This may end up in GD, but is just a question for now:
If my brain controls my body, what controls my brain?
IOW, if my brain is an interface to my body, what is interfaced to my brain?
What controls my brain?
My testacles, of course.
Chemical reactions and electrical impulses, generally due to the catalyst of sensory perceptions. In other words, the things that you see, hear, smell, feel or taste trigger chemical reactions and electrical impulses in the brain. These reactions and impulses are sometimes translated into thoughts which may in turn translate into actions. In the case of involuntary functions, like heartbeat, the reactions and impulses are translated directly to action, bypassing the thought process.
Of course, some people tend toward the latter for most of their actions.
Well, your terminology is kind of odd. Your brain doesn’t interface your body any differently from how your hand interfaces your arm. Your brain is just another organ, like your pancreas, kidneys or stomach. Only instead of digesting food or purifying blood, it controls muscles, processes sensory input, and maybe occasionally thinks.
What controls your brain? Simple. The laws of physics and chemistry.
Want a more complete explanation? Ok, here’s a whole book worth: How the Mind Works by Steven Pinker.