system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does your brain automatically know how to make your entire body function?
gpt
Basic bodily functions like breathing and heart beat are plain hardwired in to your body. Just like simple electrical circuits. Yes, there are things (hormones) that can regulate them up or down, and your concious brain can override the signals. But evolution has conserved this feature because it is so efficient at keeping animals alive. 

Your heart beat for example is controlled by the "sino-artial node". It is basically an electrical timer that self regulates it's electrical pulses, and doesn't even need input from your brain to keep your heart going (hence why you can be brain dead, but still "alive").