 The most important source of norepinephrine in the brain is the locus coeruleus , which contains noradrenergic cell group A6 and adjoins cell group A4 . The locus coeruleus is quite small in absolute terms — in primates it is estimated to contain around 15 @,@ 000 neurons , less than one millionth of the neurons in the brain — but it sends projections to every major part of the brain and also to the spinal cord . 
