Which brain region is the primary source of norepinephrine?

• A. Locus coeruleus
• B. Raphe nuclei
• C. Substantia nigra
• D. Hypothalamus

Answer: (A)

Norepinephrine in the brain comes primarily from neurons in the locus coeruleus, a small cluster located in the dorsal pons. These neurons project widely throughout the brain—into the cortex, limbic system, and spinal cord—allowing norepinephrine to modulate arousal, attention, and the stress response. The raphe nuclei are the main source of serotonin, the substantia nigra and nearby ventral tegmental area produce dopamine, and the hypothalamus regulates autonomic and endocrine functions. Because the locus coeruleus houses the majority of CNS norepinephrine–producing neurons and sends widespread projections, it is the principal origin of norepinephrine in the brain.