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A circadian rhythm, or circadian cycle, is a natural oscillation that repeats roughly every 24 hours. Circadian rhythms can refer to any process that originates within an organism and responds to the environment. Circadian rhythms are regulated by a circadian clock whose primary function is to rhythmically co-ordinate biological processes so they occur at the correct time to maximise the fitness of an individual. Circadian rhythms have been widely observed in animals, plants, fungi and cyanobacteria and there is evidence that they evolved independently in each of these kingdoms of life.
Chronobiology is a field of biology that examines timing processes, including periodic (cyclic) phenomena in living organisms, such as their adaptation to solar- and lunar-related rhythms. These cycles are known as biological rhythms. Chronobiology comes from the ancient Greek χρόνος, and biology, which pertains to the study, or science, of life. The related terms chronomics and chronome have been used in some cases to describe either the molecular mechanisms involved in chronobiological phenomena or the more quantitative aspects of chronobiology, particularly where comparison of cycles between organisms is required.
Delayed sleep phase disorder (DSPD), more often known as delayed sleep phase syndrome and also as delayed sleep–wake phase disorder, is the delaying of a person's circadian rhythm compared to those of societal norms. The disorder affects the timing of biological rhythms including sleep, peak period of alertness, core body temperature, and hormonal cycles.
Advanced Sleep Phase Disorder (ASPD), also known as the advanced sleep-phase type (ASPT) of circadian rhythm sleep disorder, is a condition that is characterized by a recurrent pattern of early evening sleepiness and very early morning awakening. This sleep phase advancement can interfere with daily social and work schedules, and results in shortened sleep duration and excessive daytime sleepiness. The timing of sleep and melatonin levels are regulated by the body's central circadian clock, which is located in the suprachiasmatic nucleus in the hypothalamus.
A zeitgeber is any external or environmental cue that entrains or synchronizes an organism's biological rhythms, usually naturally occurring and serving to entrain to the Earth's 24-hour light/dark and 12-month cycles.
A night owl, evening person or simply owl, is a person who tends or prefers to be active late at night and into the early morning, and to sleep and wake up later than is considered normal; night owls often work or engage in recreational activities late into the night, and sleep until relatively late in the day.
Circadian rhythm sleep disorders (CRSD), also known as circadian rhythm sleep-wake disorders (CRSWD), are a family of sleep disorders which affect the timing of sleep. CRSDs arise from a persistent pattern of sleep/wake disturbances that can be caused either by dysfunction in one's biological clock system, or by misalignment between one's endogenous oscillator and externally imposed cues. As a result of this mismatch, those affected by circadian rhythm sleep disorders have a tendency to fall asleep at unconventional time points in the day. These occurrences often lead to recurring instances of disturbed rest, where individuals affected by the disorder are unable to go to sleep and awaken at "normal" times for work, school, and other social obligations. Delayed sleep phase disorder, advanced sleep phase disorder, non-24-hour sleep–wake disorder and irregular sleep–wake rhythm disorder represents the four main types of CRSD.
Sleep medicine is a medical specialty or subspecialty devoted to the diagnosis and therapy of sleep disturbances and disorders. From the middle of the 20th century, research has provided increasing knowledge of, and answered many questions about, sleep–wake functioning. The rapidly evolving field has become a recognized medical subspecialty in some countries. Dental sleep medicine also qualifies for board certification in some countries. Properly organized, minimum 12-month, postgraduate training programs are still being defined in the United States. In some countries, the sleep researchers and the physicians who treat patients may be the same people.
In the study of chronobiology, entrainment occurs when rhythmic physiological or behavioral events match their period to that of an environmental oscillation. It is ultimately the interaction between circadian rhythms and the environment. A central example is the entrainment of circadian rhythms to the daily light–dark cycle, which ultimately is determined by the Earth's rotation. Exposure to certain environmental stimuli will cue a phase shift, and abrupt change in the timing of the rhythm. Entrainment helps organisms maintain an adaptive phase relationship with the environment as well as prevent drifting of a free running rhythm. This stable phase relationship achieved is thought to be the main function of entrainment.
