Answer :
Upon reaching the threshold for an action potential, the next step in its generation is the opening of _sodium (Na)_ channels. The correct answer is sodium,
How does membrane depolarization occur?
The occurrence of action potential requires the existence of active voltage-dependent channels to open and close in response to the membrane depolarization.
When depolarization reaches and supers the threshold point, voltage-dependent Na+ channels open and the ion gets into the cell.
The entrance of Na+ decreases the electric charge difference between the cellular interior and exterior. Membrane depolarizes and produces the action potential that tends to reach a potential equilibrium for Na+ = +60mV.
The higher the Na+ input is, the greater is the depolarization and the greater is the Na+ permeability.
Once Na+ channels are closed, voltage-dependent K+ channels open, increasing the membrane permeability to the ion, letting K+ get out of the cell, following the electrochemical gradient.
The closure of Na+ channels and opening of K+ channels are responsible for membrane repolarization.
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