Is there a electricity inside the human body? What creates the spark when you shake hands with a person?
There definitely is!
There are a lot of things going on when one person reaches out to touch something, but the underlying action potential that causes the contraction of several muscles is stimulated by an increase in calcium ion concentration. This allows tetany to occur, which is a high frequency of action potential.
This can be taken much further by evaluating how the calcium is related (it gets the energy from ATP), which may mean that glycolysis and/or aerobic respiration is the "spark." In reality, these processes (along with hundreds more) are all occurring simultaneously and none should be reasonably singled out as the spark.
If I had to identify one, though, I'd say it's the release of calcium through what is known as the SERCA: