The explanation I’ve heard is that we can move because our muscles expand and contract. But then I don’t know how they do that. It feels to me like the answer I hear about how I can move is “smaller things that you are made from move and it makes you move”. I would like to understand on a fundamental level how this process works. I want to know what the smallest component of that process does that results in me being able to do something like type on a keyboard. Thanks.
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The actual physical movement comes from a protein called [actin](https://en.wikipedia.org/wiki/Actin). Like many biological molecules, actin has sites on its surface that can bind to ATP, the energy-storage molecule used by all living things. When ATP binds to those sites, it gets broken apart, and in the process it changes the shape of the actin molecule.
The body regulates this process by controlling the chemical environment around the fibers. Under normal circumstances, the actin is bound to other substances, but flooding the area with calcium ions frees it up to interact with ATP.
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