How do the mind and body interact?

The body is a physical object whereas the mind is not. Our mind controls our body, sending commands to the brain to move our hand, walk, etc. However, it is like new energy is created when our mind is able to make our brain do something. SOMETHING happens in the brain to tell our arm to move. Chemical change or movement or whatever… but how did something non-physical cause that to happen? I know the brain sends the commands to our arm to make it move… I’m fine with that. But how did the mind send the commend to the brain in the first place?