Introduction

Parkinson's disease (PD) is a slowly progressive disorder that affects movement, muscle control, and balance. Parkinson's disease is referred to as idiopathic, which means that the cause is unknown. This term distinguishes the primary disease from parkinsonism, which are the symptoms occurring from a known cause. In addition to its effects on motor control, Parkinson's disease is now recognized as a broader condition that can include cognitive and behavioral disturbances, sleep disorders, speech difficulties, and other problems.

Parkinson's Disease and Dopamine Loss

Parkinson's disease occurs from the following process in the brain:

• PD develops as cells are destroyed in certain parts of the brain stem, particularly the crescent-shaped cell mass known as the substantia nigra.

Parkinson's disease is a slowly progressive disorder that affects movement, muscle control, and balance. Part of the disease process develops as cells are destroyed in certain parts of the brain stem, particularly the crescent-shaped cell mass known as the substantia nigra. Nerve cells in the substantia nigra send out fibers to tissue located in both sides of the brain. There the cells release essential neurotransmitters that help control movement and coordination.

• Nerve cells in the substantia nigra send out fibers to the corpus stratia, gray and white bands of tissue located in both sides of the brain.
• There the cells release dopamine, an essential neurotransmitter (a chemical messenger in the brain). Loss of dopamine in the corpus stratia is the primary defect in Parkinson's disease.

Dopamine. Dopamine deficiency is the hallmark feature in PD. It is one of three major neurotransmitters known as catecholamines, which help the body respond to stress and prepare it for the fight-or-flight response. Loss of dopamine negatively affects the nerves and muscles controlling movement and coordination, resulting in the major symptoms characteristic of Parkinson's disease. Dopamine also appears to be important for efficient information processing, and deficiencies may also be responsible for problems in memory and concentration that occur in many patients.

Although it is clear that dopamine deficiency is the primary defect in Parkinson's disease, it is not clear what causes dopamine loss. The culprit is less likely to be a single cause than a combination of genetic and biologic factors, which are triggered by some environmental assault.

Other Changes. The PD disease process also appears to impair nerve endings in the heart, causing dysautonomia-- changes in the autonomic (also called sympathetic) nervous system. Such changes may impair the release of norepinephrine, a hormone that regulates blood pressure, pulse rate, perspiration, and other automatic responses to stress. Evidence suggests this may be responsible for the abrupt drops in blood pressure when standing that occur in PD. Further research is underway to determine if the loss of nerve terminals is confined to the heart or if it affects other organs as well.

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