Membrane potentials - part 2 | Circulatory system physiology | NCLEX-RN | Khan Academy
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- Опубликовано: 5 окт 2012
- Find out how a cell that is permeable to one ion can become charged (either positive or negative) if there is permeability and a concentration gradient. Rishi is a pediatric infectious disease physician and works at Khan Academy. Created by Rishi Desai.
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K+ needs to make up its mind and decide where it wants to be
😹😹😹
Great video. I am however skeptical of Dr. Rishi's credentials of actually being a Dr. His handwriting is way too good for him to have a M.D.....
You really helped in making med school a bit easier! Thanks so much!
Good drawings--not too cluttered, easy to read and follow. Also the material was broken up well (parts 1 and 2). Very helpful and well-made presentation, thank you very much!
What software are you using to draw on screen for this presentation? Thank you.
Fantastic! Thanks a lot!!
This was really helpful. Cheers.
You are a genuis! thanks!! made my day!
helping me very much at college! thanks man
This video is really great
The most underrated video in youtube talking about this topic
Funny how people jump at any opportunity to be appear smarter than what they really are. Yes, we all know the unit for potentials is voltage and that the "M" in Vm stands for "membrane." He clearly had a blonde moment (yes, I know he's not blonde) and caused no harm in the process, because there was no misinformation. You're becoming a doctor via RUclips. If you can't tolerate moments like this, then I suggest you read a textbook instead.
georgyorgy2 PREACH IT, even lecturers have goofs. It’s not a big deal
i don't see the harm in pointing it out.
:) I learn many things and the lectures are very clear, excellent. But I was surprised to see that lecturer said that he doesn't know where V comes from. This is of course because of concepst shared in different disciplines and normal. V comes from voltage, equation comes from Nerns Equation. I am studying electrochemistry and my discipline is chemical engineering he is a doctor, this is normal. Besides this as a medical doctor he teaches better than most of the chemists :)
You sound like Dr. Jackson from Gray's Anatomy! And your video is very helpful :)
Helpful thanks
First of all thanks for that explanation
And I want to ask you ,if you can explain to me why don't we have an membrane potential of there is a concentration gradient but there is no permeability ??? Because at that point we will have more potassium (inside or outside whatever ) and according to that it must create a membrane potential !??!!!
Doesn't the V come from voltage since it expresses the voltage of the membrane (or "membrane potential")
Exactly this.
Voltage= Potential difference
Exactly. Kinda disappointing he didn't know that.
@@sasom7274 relax. he’s a human. he has shortcomings. don’t be lame about it.
@@urmotha48 I wouldn’t be comfortable lecturing to millions if I wouldn’t be certain I am capable.
but also I think we should note that the permeability of sodium at resting membrane potential is very low so we would have to assume that its impermeable to it , most of sodium channels are closed , so sodium has no effect on the membrane potential...but potassium channels are more opened , which gives assumption to that its the only cation permeable hence its major contribution to the creation of the membrane potential
when you add the positive charge, then you get to -42 and then climbs back up to -92mv again when the K+ leaves the cell. But if you keep repeating this, the equilibrium potential eventually decrease
thanks
love it
This video saved me from going insane. Thanks.
He said millivolts around 2:15. He knows that V stands for voltage. I just think he isn't sure like how to derive the V or something.
to all of you who wonder how electroneutrality is maintained even though there is sodium involved and should contribute to the change. It's very simple, equation in the video is only correct if we assume that there is only one type of ion, so if we would take for example sodium to consideration we would need to use different equation which is called goldman hodgin katz equation. So equation in the video (which is btw called nernst equation) gives us a clue what would happen if there was an excess of K+ ions inside the membrane compared to other ions so the membrane potential would shift towards the -92mV...thats the biological significance of nernst equation. So to put it together, if you want to calculate actual membrane potential of thr cell - use katz equation and if you want to calculate membrane potential if only one ion was present - use nernst equation (the one in the video).
correction: electroneutrality is maintained even though there is sodium involved and should contribute to the change. Equation in the video is only correct if we assume that the membrane is only permeable to one type of ion, so if we would take for example sodium channels to consideration we would have to use different equation which is called goldman hodgin katz equation. So equation in the video (which is btw called nernst equation) gives us a clue what would happen if the membrane would be much more permeable to K+ compared to other ions. A good example for that are glial cells. So to put it together, if you want to calculate actual membrane potential of the cell - use katz equation and if you want to calculate membrane potential if the cell is only permeable to one ion - use nernst equation (the one in the video). Hope this makes more sense
Jakub Szudrwaski
First of all thanks for that explanation
And I want to ask you ,if you can explain to me why don't we have an membrane potential of there is a concentration gradient but there is no permeability ??? Because at that point we will have more potassium (inside or outside whatever ) and according to that it must create a membrane potential !??!!!
How u can do these drawing?
If this is how to calculate membrane potentials, then what is the goldman equation for? cuz they give different answers.
6:26 doesn't the V comes from Voltage ? Seems to me that membrane potential is actually a voltage (potential difference) btwn the inside and the outside of the cell.
Vm = memb. Potential or simply membrane Voltage sir !
Where did you get the concentrations? Are they different from Guyton's concentrations?
i got confused reading guyton, so here i am watching this
potential difference is also called as voltage which has a sign of "V".
yes that's what i thoguht
How is electroneutrality maintained in the cell? If the diffusion of K+ out leaves a equilibrium potential within the cell which is slightly offset by the Na+ equilibrium potential thereby generating a membrane potential, wouldn't the charge inside the cell be different than the charge outside the cell? Or, is it just that the charge difference is a result of the location of accumulation of charge, ie. near the surface of the membrane. Any help would be appreciated!
