Which neurotransmitter is primarily associated with the sympathetic nervous system?

• A. Norepinephrine
• B. Acetylcholine
• C. GABA
• D. Glutamate

Answer: (A)

Sympathetic control of target organs relies mainly on norepinephrine released by postganglionic neurons. This transmitter binds to adrenergic receptors on organs such as the heart, blood vessels, and airways, driving the classic fight-or-flight responses like increased heart rate, vasoconstriction, and bronchodilation. While the preganglionic sympathetic neurons use acetylcholine to activate the postganglionic neuron, the postganglionic neuron’s release of norepinephrine onto the effector tissue is what largely mediates sympathetic effects. An exception is the sweat glands, where acetylcholine is used, but for most organs norepinephrine is the primary transmitter. Acetylcholine is more characteristically associated with the parasympathetic system at the postganglionic synapse, and GABA and glutamate are mainly central nervous system neurotransmitters rather than peripheral mediators of sympathetic activity.