FoundationalConceptsNeuroscience

nine. Specific enzymes catalyze each step in this pathway.

Ventral tegmentum

Substantia nigra

Figure 7.5. Some of the dopaminergic pathways in the brain.

As is the case for acetylcholine and serotonin, the neurotransmit-
ters dopamine, norepinephrine, and epinephrine are associated with
clusters of neurons deep in the interior of the brain, with the numbers
of neurons in these clusters relatively small, on the order of one hun-
dred thousand cells or so. And as before, the axons from these clusters
innervate large regions of the brain, so these neurotransmitters po-
tentially impact billions of other cells in the brain. The dopaminergic
brainstem nuclei include the substantia nigra and ventral tegmentum
(Fig. 7.5).
Nearly all the norepinephrine-producing (noradrenergic) cells in
the brainstem are located in the locus coeruleus, a small nucleus in the
pons (Fig. 7.6). The epinephrine-producing neurons are relatively few