Thanks!
in chapter 2, pg 32, in the 5th ed of Purves' Neuroscience, it states that while the flow of ions is enough to change membrane potential, the amounts are so small that the overall concentrations in both extracell & intracell compartments remain the same, thus maintaining electroneutrality. and to add to that, you have more than one species of ions interacting, that are equal and opposite (k+ & cl- for example.). so really the charge inside the cell that is enough to change Vm is just in the membranes proximity.
Equilibrium potential = Reversal potential?
but surely if the K+ ions enter back when the charge increases back to -92mV, the charge will then decrease again because the anions are now being cancelled out by the new K+ ions and not contributing to the overall negative charge?
1:11 I thought potential measures energy per unit charge difference not the amount of charge difference
funky stuff hunh ?
Vm comes from membrane's Voltage (potential)
V comes from Volts, but E might be more appropriate.
No V comes from' Voltage 'actually
Actually it's mV (milivolt) - electromotive force
Even if you change the permeability to one ion, wouldn't the equilibrium potential stay the same? (ref to about 3:55). Changing the permeability (I think) would only change the rate of attaining equilibrium potential, not the eventual value.
yeah if you're injecting positive ions it seems like the potential would change because you can't create more negative proteins instantly
V is voltage
4:25 Is he Satan's Physician?
If you're injecting positive ions...but they aren't permeable...then they will permanently be trapped inside the cell. And if they are inside the cell they will neutralize some of the negative protein anions. Thus the potential membrane potential will be less...because the -92 is due largely to the number of anions. But if these positive ions are neutralizing some of these protein anions, they won't be able to drive the potential back down....unless the cell instantly creates more proteins with negative charge.
Here it feels like charge and voltage are treated as the same thing.... I thought they were 2 completely different concepts. Can someone explain?
+Michael Chait They are not the same thing but nor are they completely different concepts as a difference in charge is here the basis for the voltage (potential difference). Charge is dictated by the relative numbers of protons and electrons in an ion: a neutral atom of potassium 'K' readily loses an electron to form a cation, the more stable positive K+ ion; or a neutral atom of chlorine gains an electron to form a anion, the more stable negative Cl- ion. When you have more cations than anions in one place you talk about a region of positive charge. Conversely, if you have more anions than cations you have a negative charge. If you watch the video again you will see that the cell membrane is permeable to K+ ions and due to the concentration gradient they move out of the cell with their positive charge. The voltage is created because with the net movement of these positive ions the membrane inside the cell is left slightly negative having lost them, and on the outside it is slightly positive having gained them. This difference in charge across the membrane is what is shown by the voltage of -92mV. Hope that helps.
@8:20 it looks like a smiling stick figure (the one with two positive charges)
Why the hell would anyone dislike his videos?
I guess the V comes from 'voltage'?
sorry about that
what the number 61.5 represents for ?
& the log .. do me a favour & remind me of it
I'm not good at maths
61,5 = (R * T) / (z * F).
R = gas constant (8,31 J/mol*K)
T = temperature (310 K = 37 C = body temperature)
z = valence of the ion (+1 for potassium)
F = faraday constant (96500 C/mol)
I like all of khan Academy video's and they have been helpful. But how can you as a physician not know V stands for voltage? Its basic undergraduate level knowledge. It makes me question whether I should keep watching these videos.
I support u there hey, like really
It actually stands for vagina. Do some research.
6:25 I'm not sure if this is a joke or you're being serious but I really hope you know the "V" stands for "voltage"...
+João Soares dont be like that mate, it happens to everyone
+Khandir Ghaleicus If you're in your first year of medical school, sure; if you're an MD working for Khan Academy it definitely shouldn't...
+João Soares it doesn't matter if he doesn't know what the V stands for, he really doesn't have to. The important part is that he knows how it works. Nitpick much?
+João Soares He definitely knows that "V" stands for "voltage". He clearly says "millivolts" when he talks about the membrane potential's unit.
+João Soares congrats on keeping the douchebag medical student stereotype well and alive. Dick.
no seriously someone walk me through where the 61.5 comes from i dont even understand how it works even with the values (i have someone confusion of what z is too, i know its valency but what is the value to put into the calculation?)
Yes patronise me if you have to i dont care i want to learn this
+Rubin Joseph assuming 61.5 is just all the constants, whatever they may be, plussed multiplied together so you dont have to drag all those constants with in an equation
+Dehan Ferreira so 61.5 is suppose figure???
+ammar yasir Okay I'll walk you through the formula used. They use the Nernst equation. There are three constants in that equation R, T and F. So you know they will never change. So they are allready substituted it in the equation from the begging (This is the 61.5 in the video). This makes it easy seeing that you do not have the redo all three substitutions, you'd rather just remember the value they make. You can go test it. Google the nernst equation, take (RT)/(F) and just substitute all of the constants in and then see the value you get. It should be about 61.5.
The Z is the valency. It can be read of the periodic table. As you are supposed to know all group 1 elements have an valency of +1 and group 2 has an valency of +2. So for the Ca the 61.5 will be divided by 2 and thats how they get the 30.75.
Nernst equation (Vk)= (RT)/(zF).ln[k out]/[K in]
Thumbs up if this correct!
life saver,,,thumbs up
The V comes from Voltage (the electric potiential difference between two points)