What is parkinsonism caused by?

Parkinsonism primarily results from the degeneration of dopamine-producing neurons in the substantia nigra, a critical area of the brain involved in movement control. When these neurons die or become impaired, there is a significant decrease in dopamine levels, leading to the characteristic motor symptoms associated with Parkinson's disease and other forms of parkinsonism, such as tremors, rigidity, and bradykinesia (slowness of movement).

Understanding the role of the substantia nigra is crucial for grasping the underlying pathophysiology of parkinsonism. The loss of dopamine not only affects motor control but also influences various neural circuits that contribute to mood, cognition, and autonomic functions, further complicating the clinical picture for affected individuals.

Other factors, such as genetic mutations and environmental toxins, can contribute to parkinsonism but are not the primary cause. While infections in the brain may lead to other neurological issues, they typically do not cause the sustained degeneration seen in parkinsonism. Therefore, the direct link between cell death in the substantia nigra and the development of parkinsonism firmly justifies why this answer is the correct choice.