Information about Circadian Rhythm
A circadian rhythm is a roughly-24-hour cycle in the physiological processes of living beings, including plants, animals, fungi and cyanobacteria. The term "circadian", coined by Franz Halberg,[1] comes from the Latin circa, "around", and diem or dies, "day", meaning literally "about a day." The formal study of biological temporal rhythms such as daily, weekly, seasonal, and annual rhythms, is called chronobiology.
In a strict sense, circadian rhythms are endogenously generated, although they can be modulated by external cues such as sunlight and temperature.
The earliest known account of a circadian rhythm dates from the fourth century BC, when Androsthenes, in descriptions of the marches of Alexander the Great, described diurnal leaf movements of the tamarind tree.
The simplest known circadian clock is that of the prokaryotic cyanobacteria. Recent research has demonstrated that the circadian clock of Synechococcus elongatus can be reconstituted in vitro with just the three proteins of their central oscillator. This clock has been shown to sustain a 22 hour rhythm over several days upon the addition of ATP. Previous explanations of the prokaryotic circadian timekeeper were dependent upon a DNA transcription / translation feedback mechanism, and although this has not been shown to be the case, it is still believed to hold true for eukaryotic organisms. Indeed, although the circadian systems of eukaryotes and prokaryotes have the same basic architecture: input - central oscillator - output, they do not share any homology. This implies probable independent origins.
In 1971, Konopka and Benzer first identified a genetic component of the biological clock using the fruit fly as a model system. Three mutant lines of flies displayed aberrant behavior - one had a shorter period, another had a longer one and the third had none. All the three mutations mapped to the same gene and was baptised period. The same gene was identified to be defective in a sleep disorder called FASPS (Familial Advanced Sleep Phase Syndrome) in human beings thirty years later - underscoring the conserved nature of the molecular circadian clock through evolution. We now know many more genetic components of the biological clock. Their interactions results in an interlocked feedback loop of gene products resulting in periodic fluctuations that the cells of the body interpret as a specific time of the day.
Our understanding of the biological clock has come a long way from "Imagine It To Be A Sine Wave Generator". We now know that the molecular circadian clock can function within a single cell - i.e. it is cell autonomous. At the same time, different cells may talk to each other resulting in a synchronized and democratic output of electrical signaling. These may interface with endocrine glands of the brain to result in periodic release of hormones. The receptors for these hormones may be located far across the body and sychronize the peripheral clocks (such as those present in the liver). Thus, the information of the time of the day as determined by the eyes may travel to the clock in the brain and through that, clocks in the rest of the body may be synchronized. This is how behavior such as drinking water, sleep/wake and body temperature are coordinately controlled by the biological clock.
There are many health problems associated with a disturbance in the sleep circadian rhythm. These can be temporary or due to a lack in the circadian rhythm in the body. These include Seasonal Affective Disorder (SAD) where the rhythm is disturbed due to the change in length of day, delayed sleep phase syndrome (DSPS) which is caused by a circadian rhythm abnormality causing the sufferers body to want to sleep later than normal [2]
Circadian rhythms also play a part in the reticular activating system in the reticular formation.
Free running organisms still have a consolidated sleep-wake cycle when in an environment shielded from external cues, but the rhythm is not engrained and may become out of phase with other circadian, or ultradian rhythms such as temperature and digestion. This research has influenced the design of spacecraft environments, as systems that mimic the light/dark cycle have been found to be highly beneficial to astronauts.
The circadian "clock" in mammals is located in the suprachiasmatic nucleus (SCN), a distinct group of cells located in the hypothalamus. Destruction of the SCN results in the complete absence of a regular sleep/wake rhythm. The SCN receives information about illumination through the eyes. The retina of the eyes contains not only "classical" photoreceptors but also photoresponsive retinal ganglion cells. These cells, which contain a photo pigment called melanopsin, follow a pathway called the retinohypothalamic tract, leading to the SCN. If cells from the SCN are removed and cultured, they maintain their own rhythm in the absence of external cues.
It appears that the SCN takes the information on day length from the retina, interprets it, and passes it on to the pineal gland (a pea-like structure found on the epithalamus), which then secretes the hormone melatonin in response. Secretion of melatonin peaks at night and ebbs during the day.
Cells in the body that have their own rhythms are called peripheral oscillators. These tissues include the esophagus, lung, liver, spleen and thymus. There is some evidence the olfactory bulb and prostate may also experience oscillations when cultured, suggesting these structures may also be weak oscillators.
