Membrane Potential, Equilibrium Potential and Resting Potential, Animation
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- čas přidán 29. 08. 2024
- (USMLE topics) Understanding basics of ion movement and membrane voltage, equilibrium potential and resting potential.
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Voice by: Ashley Fleming
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Membrane potential, or membrane voltage, refers to the DIFFERENCE of electric charges across a cell membrane. Most cells have a NEGATIVE transmembrane potential. Because membrane potential is defined RELATIVE to the exterior of the cell, the negative sign means the cell has MORE negative charges on the INSIDE.
There are 2 basic rules governing the movement of ions:
- they move from HIGHER to LOWER concentration, just like any other molecules;
- being CHARGE-bearing particles, ions also move AWAY from LIKE charges, and TOWARD OPPOSITE charges.
In the case of the cell membrane, there is a THIRD factor that controls ion movement: the PERMEABILITY of the membrane to different ions. Permeability is achieved by OPENING or CLOSING passageways for specific ions, called ION CHANNELS. Permeability can change when the cell adopts a DIFFERENT physiological state.
Consider this example: 2 solutions of different concentrations of sodium chloride are separated by a membrane. If the membrane is EQUALLY permeable to BOTH sodium and chloride, both ions will diffuse from higher to lower concentration and the 2 solutions will eventually have the same concentration. Note that the electric charges remain the same on both sides and membrane potential is zero.
Now let’s assume that the membrane is permeable ONLY to the positively-charged sodium ions, letting them flow down the concentration gradient, while BLOCKING the negatively-charged chloride ions from crossing to the other side. This would result in one solution becoming INCREASINGLY positive and the other INCREASINGLY negative. Since opposite charges attract and like charges repel, positive sodium ions are now under influence of TWO forces: DIFFUSION force drives them in one direction, while ELECTROSTATIC force drives them in the OPPOSITE direction. The equilibrium is reached when these 2 forces COMPLETELY counteract, at which point the NET movement of sodium is ZERO. Note that there is NOW a DIFFERENCE of electric charge across the membrane; there is ALSO a CONCENTRATION gradient of sodium. The two gradients are driving sodium in OPPOSITE directions with the EXACT SAME force. The voltage established at this point is called the EQUILIBRIUM potential for sodium. It’s the voltage required to MAINTAIN this particular concentration gradient and can be calculated as a function thereof.
A typical RESTING neuron maintains UNequal distributions of different ions across the cell membrane. These gradients are used to calculate their equilibrium potentials. The positive and negative signs represent the DIRECTION of membrane potential. Because sodium gradient is directed INTO the cell, its equilibrium potential must be POSITIVE to drive sodium OUT. Potassium has the REVERSE concentration gradient, hence NEGATIVE equilibrium potential. Chloride has the same INWARD concentration direction as sodium, but because it’s a negative charge, it requires a NEGATIVE environment inside the cell to push it OUT.
The resting membrane potential of a neuron is about -70mV. Notice that ONLY chloride has the equilibrium potential near this value. This means chloride is IN equilibrium in resting neurons, while sodium and potassium are NOT. This is because there is an ACTIVE transport to keep sodium and potassium OUT of equilibrium. This is carried out by the sodium-potassium PUMP which constantly brings potassium IN and pumps sodium OUT of the cell. The resulting resting potential, while costly to maintain, is essential to generation of action potentials when the cell is stimulated.
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thank you so much! this is much clearer than a 150 mins lecture!!!
exactly. been trying to find out what in the world my prof is communicating in that mess of a lecture, and here I go, a four minute video got me up to speed.
i understood the whole lesson just by watching 2 minutes of this video. Thank you so so much!
This is the cream of our hours long reading and lectures
Thankuuu
I just started grad school, I really appreciate this video. I can understand my notes now
exellent, simplified and still accurate explanation!
