Hi huys, I have a problem with this statement: "Action potentials are formed when a stimulus causes the cell membrane to depolarize past the threshold of excitation, causing all sodium ion channels to open."
Isn’t the cell membrane depolarized BECAUSE the ion channels open?
I think you are correct (or more precisely when the Na+ channels open since the K+ open later). There is a threshold voltage that switches the state of what I found to be a flip-flop. The circuit is also called a "monostable multivibrator".