in number and are also found in the vicinity of the locus coeruleus.
The substantia nigra (Latin nigra = dark) and locus coeruleus
(Latin coeruleus, caeruleus = dark blue) are named for the dark color of
their cells—the darkness being due to intracellular accumulation of
melanin, a polymer with components related to dopamine. Melanin
(Greek melas = black, dark) actually refers to a group of chemically
related polymers found in many organisms. Melanin is what gives
human hair and skin its color. One function of melanin in the skin
is to absorb ultraviolet radiation from sunlight, protecting the body
from potential damage. The function of melanin in brain cells (some-
times called neuromelanin) is unknown.
Locus coeruleusFigure 7.6. Some of the noradrenergic pathways in the brain.Acetylcholine and the monoamine neurotransmitters share the
property of being produced by relatively small numbers of neurons
in the interior of the brain that impact the activity of billions of cells