- force of attraction of ions to the opposite charge (of the membrane they are traveling towards)
- after ions travel down their [gr], they take the charge with them (increasing (Na+ takes charge inside and depolarises a membrane) or decreasing (K+ takes charge out of cell and hyperpolirezes the membranes) the membrane potential.) In the case of K+, when membrane potential reaches -90 after K+ takes all the charge with itself out of the cell following it’s own [gr], thus hyperpolarizing it, the [gr] at that point will = el.gr and they will be in opposite direction. [Gr] will be taking K+ ions out of the cell and el.gr will be bringing them back because positive K+ will be getting progressively more attracted to the opposite negative charge of the membrane at -90.
- Allows an ion to diffuse across membrane
- Can be 1) Concentration Gradient [gr] diffusion potention
2) Electrical gradient/force diffusion potential
- When [gr] and el.gr are in the same direction => no equilibrium
- When [gr] and el.gr are in the opposite dirn AND of the same magnitute => equilibrium
- Both [gr] and el.gr have the potential to diffuse ions through the membrane. 2 of the them combined produce NET diffusion potention. When the 2 oppose each other - there is no net diffusion potential and when the 2 oppose and are equal in magnitude, you get equilibrium. Got it?
Equilibrium doesn’t always mean =
A tiny change in [ ] of an ion can have huge effect on membrane potential/polarity - it’s good bc this way the body stays in homeostasis and [Na] and [K] stay normal. So at Equilibrium, there is virtually no change in the [ ] of ions on either side of cell and the tiny change in [ ] is corrected by el.gr which brings those ion right back inside. So the mount of ions leaving the cell = the amount of ions coming back into cell. Efflux = influx
E(k)=-90 Equilibrium of K+ = -90
-90 is the potential of the membrane under equilibrium of K+
If see E => use Nerst equation
If see RMP (resting membrane potential) => use Ohm’s
If you increase the amount of open channels (increase the permiability) for a given ion, what will happen to the Equilibrium of that ion?
Nothing, the amount of open channels/permiability does not effect the E. E depends ONLY on [gr]. Simply adding channels without changing [ ] ‘s won’t affect E. (If NT binds to Na+ ligand-gated channel -> opens channels and increases permiability -> increases depolarization of the membrane but E(na) is not changed. E (na) changed when a person has hyponatremia or hypernatremia.
When hypokalemia: level of K+ outside the cell is below the normal [ ]
If normal  falls to  outside while inside remains , then the gradient is increased from 145 to 147 (150-3). Increase in [gr] -> increase in opposing el.gr -> increase in E(k) from -90 to -100 (increase the absolute number first, then add sign back”. Since membrane potential normally lies between Ek=-90 and ENa=+65, now membrane potential is going to be between Ek=-100 and ENa = + 65. Since Ek became more negative (increased), membrane potential will also become more negative (increased from -70). RMP becoming more negative = hyperpolarization.
Primary mechanism that maintains RMP?
Diffusion of ions down concentration gradients through background/leaky channels.
- Na-K ATPase contributes to RMP but not nearly as much (indirect role)