Which neurotransmitter is primarily used by sympathetic postganglionic fibers?

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

Answer: (D)

In the sympathetic division, the postganglionic neurons typically release norepinephrine onto target organs, where it binds to adrenergic receptors (alpha and beta) to produce the characteristic fight-or-flight responses. The preganglionic neurons release acetylcholine to activate the postganglionic neurons, but the transmitter released at the organ is norepinephrine. An important exception is the sweat glands, which receive sympathetic fibers that release acetylcholine. The other options don’t fit because dopamine and GABA aren’t the primary transmitters used by sympathetic postganglionic fibers, and acetylcholine is the transmitter for parasympathetic postganglionic fibers and, in some sympathetic pathways (like sweat glands), for specific targets.