Disruption to rhythms in the longer term is believed to have significant adverse health consequences on peripheral organs outside the brain, particularly in the development or exacerbation of cardiovascular disease. Timing of treatment in coordination with the body clock may significantly increase efficacy, and reduce drug toxicity, or adverse reactions. For example, timing treatment of angiotensin converting enzyme inhibitors (ACEi) may reduce nocturnal blood pressure, also benefit left ventricular (reverse) remodeling.
Moreover, genetic manipulations of clock genes profoundly affect cocaine's actions.[7]
In addition to light intensity, wavelength (or color) of light is an important factor in the degree to which the clock is reset. Melanopsin is most efficiently excited by blue light (420-440 nm).[8]
By depriving people of daylight and other external time cues, scientists have learned that most people's biological clocks work on a 25-hour cycle when subjects are allowed to use electric light at will. But because daylight or other lighting can reset circadian rhythms, our biological cycles normally follow the 24-hour cycle of the earth's rotation, rather than our innate cycle which averages 24 hours and 11 minutes for adults.[9] Circadian rhythms can be affected to some degree by almost any kind of external time cue, such as the beeping of an alarm clock, the clatter of a garbage truck, or the timing of meals. Scientists call external time cues zeitgebers (German for "time givers").[10]
In a strict sense, circadian rhythms are endogenously generated, although they can be modulated by external cues such as sunlight and temperature.
History
The first endogenous circadian oscillation was observed in the 1700s by the French scientist Jean-Jacques d'Ortous de Mairan who noticed that 24-hour patterns in the movement of the leaves of the plant Mimosa pudica continued even when the plants were isolated from external stimuli.The earliest known account of a circadian rhythm dates from the fourth century BC, when Androsthenes, in descriptions of the marches of Alexander the Great, described diurnal leaf movements of the tamarind tree.
Criteria
General criteria of circadian rhythms- The rhythm persists in constant conditions (for example constant dark) with a period of about 24 hours: The rationale for this criterion is to distinguish circadian rhythms from those "apparent rhythms" that merely respond to external periodic cues. For example, the behavior of wearing sunglasses would not be classified as a circadian rhythm - if there were no sunlight, the behavior would not persist.
- The rhythm has the same period over a range of temperatures (i.e. it is temperature compensated): The rationale for this criterion is to distinguish circadian rhythms from other biological rhythms arising due to circular nature of a reaction pathway - for instance Kreb's cycle in metabolism. At a low enough or high enough temperature, the period of the circular reaction may reach 24 hours, but it would be merely coincidental and not by design.
- The rhythm can be reset by exposure to an external stimulus: The rationale for this criterion is to distinguish circadian rhythms from other imaginable endogenous 24 hour rhythms that are immune to resetting by external cues and hence do not serve the purpose of estimating the local time. Your wrist watch has no means of determining the local time - but your biological clock does.
Origin
Circadian rhythms are believed to have originated in the earliest cells, with the purpose of protecting replicating DNA from high ultraviolet radiation during the daytime. As a result, replication was relegated to the dark. The fungus Neurospora, which exists today, retains this clock-regulated mechanism.The simplest known circadian clock is that of the prokaryotic cyanobacteria. Recent research has demonstrated that the circadian clock of Synechococcus elongatus can be reconstituted in vitro with just the three proteins of their central oscillator. This clock has been shown to sustain a 22 hour rhythm over several days upon the addition of ATP. Previous explanations of the prokaryotic circadian timekeeper were dependent upon a DNA transcription / translation feedback mechanism, and although this has not been shown to be the case, it is still believed to hold true for eukaryotic organisms. Indeed, although the circadian systems of eukaryotes and prokaryotes have the same basic architecture: input - central oscillator - output, they do not share any homology. This implies probable independent origins.
In 1971, Konopka and Benzer first identified a genetic component of the biological clock using the fruit fly as a model system. Three mutant lines of flies displayed aberrant behavior - one had a shorter period, another had a longer one and the third had none. All the three mutations mapped to the same gene and was baptised period. The same gene was identified to be defective in a sleep disorder called FASPS (Familial Advanced Sleep Phase Syndrome) in human beings thirty years later - underscoring the conserved nature of the molecular circadian clock through evolution. We now know many more genetic components of the biological clock. Their interactions results in an interlocked feedback loop of gene products resulting in periodic fluctuations that the cells of the body interpret as a specific time of the day.
