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Glossary 487fashion. Binding transmits the extracellular signal and triggers specific physiologicalevents within the postsynaptic cell.Reversal potential The membrane voltage at which there is no net flow of ionsfrom one side of the membrane to the other.Serotonin (5 hydroxytryptamine) A monoamine neurotransmitter that is apowerful vasoconstrictor and is found in the brain, blood serum, and gastric mucousmembrane of mammals. In the CNS, serotonin is thought to play a majorrole in regulation of mood, sleep, emesis, sexuality, and appetite, and is implicatedin the pathophysiology of many disorders, such as depression, migraines,bipolar disorder, and anxiety.5 HT (serotonin) receptor A receptor of serotonin, as well as a broad range ofpharmaceutical and hallucinogenic drugs such as antidepressants, anxiolytics, andantoemetics. There are many subtypes (5 HT 1A, 5 HT 1B, 5 HT 1D, 5 HT 2A , 5 HT 2B,5 HT 2C , 5 HT 3, 5 HT 4, 5 HT 5, 5 HT 6, 5 HT 7 ) of this receptor that all have differentactions, agonists, and antagonists.Serotonin transporter A monoamine transporter protein that regulates theserotonin concentration in the synapse by recycling serotonin back into the neuron.SSRIs (selective serotonin reuptake inhibitors) reduce binding of serotoninto the transporter, increasing its time and therefore effect in the synaptic cleft, andare used to treat depression and OCD.Signal transduction Any process, taking a millisecond or as long as a few seconds,by which a cell converts one kind of signal or stimulus into another, ofteninvolving a sequence of biochemical reactions inside the cell that are carried outby enzymes and linked through second messengers.Spatial resolution The ability to sharply and clearly define the extent or shapeof features within an image, describing how close two features can be and still beresolved as unique.Steroid hormones Any of numerous hormones (such as glucocorticoids, mineralocorticoids,androgens, estrogens, and progestogens) having the characteristicring structure of steroids and formed in the body from cholesterol.Striatum A subcortical brain structure, consisting of the caudate nucleus andthe putamen, that plays important roles in planning and modulating movementpathways and other cognitive processes involving executive function. See FigureB2.