Download Interference to Neurotransmitter function

Unit 3 Psychology
Area of Study 1: How does the nervous system enable
psychological functioning?
Key knowledge: Dot point 5
“The effects of chronic changes to the functioning of the nervous system due to interference
to neurotransmitter function, illustrated by the role of Dopamine in Parkinson’s disease.”
Interference to Neurotransmitter function
A variety of brain and nervous system diseases are caused by changes in the functioning of
neurotransmitters. These diseases often have a genetic basis, but can also be caused by
environmental factors such as viruses, tumours, stroke and chemicals.
Malfunctioning of neurotransmitters can lead to neurodegenerative diseases, such as
Parkinson’s disease.
Neurodegenerative disease: a disease that gradually and progressively kills nerve cells
(neurons) and results in nervous system dysfunction and permanent loss of ability.
Parkinson’s Disease
Parkinson’s disease: a CNS neurodegenerative disorder characterised by both motor and
non-motor symptoms.
Causes
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The cause of Parkinson’s is still not known and there is no evidence that it has a
genetic basis.
Neurons start to degenerate in the substantia nigra in the midbrain.
The substantia nigra has a role in the smooth and coordinated production of
voluntary movements.
Neurons in the substantia nigra produce the neurotransmitter dopamine. When this
area is damaged, the levels of dopamine are reduced.
Less dopamine means less motor activity, as dopamine is the neurotransmitter
responsible for controlling voluntary motor movements.
The substantia nigra releases dopamine and sends the messages about motor
movements to the basal ganglia and then the motor cortex, in the frontal lobe.
The basal ganglia is located at the base of the forebrain and is involved in motor
function.
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As the neurons die in the substantia nigra there is less dopamine produced.
With lower levels of dopamine, the messages travelling to the motor cortex to
control voluntary movements are slower and fewer. This causes impairments in the
control of voluntary movements and some of the major symptoms of Parkinson’s
disease.
Motor symptoms only appear after substantial neuronal death in the substantia
nigra. Approximately 60% of the neurons need to die before symptoms start
occurring.
Symptoms
Symptoms of Parkinson’s disease develop slowly and the severity increases over a number
of years.
Symptoms include:
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Tremors
Muscular rigidity
Reduced control over voluntary movement (including speech)
Pain and discomfort in arm or leg
Constipation and bladder problems
Speech and swallowing problems (as the disease progresses)
Temperature regulation, digestion and sexual function problems
Cognitive dysfunction also occurs, which can include slowness of thinking and
memory problems. Dementia may occur in the later stages of the disease
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The four main symptoms for diagnosis:
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Tremor or shaking (most common) that usually starts in one hand
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Muscle rigidity, stiffness of the muscles which seem unable to relax
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Bradykinesia (slowness of movement and gradual loss of spontaneous movement)
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Postural instability, balance problems and gait (walking) disturbances
Diagnosis
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Neuroimaging has made advances in early diagnosis of Parkinson’s disease. Both MRI
and PET scans can show changes to the brain in Parkinson’s disease.
PET imaging: PET scans show the dopamine producing areas of the brain. It makes it
possible to assess changes in the activity and function of the brain
PET imaging diagnoses Parkinson’s by injecting a patient with the drug, 18F-DOPA.
This drug is similar to dopamine. It shows the deterioration of the pathways in the
substantia nigra, if a person has Parkinson’s.
If it is not Parkinson’s, but another movement disorder, there won’t be any
deterioration of the substantia nigra
Treatment
• There are two drugs used to treat Parkinson’s disease:
• Levodopa (L-Dopa) can cross the blood-brain barrier and be converted into
dopamine by the brain.
• Dopamine agonists stimulate the dopamine receptors in the brain, mimicking the
effect of dopamine in the brain.
• Both drugs can alleviate symptoms of Parkinson’s, but are not a cure. The disease
continues to progress until the drugs do not work anymore (5-10 years maximum
benefit) or cause side effects such as dyskinesia, which are just as bad as the disease.
• Dyskinesia is abnormal involuntary muscle movements.
• Another treatment offer is Deep Brain Stimulation.
• Deep Brain Stimulation (DBS): a surgical procedure that involves the
implantation of a neurotransmitter into the brain so electrical impulses can be
delivered to specific parts of the brain to activate them
• When the electrical impulses stimulated the neurons that control movement, it
blocked the signals causing the tremors, alleviating some of the symptoms of
Parkinson’s disease.
• DBS is usually used in conjunction with drugs. DBS does not halt the progression of
the disease.
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