The sympathetic nervous system (SNS) is responsible for arousal, including the fight-or-flight response (Darwin’s “escape or avoidance behavior”). Almost two thousand years ago the Roman physician Galen gave it the name “sympathetic” because he observed that it functioned with the emotions (sym pathos). The SNS moves blood to the muscles for quick action, partly by triggering the adrenal glands to squirt out adrenaline, which speeds up the heart rate and increases blood pressure.
The second branch of the ANS is the parasympathetic (“against
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