The chemical compound norepinephrine (NC8O3H11), also known as noradrenaline, is a catecholamine neurotransmitter hormone released from the adrenal glands that affects parts of the human brain where attention and impulsivity are controlled. This compound affects the fight-or-flight response, activating the sympathetic nervous system to directly increase heart rate, release energy from fat and increase muscle readiness.
The host of physiological changes activated by a stressful event are unleashed in part by activation of a nucleus in the brain stem called the locus ceruleus. This nucleus is the origin of most norepinephrine pathways in the brain. Neurons using norepinephrine as their neurotransmitter project bilaterally from the locus ceruleus along distinct pathways to the cerebral cortex, limbic system, and the spinal cord, among other projections.
Norepinephrine is synthesized by a series of enzymatic processes in the adrenal medulla that convert tyrosine first Dihydroxyphenylalanine (DOPA), then to dopamine, which is then biosynthesized into norepinephrine. Some norepinephrine may then be further converted to epinephrine.