Norepinephrine and epinephrine have dual functions as hormones and neurotransmitters. They play a part in the fight-or-flight response. Norepinephrine is produced by certain neurons as well as the adrenal glands, but epinephrine is only produced by the adrenal glands. Norepinephrine is a psychoactive molecule in the brain, promoting blood circulation to the skeletal muscles. Epinephrine is not a psychoactive compound, but increases energy production via glucose release in response to rising norepinephrine levels. It also relaxes muscles to dilate the bronchial tubes and allow increased oxygen intake. Epinephrine and norepinephrine were called adrenaline and noradrenaline until the brand name Adrenaline was registered by a drug company. Somewhat confusingly, neurons releasing norepinephrine are still called “noradrenergic” and those releasing epinephrine “adrenergic”.

Norepinephrine projections emanating from the locus coeruleus in the brainstem.