Melatonin is a hormone which is an indolamine derivative of serotonin secreted from the pineal gland into the blood and CSF in response to darkness. In the presence of light it's secretion is inhibited. Melatonin also has effects on the production of luteinizing hormone (LH) and follicle stimulating hormone (FSH) from the anterior pituitary gland. In long day breeders the increasing daylight hours cause a decrease in melatonin. In response, production of LH and FSH is uninhibited and so libido rises. In short day breeders an increase in melatonin causes a rise in production of LH and FSH and so leads to an increase in libido. The purpose of melatonin in many mammals appears to be the control of physiologic rhythms by altering the timing of circadian rhythm data relayed from the suprachiasmatic nucleus in the hypothalamus. Melatonin may inhibit dopamine, reduce free radical production and central nervous system excitability as well as augmenting GABA.

Psychology is designed to meet scope and sequence requirements for the single-semester introduction to psychology course. The book offers a comprehensive treatment of core concepts, grounded in both classic studies and current and emerging research. The text also includes coverage of the DSM-5 in examinations of psychological disorders. Psychology incorporates discussions that reflect the diversity within the discipline, as well as the diversity of cultures and communities across the globe.Senior Contributing AuthorsRose M. Spielman, Formerly of Quinnipiac UniversityContributing AuthorsKathryn Dumper, Bainbridge State CollegeWilliam Jenkins, Mercer UniversityArlene Lacombe, Saint Joseph's UniversityMarilyn Lovett, Livingstone CollegeMarion Perlmutter, University of Michigan

By the end of this section, you will be able to:

Understand what is meant by consciousness
Explain how circadian rhythms are involved in regulating the sleep-wake cycle, and how circadian cycles can be disrupted
Discuss the concept of sleep debt