Autonomic nervous system
MCAT glossary · Biological & Biochemical Foundations of Living Systems
Definition
Sympathetic (fight-or-flight, NE/E) vs parasympathetic (rest-and-digest, ACh); enteric nervous system controls gut.
Autonomic nervous system in plain English
This is the part of your nervous system that runs your body on autopilot — heartbeat, digestion, sweating — without you thinking about it. It has two main modes that push against each other: the sympathetic branch is the "fight-or-flight" gas pedal (it speeds your heart and floods you with adrenaline when you're scared), and the parasympathetic branch is the "rest-and-digest" brake (it calms you down and helps you digest afterward). There's also a third crew, the enteric nervous system, which is a mini-brain wrapped around your gut that manages digestion largely on its own. Different chemical messengers carry these signals — noradrenaline/adrenaline for the gas, acetylcholine for the brake.
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