Biological rhythms and sleep

Biological rhythms and sleep explanations

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  • Created on: 08-06-12 15:04


Circadian rhythms- approx 24 hours e.g sleep/wake cycle. Run by pacemakers & corrected by zietgerbers.Siffre- Spend 179 days in cave in the absense of exogenous zeitgerber natural light. His sleep/wake cycle extended and temperature cycle because desynronized. Suggesting 2 seperate endogenous pacemakers. This was a study of one unique man so can't be generalised. Further support for sleep/wake cycle --> Aschoff & Wever pps place in underground bunker in absense of external cues circadium rhythm extended 25-29hrs. More reliable findings as a larger sample use. Shows external cues are important to regulate biological clocks with outside world. Flaws found in research --> Czeisler was able to alter pps circadian rhythm down to 22-28 hours with dim lighting. Affects validity of earlier research. There are individual differences some people need 4 hours sleep; others 10 and lifespan changes. Duffy found diff. innate patterns 'larks' & 'owls'

Temp. 36 degrees c at 4.30am- 38 at 6.30pm. Follard- learning ability of 3 yr olds; read stories at 9am/3pm. 3pm group superior recall, retaining 8% more info at higher body temp. Research is correlational can't establish cause & effect is increase cognitive performance due to temperature or does high temp lead to high arousal. Extraneous variable e.g food, diff. abilities

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Ultradian & Infradian

Ultradian- more than 1 cycle a day .Sleep stages: Awake- Beta. Stage 1.Relaxed- alpha. 2. Heart rate slows more- theta. Sleep spindles 3. Deep sleep SWS Delta Waves. Metabolic rate slows & growth hormone produced 4. Larger Delta waves. Very hard to awake. REM sleep- paradoxical sleep- associated with dreaming. Cycles approx 90 mins long and 5 a night.

Infradian- Menstrual cycle & hibernation. Menstrual cycle is determined by fluctuation of hormones

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Endogenous pacemakers

Present a genetically inherited mechanism (emphasizes nature over nurture). A key biological clock is the suprachaismatic nucleus in the hypathalum. PERIOD 3 is one of the clocks which influences our biological clock; comes in different forms, each producing a slightly different pattern. Explains individual variation (long/short sleeping 'lark'/'owl'.)

Stephan & Zucker -> If the SCN in normal animals is lesioned, circadian rhythm of sleep/wake and temp. is completely disrupted showing SCN importance as internal clock. Cautious when generalising but can be fairly sure the SCN and pineal works in similar way. For ethical reason can't lesion humans but can do free-running studies. Siffre--> sleep/waking cycle erratic but eventual settled to 25-32 hours and body temp extented. Pacemakers run slower than 24 hrs and need daily synronising. Both cycles desynronised implying seperate pacemakers. Good long study allowing cycle to settle, but extranous variable e.g temp, lack of social interaction & not reliable alone. But support from Aschoff and Wever so more reliable. Replicated findings- how science works. Explanation is reductionist- offering lowest of physiological mechanisms underestimating contribution of social zeitgerbersLight & SCN & pineal- retina is connected to SCN. Retinohypothalamatic tract. SCN recieves info about amt light reaching retina. SCN is also connected by a pathway to the pineal gland. SCN regulates pineals activity of producing melatonin. Melatonin is linked with sleeping (Abraham- produce sleep in sparrows- careful about generalising to humans diff. process pineal gland responds directly to light penetrating skull bone). More melatonin produced in evening; reduced in morning. Unlikely the SCN-pineal system looks after all biological rhythms. Damage to SCN doesnt affect meal time in rats (Rosenwasser) so must be controlled by another pacemaker. Menstrual cycle doesnt respond to light seems to be completely relying on pacemaker.

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Exogenous zeitgerbers

Exogenous zeitgerber are external cues e.g light and noise which regulate endogenous pacemakers with the outside world. However there are important factors.

