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Transcript
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 • • • • • • • 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. 1 • • • 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: • • • • • • • • 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 2 The four main symptoms for diagnosis: • Tremor or shaking (most common) that usually starts in one hand • Muscle rigidity, stiffness of the muscles which seem unable to relax • Bradykinesia (slowness of movement and gradual loss of spontaneous movement) • Postural instability, balance problems and gait (walking) disturbances Diagnosis • • • • 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. *Videos **Student Activity Manual – 1.9 3