Good, simple, easy-to-understand videos from Alila in general, with some errors in the details (e.g. starting time point of relative refracter period, or threshold potential for the late Kv channels in the action potential video). While these videos are good (overly simplified) starting points for the referred topics, I would warmly suggest medical students etc, to put effort in understanding/learning their text books and university lectures as well, if they want to remain on the safe side for passing their exams.
I’m still confused
This is very confusing topic ...but now my concept has cleared...after watching 3 or 4 times
Work harder
Great and detailed explanation, good graphics.. Very helpful to understand
Great and simplified explanation!!
Useful video to understand body Biology, better than reading a book !
True thanks about grateful
Active and passive diffusion of electrical and chemical ions through cellular membrane . Perfect information
This video is an artwork.. Thank you
Thank you so much.....this vedio os better than our lecture of two hours👍👍👍
CLEANLY EXPLAINED
That was super informative and soo easy to understand.. Thank you 😁
very best explanation i have ever seen guru, thank you
Great video...need more of these medical topics pls ma'am
great video and nice illustration. thank you.
That is very useful thanks so much 👏🏻👏🏻
soo easy to understand.. Thank you
You are welcome!
Great, thank you. So simple.
thank you love the video. Why does the equilibrium potential need to be positive for Na+ inorder to put sodium out of the cell?
The equilibrium potential needs to be positive because like charges repel. Only then the sodium ions will go back to the outside of the cells.
@@htetmyatmin223 Could you explain why does it have to be negative to potassium?
@@henricostel7273 Since potassium ion is positive charge and the direction of it's gradient is to flow out of the cell, the equilibrium potential has to be negative to attract these potassium ions back inside the cell because unlike charges attract.
@@htetmyatmin223 wonderful explanation. Thank you!
thank you ! that was very helpful .
Very well Explained
Why is cell interior negative charged even though there’s more cations and less anions than outside ?
There are large molecules inside the cells that carry negative charge: proteins, nucleic acids
clear and concise
Perfect, thank you!
This was so helpful thank you so much btw at 0:19 I thought the inside of the membrane being considered more negative was because there were less positive charges instead of it being because of more negative charges
The inside negative charge is due mostly to large negative charges from proteins and nucleic acids.
@@Alilamedicalmedia I had no idea thank you so much!
At 1:52, how to know that at which point the flux of Na+ ions across the membrane will stop?
As soon as Na diffusion potential is able to counteract Na conc.gradient
What cherry said
Thank you so much this was so helpfull :)
can someone please explain to me why the equilibrium potential of K+ is negative? negative and positive attract each other, and you want K+ to enter the cell again, so why isnt it positive?
Bcz when potassium get into the neuron simultaneously sodium will move outside and for every two k+ ions are actively transported inward and three Na+ ions are pumped out so as more positive charges pumped out than going inside the inner environment get more negative than outside!
This is because calculating membrane potential is a comparison of the outside of the cell (ground) compared to the inside. If your voltage is positive, this means that the inside of the cell is more positive compared to the outside. This would force K+ out, which is the opposite of our desired effect. Thus, K+ requires a negative voltage-a more negative inside- to draw that K+ back in.
I finally understand this!!!! Thank you
What does it mean that positive and negative signs represent the direction of membrane potential?
Thanks for emphasizing OOUT!
thank you so much!!
Thanks a lot
Amazing stuff thanks lot
Ma pls make a video on types nerve fibers and neurotrophin
Thanks sir very informative and short video .but plz upload videos in urdu.
Great video thank yuo
At 2.47, how do we calculate the equilibrum potentials?
YOU SAVED MY LİFE
I'm confused
+1
Me too. I don't understand why the potential of the membrane is equal to that of the chloride since the chloride has more negative outside while the membrane has more negative inside.
@@theGuilherme36 hom gout vancom
@@sal941 ???
Guilherme Resende so if romases do nadonades meet anatomical poratesas if you?
