Which neurotransmitters are associated with the Sympathetic Nervous System in smooth muscle?

The sympathetic nervous system primarily uses norepinephrine and epinephrine as its key neurotransmitters for signaling in smooth muscle. Norepinephrine is released from sympathetic postganglionic fibers and binds to adrenergic receptors on the target smooth muscle cells, leading to various physiological responses such as vasoconstriction or relaxation of bronchial passages, depending on the receptor subtype engaged.

Epinephrine, primarily released from the adrenal medulla into the bloodstream, acts similarly to norepinephrine but can influence a broader range of tissues due to its systemic circulation. It enhances the stress response by increasing heart rate and redirecting blood flow to essential organs, among other effects.

Dopamine, while it has a role in the nervous system, is not typically associated with the direct signaling mechanisms of the sympathetic nervous system in smooth muscle contraction or relaxation. Therefore, the inclusion of norepinephrine and epinephrine as primary neurotransmitters makes this the correct choice for this question.