The circadian rhythm is a name given to the "internal body clock" that regulates the (roughly) 24 hour cycle of Biology studies the variety of life , tree fern, gazelle, Goliath beetle Biology is the science of life (from the Greek words Life There are many universal units and common processes that are fundamental to the known forms of life. For example all forms of life consist of cells, which in... biological processes in animals and plants. (The term circadian comes from the Latin was the language originally spoken in the region around Rome called Latium. It gained great importance as the formal language of the Roman Empire. All Romance languages are descended from Latin, and many words based on Latin are found in other modern languages such as English. It is said... Latin circa, meaning "around" and dies, "day", meaning literally, "around a day").

Humans have been aware of these cycles since pre-history, as an understanding of these rhythms was essential to early hunters. The formal study of this daily rhythm and other biological rhythms (such as seasonal ones) is called Chronobiology is a field of biology that examines time-related phenomena in living organisms. These cycles are important in many essential biological processes that occur in a scheduled fashion, such as eating, sleeping, mating, hibernating, migration, and cellular regeneration. The most important rhythm in chronobiology is the circadian rhythm, which... chronobiology.

Circadian rhythms are important in determining the Sleeping girl Sleep is the fundamental anabolic process common to all life forms, plant and animal. In animals the anabolic state - sleep - is characterized by an absolute minimal degree of consciousness and decreased responsiveness to the surrounding world. Sleep occurs cyclically, roughly once every 24 hours even though the average... sleeping and feeding patterns of all animals, including humans. There are clear patterns of Electroencephalography is the neurophysiologic exploration of the electrical activity of the brain by the application of electrodes to the scalp. The resulting traces are known as an electroencephalogram (EEG) and represent so-called brain waves. This device is used to assess brain damage, epilepsy and other problems. EEG can also... brain wave activity, A hormone (from Greek or releasing-hormones) Plasma concentrations of ions or nutrients, as well as binding globulins Neurons and mental activity Environmental changes, e.g. of light or temperature Pharmacology A large number of hormones is used as medication. The most commonly prescribed hormones are estrogens and progestagens (in... hormone production, cell regeneration and other biological activities linked to this 24 hour cycle.

The circadian rhythm is neither fully dependent nor fully independent of external cues such as sunlight and temperature. Early researchers identified that some sort of "internal" rhythm must exist, because plants and animals did not react immediately to artificially-induced changes in daily rhythms. However it has been well established that a mechanism for adjustment also exists, as plants and animals will eventually adjust their internal clock to a new pattern (if it is sufficiently regular).

It has also been clearly established that the circadian rhythm is rigidly linked to the light/dark cycle. Animals kept in total darkness for extended periods eventually demonstrate a "free running" rhythm. This research has influenced the design of Human spaceflight is space exploration with a human crew, and possibly passengers (in contrast to unmanned space missions, which are remotely-controlled or robotic space probes). Traditionally, these endeavours have been referred to as manned space missions, although today some prefer to use the term crewed or piloted space missions... spacecraft environments, as systems that mimic the light/dark cycle have been found to be highly beneficial to astronauts.

The circadian "clock" in Orders Subclass Monotremata Monotremata Subclass Marsupialia Didelphimorphia Paucituberculata Microbiotheria Dasyuromorphia Peramelemorphia Notoryctemorphia Diprotodontia Subclass Placentalia Xenarthra Dermoptera Desmostylia Scandentia Primates Rodentia Lagomorpha Insectivora Chiroptera Pholidota Carnivora Perissodactyla Artiodactyla Cetacea Afrosoricida Macroscelidea Tubulidentata Hyracoidea Proboscidea Sirenia The mammals are the class of vertebrate animals primarily characterized by the presence of mammary... mammals is primarily located in the The suprachiasmatic nucleus (SCN) is a nucleus in hypothalamus. It regulates the circadian rhythm. It consists of various cell types, some which possess ability for light-induced gene expression, they have direct connection to the retina via the so-called retino-hypothalamic tract. Rats with damage to SCN sleep erratically... suprachiasmatic nucleus (SCN), a distinct group of cells located in the In the anatomy of mammals, the hypothalamus is a region of the brain located below the thalamus, forming the major portion of the ventral region of the diencephalon and functioning to regulate certain metabolic processes and other autonomic activities. The hypothalamus links the nervous system to the endocrine system by... hypothalamus. Destruction of the SCN results in the complete absence of a circadian rhythm. Contributing to this clock are light receptors found in the Human eye cross-sectional view. Courtesy NIH National Eye Institute. Many animals have eyes different from the human eye. The retina is a thin layer of cells at the back of the eyeball of vertebrates and some cephalopods; it is the part of the eye which transduces light into neural... retina which have a pathway, (called the retinohypothalamic tract), leading to the SCN.

