Cocaine lowers the levels of a chemical messenger in the brain called enkephalin. Researchers have found the number of enkephalin receptors to be higher in cocaine addicts than nonaddicted people. This is an example of
A. saturation.
B. up-regulation.
C. antagonism.
D. affinity.
E. down-regulation.
B
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The interaction between Ca2+ and calmodulin in smooth muscle cells has been described as a second messenger system. Develop an argument to support this position, using another second messenger system you have studied for comparison.
What will be an ideal response?
Which cell has a very small, darkly staining nucleus?
a. Erythrocyte b. Normoblast c. Polychromatophilic erythroblast d. Proerythroblast e. Reticulocyte
Variations in eye color are determined by the number of pigmented cells in the:
a. Ciliary epithelium b. Corneal epithelium c. Corneal stroma d. Iris epithelium e. Iris stroma
Which type of muscle tissue causes contraction of the heart?
A. skeletal muscle B. smooth muscle C. cardiac muscle