Can anyone help me with my EDx course? I couldn't find an answer there:
Cells in the electric eel's electric organ have a larger-than-normal membrane potential, sitting at roughly -150 mV. How might a cell achieve a more negative resting potential? Indicate all that apply.
Higher extracellular K+ concentration
Lower extracellular K+ concentration
(correct)
Higher intracellular K+ concentration
(correct)
Lower intracellular K+ concentration
Why do lower extracellular K and higher intracellular K make the membrane potential greater? Wouldn't more positive charge inside the neuron make the membrane potential smaller?
Why the potential of Na is positive if it is driving inside the cell? ..
So which channel is open?
Thanks
Amazing lec
Thank you.... It's very helpful👍👍👍
THANKS ALOT
It's more than best😍
Thanks for the video. But I was wondering if the channels are different for potassium and sodium. Here You showed only one channel, which I suppose, was for simplicity. Am I right?
I believe they are, dont quote me though
Yeah I'm 99% sure each ion has it's own channel.
The sodium-potassium pump is a special case. Each ion does have its own channel, but the Na-K pump spends ATP to bring K inside and simultaneously push Na outside.
3:18 was what I came for.... thanks
If a neuron has an internal potential of -60mV and an external potential of -20mV, would the potential difference across the membrane be inside minus outside or outside minus inside?
Inside negative, -40 mV as compared to the outside. These are conventions: you compare IC to EC (or subtract EC form IC: -60- -20= -40). As EC is often grounded, it is considered to be not different from Earth potential, that is considered 0 mV (convention again, -70mV - 0 mV=-70 mV= Em, in a typical nerve cell).
I wonder if the equilibrium potential for an ion species is always constant?Lets say,we manually double the amount of Na+ concentration outside the membrane and wait for the Na+ ions to equlibrate,will the ENa still be 6(from your example)?
Short answer: no, it will change. Long answer: www.d.umn.edu/~jfitzake/Lectures/DMED/IonChannelPhysiology/MembranePotentials/EquilibriumPotentials.html
how did she calculate that E was 6??
Great great great👍👌
Let go
We have to admit she has Scarlett johansson's voice 😅 lol .. thank you 🙏
How can sodium move out of the cell when when its extracellular concentration is high?
With a process called Primary Active Transport in which a cell membrane moves Ions against a concentration gradient (or against an electrical gradient). Guyton & Hall: Medical Physiology Chpt. 5
UHAS202212743
So in what way does this pump differ from the voltage gated channel with regards to the action potential?
Mam how do we define the direction of electrostatic force here
Umer Binshabir From positive isotope to negative isotope. The positive will want to move to where the negatives are.
@@sakuraiwaru3299 So it doesn't make sense that chloride move from the negative to the positive.
Because direction of electrostatic force of attraction is from positive to negative
Can anyone tell me why potassium ratio is more than sodium ratio across resting membrane potential?
The drawing is confusing bc sodium potassium pumps pump 3 Na out and 2 K in. The graphic shows the opposite happening.
I don't understand why the inner membrane is negative, because potassium has a positive charge.
Because of the proteins, rna and dna. They have negative charge
Wow
at 2:34 said E of Na is 6, how to calculate this?
6 is the voltage difference. The difference between -3 (on the left) and +3 (on the right) is 6
Thank you @@Alilamedicalmedia if mebrane poteintial Vm=0, what is the concentration of each ion on each side of the membrane? Is Vm=0 meant equilibruum potential too?
@@Alilamedicalmedia -3 - (+3) = -6
@@Alilamedicalmedia And if I have 10 positive and 2 negative ions on the left side and zero ions of any kind on the right side, then how do I calculate when the chemical gradient and electrical forces are going to be at equilibrium?
1:28 no movement because the two concentrations are equal. Ratio is the same=1.0
1000th like+new sub
We have this in 11th grade :((
hey am in 11 th grade too...and my teacher is like sso scary so its hard to understand in class....am depressed
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Lol potassium can't make up it's damn mind!
🥹🙏
아하!
the