Answers and Explanations

1. M. The highest concentration of serotonin in the CNS is found in the pineal body (epiphysis cerebri). Pinealocytes convert 5-HT to melatonin. The vast majority of serotonin in the body is found in the gut. 2. O. Substance P is the neurotransmitter of pain fibers and is found in pseudounipolar ganglion cells and in the substantia gelatinosa of the spinal cord. Substance P is also found in the caudal part of the spinal trigeminal tract. 3. K. Nitric oxide is responsible for the smooth muscle relaxation of the corpus cavernosum and thus penile erection. 4. L. The highest concentration of norepinephrinergic neurons is found in the locus ceruleus. 5. I. Glutamate is the neurotransmitter of the corticostriatal pathway. 6. M. Serotonin is produced by neurons of the raphe nuclei of the brainstem. 7. B. Aspartate is the neurotransmitter of the climbing fibers of the cerebellum. 8. M. Low levels of 5-HT are associated with severe depression and insomnia. 9. A. ACh is found in highest concentration in the basal nucleus of Meynert, between the anterior perforated substance and the globus pallidus, a forebrain nucleus. 10. E. Endorphin is produced almost exclusively in the hypothalamus (arcuate nucleus). 11. A. In myasthenia gravis, there is a reduced ACh receptor concentration in the motor end plate owing to an autoimmune reaction directed against the receptor proteins. 12. J. Glycine is the major inhibitory neurotransmitter of the spinal cord; glycine is used by Renshaw cells, inhibitory interneurons driven by axon collaterals of lower motor neurons. 13. H. Striatal levels of GABA are greatly reduced in Huntington disease. This attrition of GABA-ergic neurons in the head of the caudate nucleus results in hydrocephalus ex vacuo. 14. H. GABA is the neurotransmitter of the Purkinje cells. 15. I. Glutamate is the neurotransmitter of the cerebellar granule cells. 16. D. Dopamine is found in high concentration in the pars compacta of the substantia nigra and in the ventral tegmental area of the mesencephalon. 17. D. Dopamine is the neurotransmitter of the mesolimbic pathway. This pathway is linked to be havior and schizophrenia. 18. D. Dopamine inhibits the release of prolactin from the adenohypophysis. Dopaminergic neurons are found in the arcuate nucleus of the hypothalamus. 19. H. GABA, the most common inhibitory neurotransmitter of the brain, is the main neurotransmit ter of the pallidothalamic and nigrothalamic tracts. 20. E. Parkinson disease results from degeneration of dopaminergic neurons found in the pars com pacta of the substantia nigra. Although Parkinson disease is typically diagnosed based on neuro logic symptoms, a positron emission tomography scan with radioactive labeling can sometimes be used as a diagnostic tool. 21. D. Myasthenia gravis is an autoimmune syndrome whose symptoms usually include the pres ence of antibodies to the nicotinic ACh receptor. Other symptoms include muscle paresis, diplo pia, ptosis, jaw fatigue, and weak proximal limbs. 22. A. Alzheimer disease is characterized histologically by the presence of neurofibrillary tangles, senile (neuritic) plaques, granulovacuolar degeneration, and Hirano bodies. This disease results from the degeneration of cortical neurons and cholinergic neurons found in the basal nucleus of Meynert. It is also associated with a 60% to 90% loss of choline acetyltransferase in the cerebral cortex.

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