What neurotransmitter is most associated with the sympathetic nervous system?

• A. Dopamine
• B. Acetylcholine
• C. Norepinephrine
• D. Serotonin

Answer: (C)

The main idea is that the sympathetic division uses norepinephrine as its primary messenger at the usual postganglionic synapses onto target organs. In this system, preganglionic neurons release acetylcholine to activate the postganglionic neuron, which then releases norepinephrine onto the organs to produce the fight-or-flight effects (like increased heart rate, dilated airways, and ramped-up blood flow to muscles). The organs respond through adrenergic receptors that are designed to pick up norepinephrine. There are a couple of notable exceptions to keep in mind: sweat glands are an exception where acetylcholine acts as the postganglionic transmitter, and the adrenal medulla releases epinephrine (and some norepinephrine) directly into the bloodstream, amplifying the sympathetic response. But overall, norepinephrine is the neurotransmitter most associated with sympathetic postganglionic signaling.