what kind of a structure does this organ have?
Its structure differs from that of epinephrine only in that epinephrine has a methyl group attached to its nitrogen, whereas the methyl group is replaced by a hydrogen atom in norepinephrine.
Norepinephrine
is a catecholamine and a phenethylamine. Its structure differs from that of epinephrine only in that epinephrine has a methyl group attached to its nitrogen, whereas the methyl group is replaced by a hydrogen atom in norepinephrine. 
what role does the neurotransmitter norepinephrine have in the cardiac system It increases heart rate and blood pressure what is norepinephrine? It is an organic chemical in the catecholamine family that functions in the brain and body as a hormone and neurotransmitter.
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Norepinephrine [SEP] Structure
Norepinephrine is a catecholamine and a phenethylamine. Its structure differs from that of epinephrine only in that epinephrine has a methyl group attached to its nitrogen, whereas the methyl group is replaced by a hydrogen atom in norepinephrine. The prefix "nor-" is derived as an abbreviation of the word "normal", used to indicate a demethylated compound.