Now, the cell that is sending that electrical signal is our presynaptic cell. The cell that is receiving that signal, in this case, it's the muscle cell. This is known as the post synaptic cell. So let's discuss what actually takes place during this process. So, as soon as the action potential comes to our synaptic terminal, it causes the calcium channels on the membrane to open up. As soon as our calcium channels open up, that will cause the influx of calcium ions into the cell.