This document discusses neurodegenerative disorders like Parkinson's disease, Huntington's disease, and Alzheimer's disease. It describes how Parkinson's disease results from the loss of dopaminergic neurons in the substantia nigra pars compacta. The history of Parkinson's disease is discussed, with James Parkinson first describing it in 1817. The clinical features of Parkinsonism including tremor, rigidity, and hypokinesia are also summarized.