I'm really confused by how the terms Hyperpolarization and Depolarization are used in Cell biology and hope somebody can enlighten me hopefully. Here's what they mean for me so far:
Depolarization means the inner and outer side of the cell membrane become less polarized (so the Nernst potential tends to 0 due to log(1) being 0)
Hyperpolarization that the inner and outer side become more polarized (so the Nernst potential increases).
Assuming I'm not completely wrong until here. Let me give some examples, so maybe you can see better where the problem lies:
- We have a model cell so (K+ internal is 140 mmol/l, K+ external is 4.5 mmol/l) and the external side is increased to 8 mmol/l , then a DEPOLARIZATION occurs because
roughly : $-60 \cdot \log(140/4.5) = -90 mV < -60 \cdot \log(140/8) = -74 mV$ ; or in other words, "energy" was used so a depolarization occurred (so far this seems correct with the solutions I can find to this example)
- Now comes the second example (famous depolarization of a cell with the graph and the peak and repolarization):
- Na+ enters the cell : the concentrations im gonna use for this example are inside:$12 mmol/l$ and outside $140 mmol/l$
so before the Na enters we have: $-60 \log(12/140)= 60 mV$
if Na+ enters the Cell, a depolarization should occur (because the difference inside and outside is decreased)
this seems fine with the graph...
the part of the graph which goes over 0 (also called "overshoot"), is it not technically a hyperpolarisation+depolarization?
repolarization: this occurs by K+ ions leaving the cell, but that doesn't make sense according to the Nernst equation?
The concentration inside before the cells leaving is 140, outside 4.5 ; if K+ leave the cell, its simply going to depolarize more... So why does repolarization occur and not depolarization?
It's commonly stated that Hyperpolarization is caused by K+ LEAVING the cell (for example with ion channels) , how does this make sense if the inner concentration is higher than the outer? If anything, this again should lead to depolarization
Same thing with K+ entering the cell, isn't that supposed to cause a hyperpolarization as well?
I appreciate any kind of insight into this matter, since it seems that I'm completely wrong.