Circadian Rhythms

Topics: Sleep, Circadian rhythm, Melatonin Pages: 10 (3608 words) Published: September 17, 2013
1. Describe how circadian rhythms are associated with sleep deprivation. 2. Explain the results of the sleep deprivation assessment. 3. Do you agree, or disagree, with the results. Why, or why not? 4. If you are sleep deprived, what steps could you take to get more or better quality of sleep? Alternatively, if you are not sleep deprived, what techniques allow you to get quality sleep most nights of the week?

Circadian rhythms: Their role and dysfunction in affective disorder Press conference on the occasion of the 23rd ECNP Congress 2010, Amsterdam All humans are synchronised to the rhythmic light-dark changes that occur on a daily basis. Rhythms in physiological and biochemical processes and behavioural patterns persist in the absence of all external 24-hour signals from the physical environment, with a period that is close to 24 hours. These rhythms are referred to as ´circadian´, from the Latin ´circa diem´ (´about a day´), and are attributable to internal biological clocks, driven by a major circadian pacemaker in the brain. The circadian pacemaker is entrained each day to the 24-hour solar cycle, which is the major ´zeitgeber´ (literally time-giver). Other zeitgebers are food intake, activity, or social cues, e.g. the alarm clock. Good temporal entrainment allows for optimal performance at the right time of the day, because being able to anticipate future tasks allows the appropriate physiological and psychological preparation. However, our modern society often imposes deviations from the regular work-rest-scheme, as in shift work, which results in problems with entrainment. Failure to adapt to environmental and societal time cues leads to misalignment of internal biological clocks. This ´dysentrainment´ comes with enhanced risk of errors and accidents, loss of productivity, and health risks such as increased propensity for cancer, depression, sleep disturbances, gastrointestinal, metabolic and cardiovascular disorders, decreased immune responses and even life span. Hence, people with circadian rhythm disruption caused by shift work often develop glucose intolerance, diabetes and hypertension, and maybe cancer. The recent discovery of the core molecular circadian clock machinery has dramatically increased interest in the impact of circadian dysregulation on mental and physical health. Molecular basis of circadian rhythms

Circadian rhythms are directed by a master biological clock in a specific brain structure of the hypothalamus called the suprachiasmatic nuclei (SCN). Apart from the SCN, the body has circadian oscillators in all brain regions and peripheral tissues, for example the liver (Schulz & Steimer, 2009, Bechtold et al., 2010). The SCN is synchronised daily by environmental signals – mainly light (Wirz-Justice, 2006). Receiving information on lighting conditions directly from the retina, the SCN drives secretion of the pineal gland hormone melatonin as well as and many peripheral clocks, and their outputs modulate the SCN through feedback or feed-forward effects. Thus, in the body there is a hierarchy of interacting clocks (Schulz, 2007). In all cells, the expression of many genes changes rhythmically over 24 hours. Specific circadian genes such as CLOCK, BMAL1, and PER are responsible for the main SCN clockworking machinery as well as subsidiary clocks in other parts of the body. In mice with mutations in time-keeping genes, deviant circadian sleep-wake and other rhythms can be observed. In addition, new interest in the role of circadian dysregulation in psychiatric disorders has arisen from the finding that a mutation in a core circadian clock gene induces hyperactivity, decreased sleep, and mania-like behaviour in mice (Turek, 2008). Animal studies were the key development that brought the field to its present exciting position, because their findings suggested that ´clock genes´ are directing the circadian rhythms in all physiological processes. Circadian disturbances: clinical...
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