At that point K+ voltage gated channels open up in the same section, AcH sterase breaks up AcH and Na+ channels close down. The potential goes past the threshold and then to 35+ve. It also slowly activates the K+ voltage gated channels for the same section. When Na+ gets in, that activates the 'voltage gated Na+ channels in the neighboring section of axon hillock' and they open up. Na+ is not leaking in via leakage channels, it is getting in via facilitated diffusion through AcH. My understanding of action potential goes something like.ġ) AcH is released, binds to the receptor which allows Na+ to get in via facilitated diffusion. I had some confusion regarding this as well so I am just trying to clear it up. Is this only the case if the membrane was completely impermeable to one of the ions? I think the reasoning has to do with the fact that the membrane is slightly permeable to both, however, this still doesn't completely make sense to me. In my head, it makes sense that the concentration gradient might never get established, but if the gradient was already there I feel like there would still be an equilibrium potential. My book states that if the Na-K pump was not present, the concentration gradient would dissipate. The equilibrium potential is reached at the point the concentration gradient is balanced by the developing potential. K tries to flow down its concentration gradient, which develops a 'negative' charge on the inside of the cell. The membrane is relatively very permeable to K and barely permeable to Na.

The classic example is the neuron and Na-K pump. In order to have a membrane potential, there must be a concentration gradient for the ion as well as membrane permeability to that ion.

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