The Physiology of Normal Sleep

pISSN 1738-429X eISSN 2234-4446 Sleep is a highly organized and complicated state that is fundamental to life. We have an absolute need to sleep during about one-third of our lives. There are two types of sleep, non-rapid eye movement (NREM) and rapid eye movement (REM) sleep. NREM sleep is di-vided into stages 1, 2, and 3 which is representing a degree of relative depth in sleep. Each sleep stage shows unique features including some variations in electroencephalographic waves, eye movements, and muscle tone. Although sleep pattern changes are associated with aging, how sleep physiology and sleep patterns change over an individual’s life span is not well-defined. Circadian rhythms, which are the daily rhythms in physiology and be-havior, regulate the sleep-wake cycle. Comprehensive understanding of normal sleep physiology should be very important to better understand not only the effects of sleep re-lated diseases but also the impacts of pathological sleep on various diseases of other sys-temic organs. This review aims to enhance knowledge focused on normal sleep physiolog