What is the primary physiologic postganglionic sympathetic neurotransmitter?

What is the primary physiologic postganglionic sympathetic neurotransmitter?

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

Answer: (B)

The key idea is that in the sympathetic division, the postganglionic neuron most often uses norepinephrine to communicate with its target tissues. After the preganglionic neuron releases acetylcholine and activates the postganglionic neuron, that postganglionic fiber typically releases norepinephrine onto adrenergic receptors in organs like the heart, blood vessels, and airways. This norepinephrine binding produces classic sympathetic effects: increased heart rate and contractility, vasoconstriction in many vascular beds, and bronchodilation, among others. There are exceptions to keep in mind: some sweat glands use acetylcholine at the postganglionic level, and the adrenal medulla releases epinephrine (and some norepinephrine) into the bloodstream in response to sympathetic stimulation, acting more as hormones than as direct postganglionic neurotransmitters. Acetylcholine is the primary transmitter in parasympathetic postganglionic fibers, not sympathetic ones, and dopamine isn’t the main transmitter for sympathetic postganglionic signaling. So, norepinephrine is the primary physiologic postganglionic sympathetic neurotransmitter.

The key idea is that in the sympathetic division, the postganglionic neuron most often uses norepinephrine to communicate with its target tissues. After the preganglionic neuron releases acetylcholine and activates the postganglionic neuron, that postganglionic fiber typically releases norepinephrine onto adrenergic receptors in organs like the heart, blood vessels, and airways. This norepinephrine binding produces classic sympathetic effects: increased heart rate and contractility, vasoconstriction in many vascular beds, and bronchodilation, among others.

There are exceptions to keep in mind: some sweat glands use acetylcholine at the postganglionic level, and the adrenal medulla releases epinephrine (and some norepinephrine) into the bloodstream in response to sympathetic stimulation, acting more as hormones than as direct postganglionic neurotransmitters. Acetylcholine is the primary transmitter in parasympathetic postganglionic fibers, not sympathetic ones, and dopamine isn’t the main transmitter for sympathetic postganglionic signaling.

So, norepinephrine is the primary physiologic postganglionic sympathetic neurotransmitter.