So, in the interest of determining what it is that we agree upon, with respect to the first premise- We both agree that the particular movement of the hand that we are addressing is something that was not happening before and then it was happening. You say:
"The nerve impulses in the muscles cause the movement of the hand to happen."
This statement contains a notion of a cause and an effect. The only part of this statement we disagree with you on is the cause. So, let us realize that we have agreement on the effect and we happen to have labeled that effect as "beginning to exist." We only labeled it that for convenience's sake, because it describes in plain english the notion we are trying to get across. If you disagree with those words because you think we're being sneaky and implying some other meaning in that label, then we can happily name it something else.
To sum up, we have this phenomenon that we both agree upon, you considering it the effect of the nerve impulses in the muscles, and we reserving judgement on whether it has a cause or not, and we can call this phenomenon "blahblah" (verb).
So we can agree on the first premise as-
1. This particular movement of my hand is something which blahblahed.
And then we can continue to the second premise.