Well, there are two facts, two things about calcium that makes them so prevalent. Number one is our cells can actually easily detect even the smallest changes in calcium mine concentrations inside the cell in a cytoplasm. And number two is calcium mines can actually form very strong interactions with proteins. And we'll see why that's important and what that does in just a moment. So let's focus on number one. The smallest changes in cytoplasmic calcium ion concentration can be detected by the cell.