Caffeine affects our body by increasing autonomic arousal, specifically the activity of the sympathetic arm of the autonomic nervous system. This is essentially the alertness arm of your nervous system, creating a sense of readiness in your brain and body. It does this by activating the sympathetic chain ganglia, which run from about the base of your neck to the top of your pelvis. This activation releases a bunch of chemicals into your body, including adrenaline, which also increases in your brain, creating a state of alertness and readiness. This heightened state can bias our brain and body systems toward action as opposed to inaction, which can increase impulsivity.