Norepinephrine is best described as?

• A. Hormone released by the adrenal medulla and sympathetic nerves. Binds with adrenergic receptors in the sympathetic nervous system.
• B. Neurotransmitter released by sympathetic neurons; binds to nicotinic receptors only.
• C. Neurotransmitter released by parasympathetic neurons; binds to GABA receptors.
• D. Hormone produced by the pituitary gland; regulates cortisol.

Answer: (D)

Norepinephrine acts as both a neurotransmitter in the sympathetic nervous system and as a hormone released into the bloodstream by the adrenal medulla. When released from sympathetic nerve terminals, it binds to adrenergic receptors (alpha and beta subtypes) on target organs, producing effects such as increased heart rate, vasoconstriction, and pupil dilation. It’s not associated with nicotinic receptors, GABA receptors, or parasympathetic signaling. It also is not produced by the pituitary gland or responsible for regulating cortisol; cortisol regulation involves ACTH signaling to the adrenal cortex. So the best description is that norepinephrine is a neurotransmitter released by sympathetic neurons and a hormone from the adrenal medulla that binds to adrenergic receptors.