Which of the following is an example of an extended definition? Here are some tips to use your knowledge of circadian rhythms to help you get a good night's sleep. Go to sleep at the same time every night to help set a consistent sleep schedule. Also, use natural light to your advantage: get light first thing in the morning and then dim the lights in the evening when it's time to go to bed. Circadian rhythms (noun) are defined by the National institute of General Medical Science as the "physical, mental, and behavioral changes that follow a roughly 24-hour cycle, responding primarily to light and darkness in an organism's environment. They are found in most living things, including animals, plants and many tiny microbes." Circadian rhythms, often referred to as the "body clock," are the physical, mental, and behavioral changes that you experience during a 24-hour period. One main reason you can have disturbances with your sleep has to do with circadian rhythms - also called your "body clock." Circadian rhythms are the changes that take place in your body and behavior during each period of approximately 24 hours. Changes in your body temperature and appetite level are examples of circadian rhythms. Circadian rhythms help regulate melatonin, a hormone that helps you feel sleepy.