Answer to Question 1
C
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Degeneration of dopamine-releasing neurons in the substantia nigra leads to Parkinson's disease. When dopamine is decreased in the area of the corpus striatum, a chemical imbalance allows the cholinergic or excitatory cells to dominate. This affects the functioning of the basal ganglia and cortical and cerebellar components of the extrapyramidal motor system. This system provides coordination for unconscious muscle movements, including those that control position, posture, and movement. The result of the imbalance produces the signs and symptoms of Parkinson's disease. The corpus striatum in the brain is connected to the substantia nigra by a series of neurons that use the inhibitory neurotransmitter GABA. Higher neurons from the cerebral cortex secrete acetylcholine in the area of the corpus striatum as an excitatory neurotransmitter to coordinate movements of the body. Serotonin is not involved in these functions.
Answer to Question 2
A
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The pressure in the cardiovascular system is determined by three elements: heart rate, stroke volume, and peripheral resistance. The small arterioles are thought to be the most important factors in determining peripheral resistance. Because they have the smallest diameter, they are able to almost stop blood flow into capillary beds when they constrict, building up tremendous pressure in the arteries behind them as they prevent the blood from flowing through.
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