Final answer:
Parkinson's disease is a nervous system disease characterized by shaking, balance difficulties, and muscle rigidity, caused by loss of dopamine-producing neurons in the substantia nigra.
Step-by-step explanation:
Parkinson's disease is a degenerative disorder of the central nervous system that primarily affects the muscular system and movement. This condition includes symptoms such as constant shaking, difficulty maintaining balance while walking, muscle rigidity, and slowness of movement. Parkinson's disease is classified as a nervous system disease (C), as it is caused by the loss of dopamine neurons in the substantia nigra of the midbrain, which disrupts motor control. Depression and dementia are also common in advanced stages of the disease.