Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Pages: 83. Chapters: Actigraphy, Advanced sleep phase disorder, Bacterial circadian rhythms, Chronobiology, Chronobiotic, Chronotherapy, Chronotype, Circadian clock, Circadian rhythm sleep disorder, Circasemidian rhythm, Circaseptan, Dark therapy, David F. Dinges, Dawn simulation, Delayed sleep phase disorder, Diurnality, Entrainment (chronobiology), Franz Halberg, Free-running sleep, Giant retinal ganglion cells, Irregular sleep-wake rhythm, Jet lag, Jurgen Aschoff, Lark (person), Light effects on circadian rhythm, Light in school buildings, Light therapy, Melanopsin, Melatonin, N-Acetylserotonin, Nathaniel Kleitman, Night owl (person), Nocturnality, Non-24-hour sleep-wake disorder, Phase response curve, Photoperiodism, Photoreceptor protein, Photosensitive ganglion cell, Pineal gland, Polyphasic sleep, Retinohypothalamic tract, Roberto Refinetti, Russell G. Foster, Rutger Wever, Sara Mednick, Seasonal affective disorder, Segmented sleep, Shift work, Shift work sleep disorder, Sleep diary, Sleep inertia, Sleep phase chronotherapy, Sundowning, Suprachiasmatic nucleus, Ultradian, Zeitgeber. Excerpt: Melatonin, is also known chemically as N-acetyl-5-methoxytryptamine, is a naturally occurring compound found in animals, plants, and microbes. In animals, circulating levels of the hormone melatonin vary in a daily cycle, thereby allowing the entrainment of the circadian rhythms of several biological functions. Many biological effects of melatonin are produced through activation of melatonin receptors, while others are due to its role as a pervasive and powerful antioxidant, with a particular role in the protection of nuclear and mitochondrial DNA. Products containing melatonin have been available over-the-counter in the United States since the mid-1990s. In many other countries, the sale of this neurohormone is not permitted or requires...