Practice question · Multiple choice
The sympathetic branch speeds the heart and slows digestion; the parasympathetic does the reverse. Why would evolution couple those two effects together in each branch rather than controlling each organ independently?
Hints
- Ask what a body actually needs during an emergency, organ by organ.
- One signal, many organs. What does that buy you when speed matters?
Show the answer
B. Because the two branches serve coherent whole-body situations.
Why
The situations an animal faces are whole-body situations: escaping a predator needs a raised heart rate, dilated airways, blood at the muscles, and digestion and repair all deferred, so wiring them to one switch reconfigures everything on a single signal. The design predicts its own failure mode: deferring immunity and repair is reasonable for two minutes and ruinous for months.
Practise The Nervous System
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