Sleep wake cycle

Category A - full version without watermark 720x576 (check terms and conditions at The embed version with watermark is free of charge. - Descriptionh: Light exposure to the retina is first relayed to the suprachiasmatic nucleus of the hypothalamus, an area of the brain well known to coordinate biological clock signals. Fibers from the hypothalamus descend to the spinal cord and ultimately project to the superior cervical ganglia, from which post-ganglionic neurons ascend back to the pineal gland. Thus, the pineal is similar to the adrenal medulla in the sense that it transduces signals from the sympathetic nervous system into a hormonal signal. The precursor to melatonin is serotonin, a neurotransmitter that itself is derived from the amino acid tryptophan. Within the pineal gland, serotonin is acetylated and then methylated to yield melatonin. Melatonin has important effects in integrating photoperiod and affecting circadian rhythms. Consequently, it has been reported to have significant effects on reproduction, sleep-wake cycles and other phenomena showing circadian rhythm.