Questions: Autonomic Nervous System: Sympathetic and Parasympathetic
3 questions to test your understanding
Score: 0 / 3
Question 1 Multiple Choice
A student experiences a sudden stressful situation and notices: heart rate increasing, pupils dilating, and digestion slowing. Which ANS division and primary neurotransmitter at the target organ are responsible?
AParasympathetic division; acetylcholine
BSympathetic division; acetylcholine
CSympathetic division; noradrenaline
DSomatic division; noradrenaline
The sympathetic (fight-or-flight) division produces exactly this cluster of responses: increased heart rate to deliver more oxygen to muscles, pupil dilation for wider visual field, and slowed digestion to redirect blood away from the gut. Noradrenaline is the neurotransmitter released by postganglionic sympathetic neurons onto target organs. Acetylcholine is used at the ganglionic synapse (between pre- and postganglionic neurons) in both divisions, but it is not the final effector neurotransmitter for most sympathetic targets.
Question 2 True / False
Both the sympathetic and parasympathetic divisions use acetylcholine as the neurotransmitter at the synapse between the preganglionic and postganglionic neuron (the ganglionic synapse).
TTrue
FFalse
Answer: True
This is a common misconception to test. Many students believe the sympathetic system is 'all noradrenaline' and the parasympathetic is 'all acetylcholine.' In fact, BOTH divisions use acetylcholine at the ganglionic synapse. The distinction is at the target organ: parasympathetic postganglionic neurons release acetylcholine onto their effectors, while most sympathetic postganglionic neurons release noradrenaline. The adrenal medulla is an exception — it releases adrenaline (epinephrine) directly into the bloodstream when stimulated by preganglionic sympathetic fibers.
Question 3 Short Answer
Why is it functionally important that the sympathetic and parasympathetic systems have opposing effects on the same organs, rather than one system simply turning effects on and off?
Think about your answer, then reveal below.
Model answer: Dual, opposing innervation allows fine-grained, continuous control. Rather than binary on/off states, most organs can be precisely tuned by varying the relative activity of both divisions — increasing parasympathetic tone slows heart rate while decreasing sympathetic tone does so differently and at different rates. This antagonistic control gives the nervous system greater dynamic range and faster response times than a single on/off pathway could provide.
Consider heart rate regulation: resting heart rate is maintained by relatively high parasympathetic (vagal) tone holding it below the heart's intrinsic pacemaker rate of ~100 bpm. During exercise, both increased sympathetic activity AND withdrawal of parasympathetic tone contribute to the rise in heart rate — and the response can be graded with precision. This push-pull architecture is a fundamental design feature of homeostatic regulation throughout the body.