7.3.2 Parkinson’s Disease
Parkinson’s disease（PD）is a neurodegenerative disease caused by a loss of nerve cells（neurons）in the black substance（substantia nigra）of the brain（Fig.7-6）.These cells produce a neurotransmitter called dopamine that helps to regulate movement.PD occurs when，for unknown reasons，certain neurons in the midbrain fail to secrete the neurotransmitter dopamine.
Fig.7-6 Parkinson’s Disease
The most recognizable early symptoms are motor-related，e.g.tremor，slowness of movement（bradykinesia），and muscle stiffness（rigidity）that can make it difficult to move around and make facial expressions，and can result in painful muscle cramps（dystonia）.Non-motor symptoms，including autonomic dysfunction（dysautonomia），neuropsychiatric problems（mood，cognition，behavior or thought alterations），and sensory（especially altered sense of smell）and sleep difficulties（insomnia），are usually associated with later stages，but may present at the time of diagnosis.
No cure for Parkinson’s disease is known.Levodopa is the most potent drug for controlling PD symptoms，particularly those related to bradykinesia.Surgery is being used in people with advanced PD for whom drug therapy is no longer sufficient.Surgery for PD can be divided into two main groups—lesional and deep brain stimulation（DBS）.DBSinvolves the implantation of a medical device called a neurostimulator，which sends electrical impulses to specific parts of the brain.Other less common surgical therapies involve intentional formation of lesions to suppress overactivity of specific subcortical areas.For example，pallidotomy involves surgical destruction of the globus pallidus to control dyskinesia.Regular physical exercise with or without physical therapy can be beneficial to maintain and improve mobility，flexibility，strength，gait speed，and quality of life in people with PD.
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Task 4 Decide whether the following statements are true（T）or false（F）according to the text.
1.PD results from the loss of neurons in substantia nigra.（ ）
2.Neurotransmitter as a chemical messenger helps to regulate body growth.（ ）
3.Non-motor symptoms are the most early identifiable manifestations of Parkinson’s disease.（ ）
4.Levodopa is the most effective drug for controlling those symptoms related to abnormal slowness of physical movement.（ ）
5.A neurostimulator is a chemical substance that allow neurons to communicate with each other throughout the body.（ ）