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Actogram — a type of graph or chart commonly used in circadian research to plot activity (present or absent) against time |
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Ambient temperature — external or environmental temperature |
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Biological clock — a term introduced in the 1950s to refer to the internal or innate timing or time measuring mechanisms within organisms |
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Circadian — a term introduced in the 1950s, meaning of approximately 24-hour duration, which comes from the Latin circa (about) and dies (day) |
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Circannual rhythm — the rhythm produced when the internal biological clock also operates on an annual basis |
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clk — the genetic abbreviation for the non-mammalian gene that is analogous to the mammalian Clock gene |
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cyc — the genetic abbreviation for the gene named cycle |
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Endogenous — inside or within. For example, transcription is an endogenous activity in cells. |
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Entrainment — synchronization of a rhythm (such as a circadian rhythm) to a repetitive signal or environmental cue (such as the rising or setting of the sun) |
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Free-running — in the context of biological clocks, refers to a biological system that functions on its own, in the absence of external cues |
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Genomics — the field of science that focuses on the structure and function of an organism's entire genetic material found in its chromosomes and other cell locations |
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Hypothalamus — section of the mammalian brain that serves to regulate body temperature and various other physiological, behavioral, and biochemical systems |
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Local Clock — individual tissues of the body each having their own endogenous clock. The Master Clock appears to synchronize these local clocks. But in certain cases, the synchrony gets disrupted. This is thought to be the basis of physical effects that result from jet lag. In other words, jet lag interferes with the synchronization between the master and local clocks. Local clocks take varying amounts of time to re-synchronize depending on which tissue(s) are involved. Thus, symptoms may persist until synchrony is adequately re-established. |
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Master Clock — the cells that make up the suprachiasmatic nuclei (SCN) of the brain. This controls the overall circadian rhythm of the organism. |
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Melatonin — hormone secreted by the pineal gland that is involved in the sleep/wakefulness cycle |
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Metabolism — the chemical processes within cells that use nutrients such as oxygen and amino acids to produce energy. Energy is required to fuel the activities essential to life. Metabolism results in the production both of energy and waste materials such as CO2 and water. |
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Molecular feedback loop — the process by which a product stimulates or inhibits its own production |
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Narcolepsy — a condition characterized by extreme daytime sleepiness |
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Negative feedback loop — when used in the context of circadian clocks, refers to the process by which a gene product progressively inhibits transcription of a gene |
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Oscillating system — a system in which a behavior or function over some range repeats itself multiple times or over many periods |
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Oscillation — a repetitive movement or change that alternates between two states or extremes, each of which represents a minimum or a maximum value |
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per — the genetic abbreviation for the gene named period, which was the first clock gene to be discovered |
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Period — the length of time taken to complete a complete cycle of a rhythm |
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Pineal gland — pea-sized brain structure, which secretes melatonin and other hormones in mammals |
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Positive feedback loop — when used in the context of circadian clocks, refers to the process by which a gene product progressively stimulates transcription of a gene |
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Suprachiasmatic Nucleus (SCN) — bilateral structure in the brain's hypothalamus that receives signals about the external environment from the nervous system and uses that information to send hormonal messages |
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Temperature compensation — the capacity of biological clocks to be unaffected by temperature, in contrast to most biological reactions, which double with each 10-degree-Centigrade rise in temperature |
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tim — the genetic abbreviation for the gene named timeless |
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Transcription — the process by which a gene is copied into messenger RNA |
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Translation — the process by which messenger RNA (mRNA) specifies the sequence of a protein |
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Zeitgeber — a German word (literally meaning time-giver) that refers to environmental signals — such as light, temperature, food availability, sound, or social factors — that provide time cues |