While this second brain is not nearly as complex as the brain in your head, it does have its own motor and sensory neurons, and it uses many of the same brain chemicals and neurotransmitters. It even grows from the same part of the embryo that your other brain grows from. What Does This Second Brain Do? Mostly, it coordinates the chemical and muscular activity of digestion–a process that’s actually quite complicated. It also responds to messages from your other brain–especially messages about fear or danger. If you get a stomach ache or diarrhea because of stress or fear, it’s this second brain that coordinates that. So the next time you put on your thinking cap, remember to put on a sweater as well!