Our understanding of the biological clock has come a long way from "Imagine It To Be A Sine Wave Generator". We now know that the molecular circadian clock can function within a single cell - i.e. it is cell autonomous. At the same time, different cells may talk to each other resulting in a synchronized and democratic output of electrical signaling. These may interface with endocrine glands of the brain to result in periodic release of hormones. The receptors for these hormones may be located far across the body and sychronize the peripheral clocks (such as those present in the liver). Thus, the information of the time of the day as determined by the eyes may travel to the clock in the brain and through that, clocks in the rest of the body may be synchronized. This is how behavior such as drinking water, sleep/wake and body temperature are coordinately controlled by the biological clock.
Animal circadian rhythms
Circadian rhythms are important in determining the sleeping and feeding patterns of all animals, including human beings. There are clear patterns of brain wave activity, hormone production, cell regeneration and other biological activities linked to this daily cycle.There are many health problems associated with a disturbance in the sleep circadian rhythm. These can be temporary or due to a lack in the circadian rhythm in the body. These include Seasonal Affective Disorder (SAD) where the rhythm is disturbed due to the change in length of day, delayed sleep phase syndrome (DSPS) which is caused by a circadian rhythm abnormality causing the sufferers body to want to sleep later than normal [2]
Circadian rhythms also play a part in the reticular activating system in the reticular formation.
Impact of light-dark cycle
The rhythm is linked to the light-dark cycle. Animals kept in total darkness for extended periods eventually function with a "free-running" rhythm. Each "day," their sleep cycle is pushed back or forward (depending on whether the endogenous period is longer or shorter than 24 hours). The environmental cues that each day reset the rhythms are called Zeitgebers (German, literally "Time Givers"). Interestingly, totally blind subterranean mammals (e.g., blind mole rat Spalax sp.) are able to maintain their endogenous clock in absence of the external stimuli.Free running organisms still have a consolidated sleep-wake cycle when in an environment shielded from external cues, but the rhythm is not engrained and may become out of phase with other circadian, or ultradian rhythms such as temperature and digestion. This research has influenced the design of spacecraft environments, as systems that mimic the light/dark cycle have been found to be highly beneficial to astronauts.
Suprachiasmatic nucleus
The circadian system can be divided into three major components: the central oscillator or pacemaker; the afferent pathways which carry entraining environmental information to the oscillator; and the efferent pathways that communicate the rhythmicity of the oscillator to the physiology and behavior of the organism.[3]The circadian "clock" in mammals is located in the suprachiasmatic nucleus (SCN), a distinct group of cells located in the hypothalamus. Destruction of the SCN results in the complete absence of a regular sleep/wake rhythm. The SCN receives information about illumination through the eyes. The retina of the eyes contains not only "classical" photoreceptors but also photoresponsive retinal ganglion cells. These cells, which contain a photo pigment called melanopsin, follow a pathway called the retinohypothalamic tract, leading to the SCN. If cells from the SCN are removed and cultured, they maintain their own rhythm in the absence of external cues.
It appears that the SCN takes the information on day length from the retina, interprets it, and passes it on to the pineal gland (a pea-like structure found on the epithalamus), which then secretes the hormone melatonin in response. Secretion of melatonin peaks at night and ebbs during the day.
Outside the SCN "master clock"
Recently, evidence has emerged that circadian rhythms are found in many cells in the body outside the SCN "master clock." Furthermore, liver cells, for example, appear to respond to feeding rather than to light. Cells from many parts of the body appear to have "free-running" rhythms.Cells in the body that have their own rhythms are called peripheral oscillators. These tissues include the esophagus, lung, liver, spleen and thymus. There is some evidence the olfactory bulb and prostate may also experience oscillations when cultured, suggesting these structures may also be weak oscillators.
Disruption
Disruption to rhythms usually has a negative effect in the short term. Many travelers have experienced the condition known as jet lag, with its associated symptoms of fatigue, disorientation and insomnia. A number of other disorders, for example bipolar disorder and some sleep disorders are associated with irregular or pathological functioning of circadian rhythms. Recent research suggests that circadian rhythm disturbances found in bipolar disorder are positively influenced by lithium's effect on clock genes.[4]Disruption to rhythms in the longer term is believed to have significant adverse health consequences on peripheral organs outside the brain, particularly in the development or exacerbation of cardiovascular disease. Timing of treatment in coordination with the body clock may significantly increase efficacy, and reduce drug toxicity, or adverse reactions. For example, timing treatment of angiotensin converting enzyme inhibitors (ACEi) may reduce nocturnal blood pressure, also benefit left ventricular (reverse) remodeling.