Artificial light & sleeping habits -> not determined by darkness due to electricity. Before invention sleep/waking would be governed by light/darkness which is adaptive and promotes survival. Changes in zeitgerbers are recently recent in human social evolution

Work and social habits- Some places in Greenland have 24 hrs light/darkness yet they maintain normal cycles of sleep. So social and work habits are used to synronise the sleep/waking pacemaker with outside world

Zeitgerbers and pacemakers need to interact together supports interactism approach. Light is key zeitgerber that helps synronise pacemaker with outside world.

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Disruption of biological rhythms- jet lag

Jet lag can cause pacemaker to become desynronised from zeitgerber. Worse when travelling West to East (phase advance) Symptoms include tiredness, poor concentrating, irritability and anxiety. These can last couple hours- days. Jet lag can be explained through interaction of pacemakers and zietgerbers (light). When going East to West phase delay, our body clock is ahead of local time and has to wait for external cues to catch up i.e body clock tells you it is 7pm but its only 2pm. When going West to East phase advance our body clock thinks its 7pm but its actually 12pm. Out body clock is behind time and not ready to sleep- in needs to catch up. It seems phase advance is harder to adjust to and symptoms are worse.The SCN will gradually change to the adjusted time of day in its new environment, but it can take time and dysynronization several days but their are individual differences

Recht- over 3yrs baseball team won 37% games travelling West-East and 44% East- West. Jet lag affected performance and worse after phase advance. But there are uncontrolled variables; ability of teams, fluctuations of forms and injury so not very valid. But support from American servicemen- took 3 days to recover phase delay and 8 for phase advance. (Correlational cant establish cause & effect however accumulation of evidence and knowledge of rhythms produce convicing picture.                Regular travellers- Cabin Crew. Cho- raised stress hormones and worse memory than controls and shrinkage of temporal lobe. Waterhouse - decrease cognitive performance and psychosi                        Other factors affected severity: individual differences some people more sensitve to jet lag, may be related to circadium clock gene PERIOD 3. Each form produces slightly diff. circadian pattern. Age; decreases with age; Sack; but inconsistant findings. Coping strategies -Arendt- bright light & melatonin tablets. Melatonin reduce jet lag but needs to be taken at certain times in circadian cycle and depends on advance/delay same for bright light. Most reliable method is to adapt to local zeitgerbers. (real life apps)

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Disruption of biological rhythms- shift work

Requires being active when body clock imposes we sleep. Electrical light meant businesses could operate 24/7. Acceptable to alternate unsociable shifts. Typical pattern 12am-8am, 8am-4pm & 4pm-12am; typically 1 week per shift. Standard pattern was backward rotation. Sleep is important function in diurnal animal. SCN extremely sensitive to light; key element of sleep control network as melatonin has direct effects on brainstem sleep centres. Working at 2am goes against circadium rhythm; maintaining alertness when sleep centres impose sleep. So hard to maintain concentration and consequences. Chernobyl ;shift workers failing to notice key warning signals at 1.30 am; attention worst and fighting off drive to sleep. But it was uncontrolled in scientific terms; dont know all variable so unreliable. Gold-> self report nurses on night shift more road accidents. Davis-> linked to breast cancer development and heart disease.

Western society depend on shift work but can cope be devising methods. Czeisler studied Utah chemical plant. Workers were stressed/absent/ sleeping troubles. Using biological rhythm knowledge devised forward rotation (like phase delay) and extend their day abit; easier to stay up longer than go bed earlier. Needed longer to resynchronise clock with external cues so 21 days. After 9 months results assessed; fewer health/stress/ absent problems & higher productivity. Application of science. Coren- american police officers changed to forward rotation of 18 day shifts; 40% reduction in accidents. Replication key how science work.

