Where does the sodium potassium release potassium ions?

Answer 1

The "fast" voltage-gated sodium channels open at -55 mV and close at about +60 mV. I found your question by attempting to find an answer to its second part which is "when [do]...potassium channels open..." and I have yet to find the answer to this myself! There are lots of graphs in physiology books which indicate it is at a voltage very close to that of the sodium channel but I have yet to find an actual figure! The important thing to know is that the potassium channels open at a similar time but are much slower at allowing potassium to flow out of the cell. The effect is that the influx of sodium rapidly brings the resting membrane potential from it's threshold potential of -55 mV to its peak of about +60 mV, at which point they close and become refractory. The slower potassium efflux then "catches up" and brings the membrane potential back down towards its resting value and actually causes a small over-shoot known as hyperpolarisation. The net change in cytosol concentration of the ions is minimal and quickly reversed by the magnificent Sodium-Potassium-ATPase. If you come across the answer to the opening voltage of the potassium channels, please let me know!

Answer 2

In a neuron, once threshold is reached, voltage gated sodium channels open to depolarize the cell. Then they quickly close while the slowly-opening potassium channels open. When the potassium channels close, relative refractory period begins (the time when another action potential can be fired, but only with a greater stimulus).

Answer 3

Sodium (Na+) is released on the outside of the cell. Potassium (K+) is released on the inside of the cell. This process is called the Sodium-Potassium Pump.