A chronotype is the behavioral manifestation of underlying circadian rhythm's myriad of physical processes. A person's chronotype is the propensity for the individual to sleep at a particular time during a 24-hour period. Eveningness and morningness are the two extremes with most individuals having some flexibility in the timing of their sleep period. However, across development there are changes in the propensity of the sleep period with pre-pubescent children preferring an advanced sleep period, adolescents preferring a delayed sleep period and many elderly preferring an advanced sleep period.
Light effects on circadian rhythm are the effects that light has on circadian rhythm.
A sleep study is a test that records the activity of the body during sleep. There are five main types of sleep studies that use different methods to test for different sleep characteristics and disorders. These include simple sleep studies, polysomnography, multiple sleep latency tests (MSLTs), maintenance of wakefulness tests (MWTs), and home sleep tests (HSTs). In medicine, sleep studies have been useful in identifying and ruling out various sleep disorders. Sleep studies have also been valuable to psychology, in which they have provided insight into brain activity and the other physiological factors of both sleep disorders and normal sleep. This has allowed further research to be done on the relationship between sleep and behavioral and psychological factors.
Jürgen Walther Ludwig Aschoff was a German physician, biologist and behavioral physiologist. Together with Erwin Bünning and Colin Pittendrigh, he is considered to be a co-founder of the field of chronobiology.
A lark, early bird, morning person, or an A-person, is a person who usually gets up early in the morning and goes to bed early in the evening. The term relates to the birds known as larks, which are known to sing before dawn. Human "larks" may sleep from around 10 p.m. to 6 a.m., and tend to feel most energetic just after they get up in the morning. They are thus well-suited for working the day shift.
The morningness–eveningness questionnaire (MEQ) is a self-assessment questionnaire developed by researchers James A. Horne and Olov Östberg in 1976. Its main purpose is to measure whether a person's circadian rhythm produces peak alertness in the morning, in the evening, or in between. The original study showed that the subjective time of peak alertness correlates with the time of peak body temperature; morning types have an earlier temperature peak than evening types, with intermediate types having temperature peaks between the morning and evening chronotype groups. The MEQ is widely used in psychological and medical research and has been professionally cited more than 4,000 times.
Till Roenneberg is a professor of chronobiology at the Institute of Medical Psychology at Ludwig-Maximilian University (LMU) in Munich, Germany. Roenneberg, in collaboration with Martha Merrow, explores the impact of light on human circadian rhythms, focusing on aspects such as chronotypes and social jet lag in relation to health benefits.
Amita Sehgal is a molecular biologist and chronobiologist in the Department of Neuroscience at the Perelman School of Medicine at the University of Pennsylvania. Sehgal was involved in the discovery of Drosophila TIM and many other important components of the Drosophila clock mechanism. Sehgal also played a pivotal role in the development of Drosophila as a model for the study of sleep. Her research continues to be focused on understanding the genetic basis of sleep and also how circadian systems relate to other aspects of physiology.
Martha Merrow is an American chronobiologist. She currently chairs the Institute of Medical Psychology at the Ludwig Maximilian University of Munich. Her career focuses primarily on investigating the molecular and genetic mechanisms of the circadian clock. Since joining the Ludwig Maximilian University in 1996, Merrow has investigated molecular and genetic mechanisms of the circadian clock as well as daily human behavior and medical psychology.
The bunker experiment was a scientific experiment that began in 1966 to test whether humans, like other species, have an intrinsic circadian clock. It was started by Jürgen Aschoff and Rütger Wever of the Max Planck Institute for Behavioral Physiology and later taken over by Jürgen Zulley. Participants lived in a bunker for multiple weeks while scientists measured their daily rhythms in many variables. The main conclusion of the experiment was that humans have an intrinsic clock with a period greater than 24 hours. The experiment also established many features of this clock and paved the way for future circadian studies.
Familial sleep traits are heritable variations in sleep patterns, resulting in abnormal sleep-wake times and/or abnormal sleep length.
References
- ↑ "MCTQ - Main Page". WeP Project. Retrieved 2018-05-03.
- ↑ The search for circadian clock components in humans: new perspectives for association studies. Allebrandt KV, Roenneberg T. Braz J Med Biol Res. 2008 Aug;41(8):716-21.