Chapter 7: Movement Disorders Flashcards
Parkinson’s disease 252
The main symptoms of Parkinson’s disease (also known as are rigidity, muscle tremors, slow movements,
and difficulty initiating physical and mental activity. It becomes more common as people age, striking 1 percent to 2 percent of people over age 65. Early symptoms usually include loss of olfaction and psychological depression. Many but not all Parkinson’s patients have cognitive deficits, which may include problems with attention, language, or memory. The immediate cause of Parkinson’s disease is the gradual
loss of neurons in the substantia nigra and therefore a loss of dopamine-releasing axons to the striatum (part of the basal ganglia). The result is less vigorous voluntary movements. People with Parkinson’s disease are still capable of movement. However, their spontaneous movements are slow and weak. Genes has no risky contribution.
L-dopa 253
Because Parkinson’s disease results from a dopamine
deficiency, a logical goal is to restore the missing dopamine. A dopamine pill would be ineffective because dopamine does not cross the blood–brain.barrier.
MPTP & MPP+ 253
Several young adults developed symptoms of Parkinson’s disease after using a drug similar to heroin.The substance responsible for the symptoms was MPTP, a chemical that the body converts to MPP+, which accumulates in, and then destroys, neurons that release dopamine, partly by impairing the transport of mitochondria from the cell body to the synapse. Postsynaptic neurons react to the loss of input by increasing their number of dopamine receptors. L-dopa is still the most common treatment for Parkinson’s disease. it does not replace other transmitters
that are also depleted. It does not slow the continuing loss of neurons. And it produces unpleasant side effects such as nausea, restlessness, sleep
problems, low blood pressure, repetitive movements, and sometimes hallucinations and delusions. The most common choices are drugs that directly stimulate dopamine receptors and drugs that block the metabolic breakdown of dopamine. To varying degrees, these drugs reduce the symptoms, but none of them
halt the underlying disease. Despite many efforts, drugs toprevent the further loss of neurons have been unsuccessful so far.
Huntington’s disease 254
Ιτ is a severe neurological disorder that strikes about 1 person in 10,000. Motor symptoms usually begin with arm jerks and facial twitches. Then tremors. Gradually, the tremors interfere more and more with walking, speech, and other voluntary movements. People lose the ability to learn or improve motor skills. Extensive brain damage, basal ganglia & the cerebral cortex. It increase produces the involuntary jerky movements. People with Huntington’s disease also suffer psychological disorders: depression, sleeplessness, memory impairment, anxiety, hallucinations and delusions, poor judgment, alcoholism, drug abuse, and sexual disorders ranging from complete unresponsiveness to indiscriminate promiscuity. Occasionally, individuals in the early stages of Huntington’s disease are misdiagnosed as having schizophrenia. Huntington’s disease can occur at any age, but most often between the ages of 30 and 50. The critical area of the gene includes a sequence of bases C-A-G (cytosine, adenine, guanine), which is repeated 11 to 24 times in most people. That repetition produces a string of 11 to 24 glutamines in the resulting protein. People with up to 35 C-A-G repetitions are considered safe from Huntington’s disease. Those with 36 to 38 might or might not get it, but probably not before old age. People with 39 or more repetitions are likely to get the disease, unless they die of other causes earlier. The more C-A-G repetitions someone has, the earlier the probable onset of the disease.
stem cells 254
A related approach is to take stem cells—immature cells that are capable of differentiating into other cell types—guide their development so that they produce large quantities of L-dopa, and then transplant them into the brain.
huntingtin 256
Identification of the gene for Huntington’s disease led
to the discovery of the protein that it codes, which has been designated huntingtin. Huntingtin occurs throughout the human body, although its mutant form produces no known harm outside the brain. Within the brain, it occurs inside neurons, not on their membranes. The mutant form impairs neurons in several ways. In the early stages of the disease, it increases eurotransmitter release, sometimes causing overstimulation of the target cells. Later, the protein forms clusters that impair the neuron’s mitochondria. It also impairs the transport of chemicals down the axon.