Relationship to cocaine
In addition, circadian rhythms and clock genes expressed in brain regions outside the SCN may significantly influence the effects produced by drugs such as cocaine.[5][6]Moreover, genetic manipulations of clock genes profoundly affect cocaine's actions.[7]
Light and the biological clock
Light resets the biological clock in accordance with the phase response curve(PRC). Depending on the timing, light can advance or delay the circadian rhythm. Both the PRC and the required illuminance vary from species to species; much lower light levels are required to reset the clocks in nocturnal rodents than in humans.In addition to light intensity, wavelength (or color) of light is an important factor in the degree to which the clock is reset. Melanopsin is most efficiently excited by blue light (420-440 nm).[8]
By depriving people of daylight and other external time cues, scientists have learned that most people's biological clocks work on a 25-hour cycle when subjects are allowed to use electric light at will. But because daylight or other lighting can reset circadian rhythms, our biological cycles normally follow the 24-hour cycle of the earth's rotation, rather than our innate cycle which averages 24 hours and 11 minutes for adults.[9] Circadian rhythms can be affected to some degree by almost any kind of external time cue, such as the beeping of an alarm clock, the clatter of a garbage truck, or the timing of meals. Scientists call external time cues zeitgebers (German for "time givers").[10]
See also
- Chronobiology
- Human factors
- Human reliability
- Actigraphy
- Circadian rhythm sleep disorders
- Advanced sleep phase syndrome (ASPS) and Family Advanced sleep phase syndrome (FASPS)
- Jet lag
Notes
1. ^ [1] Halberg Chronobiology Center
2. ^ Circadian Rhythms and Sleep. Circadian Rhythms and Sleep. Serendip (October 2007). Retrieved on 2007-09-19.
3. ^ Hormonal and Pharmacological Manipulation of the Circadian Clock: Recent Developments and Future Strategies. Worldwide project on sleep and health. Retrieved on 2007-09-19.
4. ^ [2]
5. ^ Uz T, Akhisaroglu M, Ahmed R, Manev H (2003). "The pineal gland is critical for circadian Period1 expression in the striatum and for circadian cocaine sensitization in mice". Neuropsychopharmacology 28 (12): 2117-23. PMID 12865893.
6. ^ Kurtuncu M, Arslan A, Akhisaroglu M, Manev H, Uz T (2004). "Involvement of the pineal gland in diurnal cocaine reward in mice". Eur J Pharmacol 489 (3): 203-5. PMID 15087244.
7. ^ McClung C, Sidiropoulou K, Vitaterna M, Takahashi J, White F, Cooper D, Nestler E (2005). "Regulation of dopaminergic transmission and cocaine reward by the Clock gene". Proc Natl Acad Sci U S A 102 (26): 9377-81. PMID 15967985.
8. ^ Newman LA, Walker MT, Brown RL, Cronin TW, Robinson PR: "Melanopsin forms a functional short-wavelength photopigment", Biochemistry. 2003 Nov 11;42(44):12734-8.
9. ^ Human Biological Clock Set Back an Hour (1999). Retrieved on 2007-09-23.
10. ^ Circadian rhythms. Rapid eye movement (REM) sleep. Armenian Medical Network (2007). Retrieved on 2007-09-23.
2. ^ Circadian Rhythms and Sleep. Circadian Rhythms and Sleep. Serendip (October 2007). Retrieved on 2007-09-19.
3. ^ Hormonal and Pharmacological Manipulation of the Circadian Clock: Recent Developments and Future Strategies. Worldwide project on sleep and health. Retrieved on 2007-09-19.
4. ^ [2]
5. ^ Uz T, Akhisaroglu M, Ahmed R, Manev H (2003). "The pineal gland is critical for circadian Period1 expression in the striatum and for circadian cocaine sensitization in mice". Neuropsychopharmacology 28 (12): 2117-23. PMID 12865893.
6. ^ Kurtuncu M, Arslan A, Akhisaroglu M, Manev H, Uz T (2004). "Involvement of the pineal gland in diurnal cocaine reward in mice". Eur J Pharmacol 489 (3): 203-5. PMID 15087244.
