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The human body has been conditioned to recognize patterns of restfulness and sleep times over thousands of years. The circadian rhythm encompasses physical, mental, and behavioral changes taking place over a daily cycle, which is a result of exposure to light and darkness in our environment. This rhythm is responsible for dictating the drive to sleep not only in humans and animals, but it also plays a role in the functionality of plants and microscopic organisms.
Daylight is among the most powerful influencers compelling us to sleep. When our eyes pick up light rays, they are converted into electrical waves that pass to the optic nerve. Thereafter, the optic nerve relays the message to the body’s “Master Clock,” or the Superchiasmatic Nucleus (SCN), which acts as a master circadian pacemaker controlling the timing of sleep-wake cycles. The SCN comprises thousands of neurons which work in tandem with one another to relay messages across the entire body. As the day winds down and the sun begins to set, the optic nerve then relays this new message to the SCN, which then releases serotonin. Our bodies convert serotonin into melatonin, allowing us to relax and ease into the first stage of sleep.
In the Textbook of Age Management Medicine: Volume 1, authors Jeffrey P. Leake, MD and Todd D. Greenberg, MD note that sleep is classified into three separate phases: wakefulness, non-rapid eye movement (REM) sleep, and REM sleep. Joshua D’Alessandro, New York City-based Nutrition and Exercise Counselor, explains that these categories are further classified into the five stages of the sleep timeline:
In individuals who cannot recall the last night of sleep lasting seven to nine hours, serious changes need to be made to rearrange schedules for prioritizing slumber.
This guide was produced with contributions from the following key resources:
The Cenegenics Education and Research Foundation
The Textbook of Age Management Medicine Volume 1: Mastering Healthy Aging Nutrition, Exercise and Hormone Replacement Therapy
Nutrition and Exercise Counselor | Cenegenics New York City
Jeffrey Park Leake, M.D., CPT
Dr. Jeffrey Park Leake is a Partner and Director of Education at Cenegenics Elite Health specializing in age management and wellness. Having trained hundreds of physicians worldwide, Dr. Leake is also the Director of Education for the Clinical Strategies for Healthy Aging course at AMM Education Foundation.
Todd David Greenberg, M.D., CSCS
Dr. Todd Greenberg is a practicing physician with a broad range of expertise, including wellness, exercise, sports injuries, and MRI of sports injuries. He is a Radiology Clinical Associate Professor at the University of Washington.
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We hope the information above assisted you in your research process.
 “Circadian Rhythms.” National Institute of General Medical Sciences. Aug. 2017. Retrieved from URL: https://www.nigms.nih.gov/Education/Pages/Factsheet_CircadianRhythms.aspx
 Moore, R.Y. “Suprachiasmatic nucleus in sleep-wake regulation.” Sleep Med. Dec. 2007. Retrieved from URL: https://www.ncbi.nlm.nih.gov/pubmed/18032104.
 “Understanding Sleep Cycles: What Happens While You Sleep.” National Sleep Foundation. Retrieved from URL: https://sleep.org/articles/what-happens-during-sleep/
 “Sleep and Sleep Disorder Statistics.” See above.
 “What is REM sleep?” Eunice Kennedy Shriver National Institute of Child Health and Human Development. 01 Dec. 2016. Retrieved from URL: https://www.nichd.nih.gov/health/topics/sleep/conditioninfo/rem-sleep.
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