system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Where does the brain generate its ‘current’ to send small electrical impulses to muscles etc...?
gpt
There are pumps and gates in your cell membranes, which control the flow of ions. Ions are charged particles (positive or negative), so their movement creates a current and thus electrical impulses.

One example of a pump is the sodium-potassium pump. This pump exchanges 3 Na+ (soidum) ions for 2 K+ (potassium) ions, making the cell lose 1 positive ion each time. This makes the cell more and more negatively charged over time. This effect is slow-ish and mostly constant.

Now we come to the gates. These have a “threshold”, like a plug in a broken dam holding back the water. Once the threshold limit is crossed, everything just bursts through.

In the sodium-potassium example, the sodium gate will open when the cell reaches a certain threshold of negative charge, which will instantly draw the sodium from outside the cell back into the cell to balance the concentration lost by the pump. This causes a massive shift of ions, creating an electrical impulse.

The electrical impulse can also trigger other gates in neighbouring cells to open, causing a “cascade” where the first signal spreads out and travels down the nerves to muscle cells.