7. ^ McClung C, Sidiropoulou K, Vitaterna M, Takahashi J, White F, Cooper D, Nestler E (2005). "Regulation of dopaminergic transmission and cocaine reward by the Clock gene". Proc Natl Acad Sci U S A 102 (26): 9377-81. PMID 15967985.
8. ^ Newman LA, Walker MT, Brown RL, Cronin TW, Robinson PR: "Melanopsin forms a functional short-wavelength photopigment", Biochemistry. 2003 Nov 11;42(44):12734-8.
9. ^ Human Biological Clock Set Back an Hour (1999). Retrieved on 2007-09-23.
10. ^ Circadian rhythms. Rapid eye movement (REM) sleep. Armenian Medical Network (2007). Retrieved on 2007-09-23.
Further reading
- Aschoff J (ed.) (1965) Circadian Clocks. North Holland Press, Amsterdam
- Avivi A, Albrecht U, Oster H, Joel A, Beiles A, Nevo E. 2001. Biological clock in total darkness: the Clock/MOP3 circadian system of the blind subterranean mole rat. Proc Natl Acad Sci USA 98:13751- 13756.
- Avivi A, Oster H, Joel A, Beiles A, Albrecht U, Nevo E. 2002. Circadian genes in a blind subterranean mammal II: conservation and uniqueness of the three Period homologs in the blind subterranean mole rat, Spalax ehrenbergi superspecies. Proc Natl Acad Sci USA 99:11718-11723.
- Ditty JL, Williams SB, Golden SS (2003) A cyanobacterial circadian timing mechanism. Annu Rev Genet 37:513-543
- Dunlap JC, Loros J, DeCoursey PJ (2003) Chronobiology: Biological Timekeeping. Sinauer, Sunderland
- Dvornyk V, Vinogradova ON, Nevo E (2003) Origin and evolution of circadian clock genes in prokaryotes. Proc Natl Acad Sci USA 100:2495-2500
- Koukkari WL, Sothern RB (2006) Introducing Biological Rhythms. Springer, New York
- Martino T, Arab S, Straume M, Belsham DD, Tata N, Cai F, Liu P, Trivieri M, Ralph M, Sole MJ. Day/night rhythms in gene expression of the normal murine heart. J Mol Med. 2004 Apr;82(4):256-64. Epub 2004 Feb 24. PMID: 14985853
- Refinetti R (2006) Circadian Physiology, 2nd ed. CRC Press, Boca Raton
- Takahashi JS, Zatz M (1982) Regulation of circadian rhythmicity. Science 217:1104–1111
- Tomita J, Nakajima M, Kondo T, Iwasaki H (2005) No transcription–translation feedback in circadian rhythm of KaiC phosphorylation. Science 307: 251–254
External links
- Circadian rhythm at the Open Directory Project
- www.circadian.org
- Biological Clocks A description of circadian rhythms in plants by de Mairan, Linnaeus, and Darwin
- Darkness Unveils Vital Metabolic Fuel Switch Between Sugar and Fat (html) (english). The University of Texas Health Science Center (2006-01-18). Retrieved on 2007-10-17.
- Circadian clocks go in vitro: purely post-translational oscillators in cyanobacteria
- Journal of Biological Rhythms
Plantae
Haeckel, 1866[1]
Divisions
Green algae
..... Click the link for more information.
Haeckel, 1866[1]
Divisions
Green algae
- Chlorophyta
- Charophyta
- Non-vascular land plants (bryophytes)
..... Click the link for more information.
Editing of this page by unregistered or newly registered users is currently disabled until (UTC) due to vandalism.
If you are prevented from editing this page, and you wish to make a change, please discuss changes on the talk page, request unprotection, log in, or
..... Click the link for more information.
If you are prevented from editing this page, and you wish to make a change, please discuss changes on the talk page, request unprotection, log in, or
..... Click the link for more information.
Eukarya
Whittaker & Margulis, 1978
(unranked) Opisthokonta
Kingdom: Fungi
(L., 1753) R.T. Moore, 1980[1]
Subkingdom/Phyla
..... Click the link for more information.
Whittaker & Margulis, 1978
(unranked) Opisthokonta
Kingdom: Fungi
(L., 1753) R.T. Moore, 1980[1]
Subkingdom/Phyla
- Chytridiomycota
- Blastocladiomycota
..... Click the link for more information.
