Electrochemical Gradient

In this video Paul Andersen explains how the electrochemical gradient is a combination of the chemical and electrical gradient of ions. As ions move across a membrane the potential change creates a hidden force that isn't always apparent.
PhET Simulation with membrane channels - phet.colorado....
ASU Nernst Goldman Simulator - www.nernstgoldm...
Music Attribution
Intro
Title: I4dsong_loop_main.wav
Artist: CosmicD
Link to sound: www.freesound.o...
Creative Commons Atribution License
Outro
Title: String Theory
Artist: Herman Jolly
sunsetvalley.ba...
All of the images are licensed under creative commons and public domain licensing:
Basis_of_Membrane_Potential.png (2673×1876). (n.d.). Retrieved December 20, 2016, from upload.wikimed...
File:Potassium-chloride-3D-ionic.png - Wikimedia Commons. (n.d.). Retrieved December 20, 2016, from commons.wikime...
GIBERT, J. P. (2016). Français : SalièreEnglish: Salt shakerDeutsch: SalzstreuerEspañol: SaleroItaliano: SalierePortuguês: SaleiroΕλληνικά: Αλατιέρα. Retrieved from commons.wikime...
Häggström, B. W. using this image in external sources it can be cited as:Blausen com staff “Blausen gallery 2014” W. J. of M. D. 15347/wjm/2014 010 I. 20018762 D. by M. (2014). English: The sodium-potassium pump and related diffusion of sodium and potassium between the extracellular and intracellular space. Retrieved from commons.wikime...
Navarre, Z. I. of. (2016). English: A 3D rendering of an animal cell cut in half. Retrieved from commons.wikime...
Somepics. (2015). English: Light-dependent reactions of photosynthesis in the thylakoid membrane of plant cells. I redrew and formatted it for a better quality SVG file. Retrieved from commons.wikime...
The Nernst/Goldman Equation Simulator. (n.d.). Retrieved December 20, 2016, from www.nernstgoldm...
Villarreal, L. M. R. (2007). English: Example of primary active transport, where energy from hydrolysis of ATP is directly coupled to the movement of a specific substance across a membrane independent of any other species. Retrieved from commons.wikime...
Basis_of_Membrane_Potential.png (2673×1876). (n.d.). Retrieved December 20, 2016, from upload.wikimed...
File:Potassium-chloride-3D-ionic.png - Wikimedia Commons. (n.d.). Retrieved December 20, 2016, from commons.wikime...
GIBERT, J. P. (2016). Français : SalièreEnglish: Salt shakerDeutsch: SalzstreuerEspañol: SaleroItaliano: SalierePortuguês: SaleiroΕλληνικά: Αλατιέρα. Retrieved from commons.wikime...
Häggström, B. W. using this image in external sources it can be cited as:Blausen com staff “Blausen gallery 2014” W. J. of M. D. 15347/wjm/2014 010 I. 20018762 D. by M. (2014). English: The sodium-potassium pump and related diffusion of sodium and potassium between the extracellular and intracellular space. Retrieved from commons.wikime...
Navarre, Z. I. of. (2016). English: A 3D rendering of an animal cell cut in half. Retrieved from commons.wikime...
Somepics. (2015). English: Light-dependent reactions of photosynthesis in the thylakoid membrane of plant cells. I redrew and formatted it for a better quality SVG file. Retrieved from commons.wikime...
The Nernst/Goldman Equation Simulator. (n.d.). Retrieved December 20, 2016, from www.nernstgoldm...
Villarreal, L. M. R. (2007). English: Example of primary active transport, where energy from hydrolysis of ATP is directly coupled to the movement of a specific substance across a membrane independent of any other species. Retrieved from commons.wikime...

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this video really helped me! the demonstration was simple and the commentary was very straightforward which really helps :)

[@isaacdouglas1119]

