Pathophysiology refers to changes in the normal biochemical, mechanical and physical processes of the body. The pathophysiology of Parkinson's disease refers to physical and biochemical changes in the brain, which in turn produce visible abnormal mechanical and physical functioning throughout the rest of the body. The characteristic tremors associated with Parkinson's disease are an example of this. Although influencing and contributory factors may differ between early onset, juvenile and standard Parkinson's disease, the pathophysiology of Parkinson's is predominantly the same.
Deep within the brain lies a cluster of structures known as the basal ganglia, which translates as “basement structures" and includes the globus pallidum internus, the putamen, and the caudate nucleus. These structures are partly responsible for controlling voluntary movement. Next to the basal ganglia lies the substantia nigra, an area of the brain containing nerve cells that produce the chemical dopamine. Dopamine is a neurotransmitter that relays messages or signals between nerve cells.
The corpus striatum are gray and white bands of tissue that lie within the caudate nucleus and the putamen and are connected to the substantia nigra. The dopamine produced in the substantia nigra is transmitted along the connecting tissue and released into the corpus striatum. This process is essential for smooth, controlled, coordinated and voluntary muscle movement.
Parkinson's disease is an impairment of dopamine production, which results in reduced and ineffective neurotransmission, or message transmission, between the brain cells. It causes the nerve cells to fire erratically and inappropriately, resulting in uncontrolled, involuntary movement and muscle rigidity. The pathophysiology of Parkinson's begins with the death or impairment of dopamine-producing cells in the substantia nigra.
The pathophysiology of Parkinson's is also characterized by the presence of Lewy bodies in the brain, specifically in the substantia nigra. Lewy bodies are abnormal protein structures found in the brain. They are a hallmark of Parkinson's disease and contain the amino acid protein a-Synuclein. In a normal state at normal levels, the function of this protein is to regulate the activity of dopamine transporters. At abnormal levels or in a mutated condition, such as in Lewy bodies, it will contribute to cell death and dysfunction.
Both Lewy bodies and a-Synuclein are important to the pathophysiology of Parkinson's when it occurs in people under the age of 40, and in hereditary cases. Two mutations of a-Synuclein have been identified in early onset hereditary cases of Parkinson's. In cases of Parkinson's with symptom onset past age 60, the pathophysiology includes are-related cell death. It is estimated that up to 13 percent of dopamine-producing neurons die for every decade of life. This means that more cases of age-related Parkinson's will occur as people live longer because, by age 80, a person may have lost from 80 percent to 90 percent of his dopamine-producing cells. Not everyone will lose this many cells or develop Parkinson’s.