Cyanobacteria
Orders
The taxonomy is currently under revision.[1]
Cyanobacteria (Greek: κυανόs (kyanós) = blue + bacterium) also known as Cyanophyta
..... Click the link for more information.
Orders
The taxonomy is currently under revision.[1]
Cyanobacteria (Greek: κυανόs (kyanós) = blue + bacterium) also known as Cyanophyta
..... Click the link for more information.
Franz Halberg is a scientist and the founder of modern chronobiology. He first began his experiments in the 1940s and later founded the Chronobiology Laboratories at the University of Minnesota.
..... Click the link for more information.
..... Click the link for more information.
Latin}}}
Official status
Official language of: Vatican City
Used for official purposes, but not spoken in everyday speech
Regulated by: Opus Fundatum Latinitas
Roman Catholic Church
Language codes
ISO 639-1: la
ISO 639-2: lat
..... Click the link for more information.
Official status
Official language of: Vatican City
Used for official purposes, but not spoken in everyday speech
Regulated by: Opus Fundatum Latinitas
Roman Catholic Church
Language codes
ISO 639-1: la
ISO 639-2: lat
..... Click the link for more information.
Chronobiology is a field of science that examines periodic (cyclic) phenomena in living organisms and their adaptation to solar and lunar related rhythms.[1] These cycles are known as biological rhythms.
..... Click the link for more information.
..... Click the link for more information.
The word endogenous means "arising from within", the opposite of exogenous.
..... Click the link for more information.
Biology
Endogenous substances are those that originate from within an organism, tissue, or cell [1] ...... Click the link for more information.
Sunlight, in the broad sense, is the total spectrum of the electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the atmosphere, and the solar radiation is obvious as daylight when the Sun is above the horizon.
..... Click the link for more information.
..... Click the link for more information.
trillion fold).]]
Temperature is a physical property of a system that underlies the common notions of hot and cold; something that is hotter generally has the greater temperature. Temperature is one of the principal parameters of thermodynamics.
..... Click the link for more information.
Temperature is a physical property of a system that underlies the common notions of hot and cold; something that is hotter generally has the greater temperature. Temperature is one of the principal parameters of thermodynamics.
..... Click the link for more information.
Jean-Jacques d'Ortous de Mairan (November 26, 1678 – February 20, 1771) was a French geophysicist.
He was born in the town of Béziers. His father, François d'Ortous, belonged to the landed gentry, but he died when Jean-Jacques was four.
..... Click the link for more information.
He was born in the town of Béziers. His father, François d'Ortous, belonged to the landed gentry, but he died when Jean-Jacques was four.
..... Click the link for more information.
M. pudica
Binomial name
Mimosa pudica
L.
The Sensitive plant (Mimosa pudica L.
..... Click the link for more information.
Binomial name
Mimosa pudica
L.
The Sensitive plant (Mimosa pudica L.
..... Click the link for more information.
citric acid cycle, also known as the tricarboxylic acid (TCA) cycle, the Krebs cycle, or Szent-Györgyi-Krebs cycle (after Hans Adolf Krebs and Albert Szent-Györgyi who first determined the chemical intermediates and reaction sequence of the cycle), is a series
..... Click the link for more information.
..... Click the link for more information.
Ultraviolet (UV) light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than soft X-rays. It is so named because the spectrum starts with wavelengths slightly shorter than the wavelengths humans identify as the color violet
..... Click the link for more information.
..... Click the link for more information.
Neurospora
Species
N. crassa
N. intermedia
N. sitophila
N. tetrasperma
Neurospora is a genus of fungi. The genus name, meaning "nerve spore" refers to the characteristic striations on the spores that resemble axons.
..... Click the link for more information.
Species
N. crassa
N. intermedia
N. sitophila
N. tetrasperma
Neurospora is a genus of fungi. The genus name, meaning "nerve spore" refers to the characteristic striations on the spores that resemble axons.
..... Click the link for more information.
Cyanobacteria
Orders
The taxonomy is currently under revision.[1]
Cyanobacteria (Greek: κυανόs (kyanós) = blue + bacterium) also known as Cyanophyta
..... Click the link for more information.
Orders
The taxonomy is currently under revision.[1]
Cyanobacteria (Greek: κυανόs (kyanós) = blue + bacterium) also known as Cyanophyta
..... Click the link for more information.
