what is norepinephrine?
It is an organic chemical in the catecholamine family that functions in the brain and body as a hormone and neurotransmitter.
Norepinephrine
is an organic chemical in the catecholamine family that functions in the brain and body as a hormone and neurotransmitter. 
what role does the neurotransmitter norepinephrine have in the cardiac system It increases heart rate and blood pressure
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Norepinephrine [SEP] Introduction
Norepinephrine (NE), also called noradrenaline (NA) or noradrenalin, is an organic chemical in the catecholamine family that functions in the brain and body as a hormone and neurotransmitter. The name "noradrenaline", derived from Latin roots meaning "at/alongside the kidneys", is more commonly used in the United Kingdom; in the United States, "norepinephrine", derived from Greek roots having that same meaning, is usually preferred. "Norepinephrine" is also the international nonproprietary name given to the drug. Regardless of which name is used for the substance itself, parts of the body that produce or are affected by it are referred to as noradrenergic.