The system that runs without you
The autonomic nervous system runs the housekeeping you never think about: heartbeat, blood pressure, sweating, pupil size, digestion, bladder. You don't decide to do these things — your nerves do, quietly, all day. Almost every drug in this track works by nudging that machinery, so it pays to know the layout before we touch a single pill.
Think of it as two opposing teams sharing the same field. The sympathetic nervous system is the fight-or-flight team: it speeds the heart, opens the airways, widens the pupils, and shunts blood to muscle. The parasympathetic nervous system is the rest-and-digest team: it slows the heart, narrows the pupils, and turns up digestion. Most organs feel both, so the resting state is a tug-of-war, not an on/off switch.
Two chemical languages
Nerves don't touch their targets — they speak across a tiny gap using a chemical messenger, a neurotransmitter. The autonomic system uses mostly two: acetylcholine and norepinephrine. A handy first rule: parasympathetic nerves release acetylcholine at the organ (they are *cholinergic*), while most sympathetic nerves release norepinephrine at the organ (they are *adrenergic*).
Why one drug touches many organs
Because the same messenger talks to many organs, a drug aimed at one effect often produces several. A drug that blocks acetylcholine to calm an overactive bladder may also dry the mouth, blur near vision, and speed the heart — these are side effects, and in the autonomic system they are highly predictable once you know which target the drug hits. That predictability is the whole point of this track: learn the wiring once, and the side effects almost write themselves.