Adenosine 5'-triphosphate (ATP) is a multifunctional nucleotide that is most important as a "molecular currency" of intracellular energy transfer. In this role, ATP transports chemical energy within cells for metabolism.
..... Click the link for more information.
..... Click the link for more information.
Prokaryotes (IPA: /prəʊˈkæriəʊtiz/) are a group of organisms that lack a cell nucleus (= karyon), or any other membrane-bound organelles.
..... Click the link for more information.
..... Click the link for more information.
Editing of this page by unregistered or newly registered users is currently disabled due to vandalism.
If you are prevented from editing this page, and you wish to make a change, please discuss changes on the talk page, request unprotection, log in, or .
..... Click the link for more information.
If you are prevented from editing this page, and you wish to make a change, please discuss changes on the talk page, request unprotection, log in, or .
..... Click the link for more information.
Identifiers
Symbol PER2
Entrez 8864
HUGO 8846
OMIM 603426
RefSeq NM_003894
UniProt O15055
Other data
Locus Chr. 2 q37.3 Period (per
..... Click the link for more information.
Symbol PER2
Entrez 8864
HUGO 8846
OMIM 603426
RefSeq NM_003894
UniProt O15055
Other data
Locus Chr. 2 q37.3 Period (per
..... Click the link for more information.
Sleep is the state of natural rest observed throughout the animal kingdom, in all mammals and birds, and in many reptiles, amphibians, and fish.
In humans, other mammals, and many other animals that have been studied — such as fish, birds, ants, and fruit-flies —
..... Click the link for more information.
In humans, other mammals, and many other animals that have been studied — such as fish, birds, ants, and fruit-flies —
..... Click the link for more information.
Electroencephalography is the neurophysiologic measurement of the electrical activity of the brain by recording from electrodes placed on the scalp or, in special cases, subdurally or in the cerebral cortex.
..... Click the link for more information.
..... Click the link for more information.
hormone (from Greek όρμή - "to set in motion") is a chemical messenger that carries a signal from one cell (or group of cells) to another. All multicellular organisms produce hormones (including plants - see phytohormone).
..... Click the link for more information.
..... Click the link for more information.
Seasonal affective disorder, also known as winter depression, is an affective, or mood, disorder. Most SAD sufferers experience normal mental health throughout most of the year, but experience depressive symptoms in the winter or summer.
..... Click the link for more information.
..... Click the link for more information.
The reticular activating system is the name given to the part of the brain (the reticular formation and its connections) believed to be the center of arousal and motivation in animals (including humans).
..... Click the link for more information.
..... Click the link for more information.
The reticular formation is a part of the brain which is involved in stereotypical actions, such as walking, sleeping, and lying down. It is essential for governing some of the basic functions of higher organisms, and phylogenetically one of the oldest portions of the brain.
..... Click the link for more information.
..... Click the link for more information.
Free-running sleep is sleep that is not artificially regulated. It is used as a form of chronotherapy that can help to cure some sleep disorders. Most people in the industrial world cannot afford free-running sleep.
..... Click the link for more information.
..... Click the link for more information.
Zeitgeber (from German for "time giver") is any external (exogenous) cue that entrains the internal (endogenous) time keeping system of organisms. The strongest Zeitgeber, for both plants and animals, is light.
..... Click the link for more information.
..... Click the link for more information.
Ultradian characterizes recurrent periods or cycles repeated frequently throughout a 24-hour day
The descriptive term ultradian is used in sleep research to describe individual stages of sleep that occur within intervals of an organism's circadian rhythm, and especially to
..... Click the link for more information.
The descriptive term ultradian is used in sleep research to describe individual stages of sleep that occur within intervals of an organism's circadian rhythm, and especially to
..... Click the link for more information.
trillion fold).]]
Temperature is a physical property of a system that underlies the common notions of hot and cold; something that is hotter generally has the greater temperature. Temperature is one of the principal parameters of thermodynamics.
..... Click the link for more information.
Temperature is a physical property of a system that underlies the common notions of hot and cold; something that is hotter generally has the greater temperature. Temperature is one of the principal parameters of thermodynamics.
..... Click the link for more information.
This article is copied from an article on Wikipedia.org - the free encyclopedia created and edited by online user community. The text was not checked or edited by anyone on our staff. Although the vast majority of the wikipedia encyclopedia articles provide accurate and timely information please do not assume the accuracy of any particular article. This article is distributed under the terms of GNU Free Documentation License.
Herod_Archelaus
