Na+/K+/Ca2+/Cl- up/down concetration and membrane potential

[laczlacylaci]

---

Members do not see this ad.

I am trying to create a mental cheat sheet for the concentration gradient and membrane potential.
Facts I know:
The cell's inside is more negative than the cell's extracellular space.

Can I assume these:
K+ going into the cell:
1) [extracellular]<[intracellular] due to Na+/K+ ATPase pumping 2K+ into the cell, making overall intracellular [K+] way more than the [extracellular]?
2) It goes against the gradient (because of 1)), and down the membrane potential. (because of the cell is more negative inside, and K+ is a cation, so that is natural to go into the cell)

Na+ going into the cell:
1) [extracellular]>[intracellular] due to Na+/K+ ATPase pumping 3Na+ out the cell, making overall extracellular [Na+] way more than the [intracellular]?
2) It goes down the gradient (because of 1)), and down the membrane potential. (because of the cell is more negative inside, and Na+ is a cation, so that is natural to go into the cell)

I thought of Ca2+ and Cl- as well:

Ca2+ going into the cell:
1) [extracellular]>[intracellular]
2) down the [gradient], and down the membrane potential

Cl- going into the cell:
1) [extracellular]>[intracellular]
2) down the [gradient], and against the membrane potential.

 

[betterfuture]

I would just know that the intracellular matrix is relatively negative, due to other proteins and ions that set up a ~70V potential. The extracellular matrix is more positive. Don't go in memorizing these details because they will be given to you on test day.

I learned a mneumonic/trick that will help you remember what happens after an action potential occurs and the cell tries to restore the electrochemical gradient.

3 Na+ goes out ------ Na+ has 3 characters (the N, the a, and the + sign) thus it goes back out (out has 3 characters as well)
2 K+ go in -------- K+ has 2 characters (the K, and the + sign) thus it goes back in (in has 2 characters as well)

 

[theonlytycrane]

@laczlacylaci I think you have a good understanding of the concept. If you draw out a neuron and Na+ / K+ ATPase in the soma, we'll see that 3Na+ get pumped out and 2K+ are brought in, resulting in a membrane potential that is negative inside relative to outside.

Like you said, there's more Na+ outside and more K+ inside. On an action-potential graph, depolarization is the Na+ coming in and repolarization is the K+ going out.

At the nerve terminal, Ca2+ comes in, triggering exocytosis of neurotransmitters.

 

[laczlacylaci]

@betterfuture That's a sweet mnemonic! I always tried to come up with one, and could never figure out how! Thank you!

@theonlytycrane Thank you as always!