Autonomic Nervous System
The Autonomic Nervous System is made up of three parts: the sympathetic nervous system, the parasympathetic nervous system, and the enteric nervous system. It controls the muscles that move involuntarily, like the eyes, the heart, and the intestines. It contributes to the "fight or flight" response, causing your heart to race and your blood pressure to go up when you face danger. This is the system affected by caffeine, which is why caffeine can cause increased heart rate and alertness beyond your control.