It appears that the SCN takes the information on day length from the retina, interprets it, and passes it on to the The pineal gland (pronunciation: pI-nE-&l, pI-), or , which existed in the Late Devonian Period, had an orifice on the top of the skull through which the pineal gland was exposed and received light input. Over the course of time and for unknown reasons, the pineal gland migrated... pineal gland (a pea-like structure found on the epithalamus), which then secretes the hormone Melatonin, or 5-methoxy-N-acetyltryptamine, is a hormone produced by pinealocytes in the pineal gland, located in the center of the brain. It is a derivative of the amino acid tryptophan. Melatonin helps regulate sleep-wake or circadian rhythms. Normally, production of melatonin by the pineal gland is stimulated... melatonin in response. Secretion of melatonin peaks at night and ebbs during the day. The SCN does not appear to be able to rapidly react to changes in the light/dark cues.

Recently, evidence has emerged that circadian rhythms are found in many cells in the body--outside of the SCN "master clock." Liver cells, for example, appear to respond to feeding rather than light. Cells from many parts of the body appear to have "free-running" rhythms.

Disruption to rhythms usually have a negative effect in the short term. Many travelers have experienced the condition known as Jet lag (or jet-lag) is a physical condition caused by crossing multiple time zones during flight. The condition is generally believed to be the result of disruption to the circadian rhythms (i.e. the light/dark cycle) of the body. It can also be exacerbated by experiencing sudden changes... jet lag, with its associated symptoms of Fatigue is a feeling of excessive tiredness or lethargy, with a desire to rest, perhaps to sleep. Often it causes yawning. It is typically the result of working, mental stress, jet lag or active recreation, but also from boredom or disease or simply lack of sleep. It may also have... fatigue, disorientation and Insomnia is a sleep disorder characterised by an inability to sleep and/or to remain asleep for a reasonable period during the night. Sufferers typically complain of being unable to close their eyes for more than a few minutes at a time, or of tossing and turning through the night... insomnia. A number of other Definition A sleep disorder is a disorder in the sleep patterns of a person or animal. Some sleep disorders can interfere with mental and emotional function, due to their interference with REM sleep. Common sleep disorders The most common sleep disorders include: Bruxism: The sufferer involuntarily grinds his or her... sleep disorders are associated with irregular or pathological functioning of the circadian rhythms.

Plant Circadian Rhythms

Plants, are This page is a candidate to be moved to Wiktionary. If the page can be expanded into an encyclopedic article, rather than a dictionary definition, please do so and remove this message. Otherwise, you can help by formatting it per the Wiktionary guidelines in preparation for the move. (Biology) Organism... sessile organisms and thus, they are intimatly associated with their environment. This ability to anticipate daily changes in temperature and light period is of great advantage to plants. At the most basic level, circadian rhythms are the cyclical expression of This stylistic schematic diagram shows a gene in relation to the double helix structure of DNA and to a chromosome (right). Introns are regions often found in eukaryote genes which are removed in the splicing process: only the exons encode the protein. This diagram labels a region of only 40... genes. This cyclical expression is controlled by a central clock, which responds to light as well as temperature inputs. For example, as the days grow shorter and cooler, plants are able to change the expression of their genes to prepare for the end of the growing season and to prepare for winter. The study of circadian rhythms is of particular interest for plant biologists. Many of the circadian controlled genes are involved in chilling and freezing tolerance. A better understanding of these genes will allow the creation of stress tolerant plants, better able to survive in cold temperatures. This will allow the expansion of both growing seasons and the growth range for many economically important crops.

See also

• Human factors is a term used mainly in the United States. In Europe and the rest of the world, the term ergonomics is more prevalent. Human factors is a profession that focuses on how people interact with products, tools, procedures, and any processes likely to be encountered in the modern... Human factors
• Human reliability