The locus coeruleus is a dark violet spot visible in the anterior part of the "floor" of the fourth ventricle , such a spot on the right side and one on the left. The locus coeruleus contains the concentrated noradrenaline-producing cell group A6.
The stain consists of about 15,000 dark-pigmented noradrenaline-producing nerve cell bodies. The locus coeruleus is practically alone responsible for noradrenaline supply to the entire CNS.
Noradrenergic nerve fibers are mediated by:
1/ the medial forebrain bundle (MFB) up to the large brain
2/ the upper cerebellar arm into the cerebellum where they are considered to have an inhibitory influence on the Purkinje cells and
3/ fasciculus longitudinalis dorsalis down through the brainstem and then on through the entire spinal cord.
The locus coeruleus neuron is among the most branched of all neuron types. So, for example, there are data (ref . 6, p.285) that say that no nerve cell in the cortex of the cerebrum is further away than 30 μm from an end or varicosity belonging to a locus coeruleus neuron!
L. A. Schwartz and L. Luo (2015) Organization of the Locus Coeruleus-Norepinephrine System. Current Biology. Minireview. http://dx.doi.org/10.1016/cub.2015.09.039