What neurotransmitter is released by post-ganglionic sympathetic fibers?

Post-ganglionic sympathetic fibers primarily release norepinephrine as their neurotransmitter. This is fundamental to the sympathetic division of the autonomic nervous system, which is responsible for the body's 'fight or flight' responses. When the sympathetic fibers activate, they facilitate various physiological changes, such as increased heart rate, bronchodilation, and enhanced blood flow to skeletal muscles. Norepinephrine binds to adrenergic receptors on target organs, triggering these responses.

The other neurotransmitters listed, such as acetylcholine, are typically associated with the parasympathetic nervous system. While some sympathetic fibers, particularly those innervating sweat glands, do release acetylcholine, the majority utilize norepinephrine. Dopamine and serotonin are involved in other neurological pathways and do not play a significant role in the neurotransmission of post-ganglionic sympathetic fibers. Understanding this distinction is crucial for grasping how the autonomic nervous system regulates various bodily functions.