Causes:
Primary Parkinson's Disease
This scenario is the most common form of Parkinson's and is experienced in the majority of cases.
In the early stages of Primary Parkinson's Disease, brain nerve cells located at the substantia nigra, locus caeruleus, and other brain stem dopaminergic cell groups are lost. The decreased number of substantia nigra neurons results in depletion of the chemical neurotransmitter dopamine, which transmits nerve signals as electrical impulses along and between nerve pathways, from and to muscles.
The basal ganglia, located deep within your brain, is responsible for smooth movement and posture coordination. The main neurotransmitter of the basal ganglia is dopamine, which is used to communicate with the thalamus and relays the processed information back to the cerebral cortex, resulting in a coordinated movement. Under Parkinson's disease, nerve cell degeneration is localized in this area, leading to lower dopamine production and a reduced number of connections between nerve cells and muscles.
With the connections severed, the above-mentioned symptoms and signs occur. As degeneration continues and muscle control is lost, symptoms increase.
The exact cause of nerve cell degeneration and resulting decreased dopamine production is not known.
A number of theories hold that excess nerve cell exposure to free radicals and their damaging effects can lead to the development of Parkinson's (making antioxidant supplementation an essential component of any Parkinson's healing protocol). Once the disease is established, it generates peroxynitrite, a highly toxic free radical in the body. This results in an unfortunate positive feedback where degeneration leads to additional degeneration, accelerating the cumulative effect of damage.
Secondary Parkinsonism
Under Secondary Parkinsonism, the action of dopamine on nerve cells is interfered with and dopamine receptors are blocked, resulting from the administration of antipsychotic drugs used to treat schizophrenia and severe paranoia. N-MPTP (n-methyl-1,2,3,4-tetrahydropyridine), a street-form of opium synthesized from meperidine can lead to severe and irreversible Parkinson's in intravenous drug users.
Postencephalitic Parkinsonism
Postencephalitic Parkinsonism is caused by viral encephalitis -- a rare and sever flu-like infection that causes brain inflammation and results in forced, sustained deviation of the head and eyes, among other effects.
Other Causes
Other causes of Parkinson's disease include blood-vessel disorders such as atherosclerosis and stroke, carbon monoxide or manganese poisoning, hydrocephalus, hypoparathyroidism, Shy-Drager syndrome, and other degenerative brain diseases or conditions that lead to reduced dopamine production.
Genetics
Though it is not believed that genetics play a significant factor in developing Parkinson's disease, it does tend to run in families. One third to one quarter of people dealing with Parkinson's have a family history of the disease. The risk is further increased if the father had Parkinson's. Keep in mind that risk factors merely statistically increase the risk and are not a cause in themselves.
