Pathology of Parkinson’s: How the Disease Arises and Progresses
Parkinson’s disease is a progressive neurological disorder that affects the lives of more than 12 million people worldwide. It gradually advances in the body, and as brain cells degenerate, it causes multiple problems—most notably motor disturbances. However, Parkinson’s symptoms extend far beyond movement difficulties and can influence many aspects of a patient’s daily life. To better understand why Parkinson’s occurs, we need a closer look at brain structure, the role of certain neurotransmitters, and the factors that initiate this process.
Symptoms and Effects on the Body
Parkinson’s manifests with motor symptoms such as tremor of the hands or body, muscle rigidity, slowness in everyday tasks like buttoning clothes or walking, and postural instability. But that’s only part of the story. Many patients face reduced facial expressiveness, swallowing difficulties, reduced vocal strength and volume, blurred vision, trouble opening the eyelids, or a shuffling gait with short steps and freezing at movement initiation. In addition, the disease can disrupt sleep, alter mood, and even lead to depression or anxiety—evidence of its broad impact on both body and mind.
The Disease Roots in the Brain
The origin lies in a region called the basal ganglia, a control center that coordinates movement and communicates with the cerebral cortex (which plans decisions and movements) and the thalamus (which smooths and integrates movements). At the core of the basal ganglia is the substantia nigra, which plays a crucial role. It contains specialized neurons that produce dopamine. Dopamine acts as a messenger, helping the brain finely tune movement, generate pleasure, and reinforce motivation. It is produced by neurons and transmits signals by binding to specific receptors in the brain.
Under normal conditions, dopamine modulates two main motor pathways. The direct pathway helps make movements faster and stronger (e.g., when switching from walking to running). The indirect pathway prevents excessive slowing of movement (e.g., when coming to a smooth stop after running). The balance between these pathways ensures fluid, coordinated movement.
What Happens in Parkinson’s?
In Parkinson’s disease, the progressive death of dopamine-producing neurons in the substantia nigra reduces dopamine levels in the brain. This reduction disrupts the balance between the direct and indirect pathways. The direct pathway weakens and no longer supports movement effectively, while the indirect pathway becomes overactive. As a result, the motor cortex—responsible for executing movements—becomes less active. This imbalance leads to bradykinesia, incoordination, and difficulty with routine actions such as rising from a chair or walking.
Typically, by the time a person seeks medical attention, about 70% of the dopamine-producing neurons have already been lost. In early stages, residual dopamine stores mask symptoms, but as these reserves decline, signs gradually emerge and the disease progresses.
The Role of Other Neurochemicals
Although dopamine loss is the hallmark of Parkinson’s, other neurotransmitters are involved. Acetylcholine, which supports fine motor control and coordination, may be reduced, while serotonin, which affects mood and sleep quality, can become dysregulated. These changes help explain why patients face not only motor problems, but also sleep disturbances, mood changes, depression, and anxiety.
Risk and Protective Factors
The exact cause of Parkinson’s remains unclear, but several factors may contribute. Family history (genetics) increases risk slightly. Environmental toxins such as pesticides and certain chemicals may also raise risk. On the other hand, some habits appear protective: coffee consumption, smoking (despite its overall harms, it seems specifically protective here), regular exercise, and use of nonsteroidal anti-inflammatory drugs like ibuprofen may be associated with reduced risk.
In Summary
Parkinson’s begins with degeneration of dopamine-producing neurons in the substantia nigra and a disruption of balanced motor pathways. This process affects movement and, through involvement of other neurotransmitters like acetylcholine and serotonin, leads to broader symptoms such as sleep and mood disorders. Although the disease is progressive, understanding these mechanisms and risk factors can aid better management and improve patients’ quality of life.