Thanks for making this helpful video! I wanted to clarify my understanding of the underlying physics so I would appreciate if you could correct any misconceptions I have.
Statements such as "the chemical gradient pushes ions from regions of high concentration to low concentration" and "the electrical gradient pushes positive ions from regions of high positive charge to low positive charge" (paraphrasing) seem slightly imprecise (but I understand the didactic necessity for abstractions). It's not that there is a physical law that the chemical gradient pushes ions from regions of high concentration to low concentration but rather that, due to Brownian motion, it is more likely ON AVERAGE for particles to move in the direction of low particle concentration regions. Thus, the "force" exerted by the chemical gradient is just an emergent property of Brownian motion. It could happen by chance that a group of particles in one region move into a smaller region and become even more concentrated. But, over time, this situation is less likely to occur than diffusion.
I would similarly press the abstraction of the electrical gradient exerting a "force" as well. Since the electromagnetic force extends infinitely (and decreases proportionally to 1/r^2), every charged particle exerts an electromagnetic force on every other charged particle (and this abstraction can be broken down further to the subatomic level but I don't think that's necessary for this topic). Thus, there is not an electrical gradient that pushes the K+ ions towards the other side of the membrane. Rather, as the concentration of K+ decreases in the bottom side (and the ratio of Cl- to K+ increases), there is, ON AVERAGE, a stronger electromagnetic force exerted on the top-side K+ ions toward the bottom side. But, this is not necessarily always the case. Let's imagine this situation: momentarily, due to Brownian motion, the remaining K+ ions in the bottom side moved right against the membrane (top of the bottom side) while the Cl- ions (all on the bottom side) moved to the bottom of the bottom side. At that moment, for any of the K+ ions in the top side, the y-component of the vector representing the summation of the forces of all the other molecules on that K+ ion would point away from the bottom side. When we say the electrical gradient "pushes" the K+ ions toward the bottom side it is rather that, on average (over time), the moment-to-moment average (over all the other ions) force exerted on each top side K+ ion points toward the bottom side (not directly toward it per se but I mean the summated forces vector's angle (where pointed exactly left = 0 radians and pointed exactly right = π radians) is more likely to be between π and 2π than 0 and π). I.e., much like the chemical gradient, the "force" exerted by the electrical gradient is an emergent property of many individual electromagnetic interactions.
I just had the thought that perhaps the membrane has an effect on the electrical gradient somehow (negligibly?). Anyway, thank you for reading and I would love to hear any corrections to my understand of the underlying physics.

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Why can TH-cam videos from 5+ years ago always explain concepts so much better than my current professor.......

[@nadyaamalia4101]

thank you so much! it is the best explanation I've got so far about electrochemical gradient

[@larrysizemore2891]

Something I think you should note is that when potassium is entering the cell in your example, the inside of the cell is potassium filled, (like is attracted to like), therefore it moves down it's concentration gradient (simple diffusion). If it were to enter a cell filled with hydrogen ions, it would require a channel protein and would move up it's concentration gradient because it's simply not attracted to the hydrogen ions. This is the electrochemical gradient...

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you explained this so well, thank you for making this video

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This was so helpful. So well explained and clear. Thank you

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I’m confused as to why it’s 37/13 are we supposed to know how many on each side exactly or just a general ratio

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[@marihanbadr1271]

Thank you so much, i never quite understood the electrochemical gradient before watching this. However, something is confusing me. What's the difference between the equilibrium potential and the resting potential?

[@nandiganavishal]

characterize membrane needs permittivity, charge regulation with time, ion-ion, particle-membrane interactions only some membrane journals publish them numerical are few I suppose

[@rkpetry]

*_...where does space, fit into your equations-when K⁺ gets across the membrane it's going to spread out (you implicated this already), but how far, does it go, equationally, and what-becomes of the chemical and electrical gradients and potentials near, far, and-farther..._*

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When is an electrostatic gradient the strongest during the change in a neuron membrane potential?

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[@lauraraexoxo5628]

Okay so I have been struggling with the fact that the overall concentration inside and outside the cell stays the same, bc of electrostatic force, yet if more ions leave/ enter the cell to reach their equilibrium potential, doesn't the concentration change at least for a short period of time? Like I get that it is pulled back into or out of the cell bc of electrostatic force, but still? I feel so dumb for not getting an intuition for this sorry

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Excellent explanation

[@rkpetry]

*_...p.s. Why is, the Nernst Equation-it obviously doesn't work at quantum levels where a single atom has a chemical gradient to cross the membrane, but once across it has the same to go back-so it's not-really a 'gradient' but maybe a 'half-gradient',-and why log when log 1 = 0, and log 0 = -∞, for that one lone atom ('wee-haw, giddy-app')..._*

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does water molecules enter cells by electrochemical gradient?

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[@carloss.182]

If the cell membrane were hyperpolarized to a resting potential of -110 mV, what would be the effect on the potential opening of K+ channel?

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assuming the equilibrium potential of K+ is -90mV, the K+channels would open up to release more k+ions outside the cell in order to bring up the resting membrane potential of "-110mV" closer to -90mV.

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