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The biological half-life of caffeine ..
Caffeine is also a common ingredient of soft drinks such as cola, originally prepared from kola nuts. Soft drinks typically contain about 10 to 50 milligrams of caffeine per serving. By contrast, energy drinks such as Red Bull can start at 80 milligrams of caffeine per serving. The caffeine in these drinks either originates from the ingredients used or is an additive derived from the product of decaffeination or from chemical synthesis. Guarana, a prime ingredient of energy drinks, contains large amounts of caffeine with small amounts of theobromine and theophylline in a naturally occurring slow-release excipient.24
(Note: Carrying our sleep research on student sleep patterns seems to be as valid as research on the sleep patterns of cats).
Other evaluation points
When we lose sleep and are given the opportunity to make it up we only catch up on a small proportion of it. This suggests that not all sleep is needed. Why therefore would we need non-essential sleep?
Amino acids are not stored in the body and only remain in the bloodstream for about eight hours before being broken down or excreted. As a result we would expect protein synthesis to stop half way through a night’s sleep. This would explain why deep sleep occurs in the first half of a night’s sleep. Of course this also assumes that we eat just prior to going to sleep!
Oswald (1980) and Hartman (1984) built on the theory to include restoration during REM sleep. They believe that REM is for restoration of the brain. Stern & Morgane (1974) believed that neurotransmitter levels within the brain may be restored during REM sleep. The young brain is growing and developing at its fastest rate so young children, especially babies sleep for much longer than adults. In the newborn about 9 hours a day is spent in REM compared to about 2 hours in adults.
Note: restoration theories of sleep make cognitive sense since we suffer so many unpleasant consequences when deprived of sleep
It is important to remember that this seeks to explain the biological state of REM sleep and makes no mention of the psychological state of dreaming. Therefore it is not to be used in a question that asks for theories of dreaming.
Research in support of restoration theories
The most obvious support comes from aspects of the sleep deprivation studies to be discussed in the next section. First some other evidence:
Protein Synthesis Evolution Ecology
Randy Gardner and Huber-Weisman (1976)
Research against restoration theories
· Protein synthesis occurs 24 hours a day, not just during stage 4 - although it does seem to peak in stage 4.
· Amount of sleep does not appear to decrease when our level of daytime activity decreases, (as shown by Ryback & Lewis and others).
and protein synthesis for repair and growth. However, these processes also occur whilst we are awake too!
Evidence in support of restoration theory
Further support is provided by Shapiro (1981) who studied ultra marathon runners who had completed a 57-mile run. It was found that they slept for 90 minutes longer than usual for the next two nights. REM sleep decreased whilst stage 4 of quiet or NREM sleep increased dramatically from 25% of nights sleep to 45%.
However, lack of exercise does not reduce amount of deep sleep as this model would predict. Repack and Lewis (1971) got healthy students to spend 6 weeks in bed and observed no change in their sleep patterns.
It is the world's most widely consumed psychoactive drug
In 1819, the German chemist Friedrich Ferdinand Runge isolated relatively pure caffeine for the first time. According to Runge, he did this at the behest of Johann Wolfgang von Goethe.39 In 1827, Oudry isolated "theine" from tea, but it was later proved by Mulder and Jobat that theine was the same as caffeine.39 The structure of caffeine was elucidated near the end of the 19th century by Hermann Emil Fischer, who was also the first to achieve its total synthesis.40 This was part of the work for which Fischer was awarded the Nobel Prize in 1902. The nitrogen atoms are all essentially planar (in sp2 orbital hybridization), resulting in the caffeine molecule's having aromatic character. Being readily available as a byproduct of decaffeination, caffeine is not usually synthesized.41 If desired, it may be synthesized from dimethylurea and malonic acid.42
Adenosine is found in every part of the body, because it plays a role in the fundamental ATP-related energy metabolism and is necessary for RNA synthesis, but it has special functions in the brain. There is a great deal of evidence that concentrations of brain adenosine are increased by various types of metabolic stress including anoxia and ischemia. The evidence also indicates that brain adenosine acts to protect the brain by suppressing neural activity and also by increasing blood flow through A2A and A2B receptors located on vascular smooth muscle.57 By counteracting adenosine, caffeine reduces resting cerebral blood flow between 22% and 30%.58 Caffeine also has a generally disinhibitory effect on neural activity. It has not been shown, however, how these effects cause increases in arousal and alertness.
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Synthesis and biosynthesis Synthesis
Despite the thousand years that have passed, there is still controversy surrounding the biological effects of coffee and it's primary active ingredient, caffeine.
Caffeine & Neurotransmitters - World of Caffeine
Phosphodiesterase inhibitors inhibit cAMP-phosphodiesterase (cAMP-PDE) enzymes, which convert cyclic AMP (cAMP) in cells to its noncyclic form, thus allowing cAMP to build up in cells. Cyclic AMP participates in activation of protein kinase A (PKA) to begin the phosphorylation of specific enzymes used in glucose synthesis. By blocking its removal, caffeine intensifies and prolongs the effects of epinephrine and epinephrine-like drugs such as amphetamine, methamphetamine, and methylphenidate. Increased concentrations of cAMP in parietal cells causes an increased activation of protein kinase A (PKA), which in turn increases activation of H+/K+ ATPase, resulting finally in increased gastric acid secretion by the cell. Cyclic AMP also increases the activity of the funny current, which directly increases heart rate. Caffeine is also a structural analogue of strychnine and, like it (though much less potent), a competitive antagonist at ionotropic glycine receptors.66
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