Point 20
Intro
The substantia nigra is thought to be the lesion site in PARKINSON'S disease or paralysis agitans. In this disease there is muscular rigidity, a fine tremor at rest (resting tremor), akinesia or bradykinesia and a slow and shuffling gait. You do not have to worry about the laterality (right or left) of these deficits at this time. The most consistent pathological finding in Parkinson's disease is degeneration of the melanin-containing cells in the pars compacta (another part is called the pars reticulata) of the substantia nigra (melanin is an inert by-product of the synthesis of dopamine). As mentioned above, cells within the nigra produce dopamine normally. This substance passes--via axoplasmic flow--to the nerve terminals in the striatum (caudate nucleus and putamen), where it is released as a transmitter. It is the absence of this transmitter that produces the crippling disorder called Parkinson's disease.