Action tremor: Rhythmic, involuntary movement of a limb when movement is initiated (for example, when writing or lifting a cup). Not usually seen in the earlier stages of Parkinson's disease.
Adrenaline (epinephrine): A hormone secreted from the adrenal glands (which sit atop the kidneys) in moments of crisis. It stimulates the heart to beat faster and work harder, increases the flow of blood to the muscles, causes an increased alertness of mind, and produces other changes to prepare the body to meet an emergency. Adrenaline also acts as a chemical messenger in the brain to transmit signals between nerve cells.
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Agonist: A chemical or drug that turns on or activates a particular part of a cell that regulates it activity (receptor). For example, dopamine agonists used in the treatment of Parkinson's disease activate the dopamine receptors in the brain, resulting in improvement in symptoms.
Akinesia: Absence or difficulty in producing movements.
Alpha-Tocopherol: A biologically active form of vitamin E.
Amantadine: A drug that improves the symptoms of Parkinson's by increasing the amount of a brain chemical called dopamine. Amantadine can reduce the involuntary movements of Parkinson's disease by acting on other brain chemicals as well.
Anticholinergic: A substance, usually a medication that halts the actions of a chemical that transmits signals between nerves called acetylcholine. The side effects include blurred vision and dry mouth.
Anticholinergic drugs (Artane, Cogentin): The group of drugs that decreases the action of the nerve chemical acetylcholine. These drugs may help reduce rigidity, tremor, and drooling in Parkinson's.
Antihistamines: Drugs opposing the actions of the chemical histamine and commonly used to treat allergies. In the past, these drugs were used to treat some of the symptoms of Parkinson's.
Apomorphine: A drug used to treat severe Parkinson's. It is a form of morphine that can increase the amount of dopamine available in the brain, thereby decreasing symptoms of Parkinson's.
Ataxia: Loss of balance.
Athetosis: Abnormal involuntary movements that are slow, repetitive, and sinuous.
Autonomic nervous system: The part of the body's complex system of nerves that controls the involuntary activity of some of the internal organs, such as breathing or heartbeat.