 200-250ms, wouldn't that mean there would be 240 to 300 APs per minute (as pacemaker potentials do not rest and just continue on in a cycle)? If there were that many APs per minute at rest, why is a normal resting heart beat only 70-80? Unless one AP does not equal to one beat (which would be quite strange)? Please help!

[hyperhighs]

The resting heart rate is about 75 beats per minute because there is a tonic parasympathetic input to the SA and AV node, which helps slow the heart rate. To increase heart rate, that input is supressed and a sympathetic input to SA node is initiated. Maximum heart rate of the human heart is about 180-200 beats per minute. That's as much as i can help, sorry.

[DJuggz06]

so hard to keep it in my head, thanks for putting that up.

[frozenchaos9]

holy shit you saved me.

[firefly767]

u saved my ass

[pqnomecaben]

this was very helpful, thank you for sharing it! ;)

[looneytunes55]

This is really good! has helped me soo much!!