The circadian rhythm keeps an organism's body in sync with night and day to keep the body's systems in order. The word circadian comes from the Latin word circa diem, meaning about one day (JCI). It was first identified in 1729 by Jean Jacques d'Ortuous de Marian, a French astronomer, geophysicist and, most importantly, chronobiologist. Chronobiology is a type of science that examines natural phenomena and rhythms such as the circadian rhythm (Serendip). He was born on November 26, 1678 and died on February 20, 1771. Being interested in chronobiology, the study of the effects of day and night on living organisms, he demonstrated the existence of the circadian rhythm in plants. To reach this conclusion he observed that a type of plant, Mimosa pudica, still opened its leaves during the day and closed them at night if placed in a completely dark environment. With this shocking discovery, he concluded that “circadian rhythms persist without environmental cues” (The Guardian). “A circadian rhythm is an approximately 24-hour cycle in the physiological processes of living things, including plants, animals, fungi and cyanobacteria” (The Science Daily). The biological clock that the circadian rhythm relies on to function is regulated by the suprachiasmatic nucleus (SCN), also called the pacemaker in the hypothalamus portion of the brain. The hypothalamus controls a variety of functions in the body, from the nervous system to the endocrine system. It is located in the central base of the brain and encloses the ventral part of the third ventricle. Located within the hypothalamus, the suprachiasmatic nucleus (SCN) connects to the optic nerve that receives light and is made up of a cluster of nerve cells, approximately 20,000 neu...... middle of paper ..... .ine, nd Web. May 27, 2014. “Result Filters.” National Center for Biotechnology Information. U.S. National Library of Medicine, n.d. Web. May 27, 2014. “Result Filters.” National Center for Biotechnology Information. U.S. National Library of Medicine, n.d. Web. May 27, 2014. “Result Filters.” National Center for Biotechnology Information. U.S. National Library of Medicine, n.d. Web. May 27, 2014. “Sleep and the Biological Clock.” Biological Clock and Sleep 2. Np, nd Web. May 27, 2014. “Let's talk about the circadian rhythm.” Studio Serendip. Np, nd Web. May 27 2014. .