Research in disruption of rhythms leads to applications for reducing disruption (Cziesler). Shows how social, cultural and technological evolution increased strain on inherited systems for controlling rhythms which become disrupted.  Daytime sleep is likely to be less restorative with disruptions, so night workers may suffer mild sleep deprivation as well as trying to stay alert these problems complicate interpretion of research studies as effects of shift work may be confounding with effects of sleep deprivation- need to be cautious about drawing conclusions (validity)

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Lifespan changes

Age-related changes; at birth babies sleep 15 hours; 50%-60% REM. Older children a pattern of 9 hours emerges with 20-25% REM. Early changes most dramatic. Ohayon- identified gradual changes over rest of lifespan. Deep NREM decreases from about 24% (age 5)- 9% (age 70). REM decreases from 25% (age 5) - 19% (age 70). Slight increases in 1&2 NREM. Decrease in total sleep time from 8 hrs at 5 - 6 hour at 70. Adolescent sleep patterns- time of major brain changes, reorganising neural pathways and synapses. Changes to daily activity e,g work, social networking taking up more time. Evidence this shifts sleeping patterns; less sleep in week & more at weekend, and sleeping less overall than adults. Suggested school should start later allowing time to catch up (Wolfson). If REM and deep NREM is associated with brain growth & development is a good suggestion.

For newborns high % REM explained as its a rapid time for brain growth; especially new synaptic connections; large amt infor being processed; experiencing and learning for 1st time. As time goes by rate of brain growth and learning slows. So if REM associated to brain growth and learning it would also decrease (support by continual decline of REM). Lifespan reduction of NREM harder to explain; stages 3-4 linked with brain restoration and important for cog. processing. The gradual loss of this may be natural aging which explains decline in cog. abilities in old age.

Changes provide clues into function e.g Newborns & REM. Sign. Individual differences 4-10 hrs; which cannot be explained. Individual preferance to sleep pattern is somnotypology which are increasingly being factored into research to control extraneous variables Sleep patterns can be affected by outside factors. Its been suggested disrupted sleep in elderly is due to illnes/medication, so scientific research need to be careful to control factors

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Functions of sleep- evolutionary

Basic principle of evolution that behaviours that are not adaptive are 'selected out' during evolution, so if sleep is not important it should have died out. So if the dolphins sleep pattern has evolved to make sure it is constantly alert in its aquatic environment if it wasn't needed it would have been selected out. Nocturnal animals in the day and active at night. Others are diurnal; sleeping at night and awake in the daytime. Amt of sleep and amt of REM/NREM vary incredible.

Webb's hibernation theory- sleep is adaptive; important adaption is energy conservation (winter hibernation). Sleeping when animals can't be active saves energy (eventhough REM is quite active but overall we save energy). Evaluation of theory; Availability of food; animals sleep more when food is scarce (Berger) presumably to conserve energy. Support by small animals sleeping more than large ones; they have a relatively high basal metabolic rate; if sleep helps them to conserve energy it would make sense for them to sleep more than large animals with lower BMR's (rate they burn up energy)

Meddis safety from predation- animals sleep to keep safe from predators when active behaviour is impossible. Sleep varies with other factors. Herbivores that graze for hours have less sleep than carnivores. Animals with safe places to sleep e.g bats high up in caves can sleep in safety compared to animals like zebras, which sleep in open. Evaluation of theory. Sleep can be more risky than quiet alertness to be completely safe. Meddis's theory fails to explain why animal have 2 diff types of sleep. But supportive evidence comes from a number of studies Lesku looked at sleep patterns across 50 species abd identified; predators have more total sleep than prey; carnivores sleep longer than herbivores, animals with safe sleeping sights have more sleep; particularly REM. Correlational research; can't draw conclusions on cause & effect. Small animals may sleep for longer to conserve energy rather than for safety. Its more likely sleep patterns involve an interaction between several evolutionary and ecological factors so the approach is not reductionist; its a high-level complex view. However eventhough it has identified seperate correlations between factors and diff. types of sleep there is no clear model of why both REM & NREM has evolved. Not reductionist unlike restoration but there is more emphasis on ecological factors than physiological. It often involves observational studies; little control over extraneous variables but high ecological validity.

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Functions of sleep- restoration

Without sleep we feel tired & function less effectively; so sleep to prevent these feeling & restore physiological systems; it has a homeostatic function of maintaining a constant internal environment, so sleep restores physiological processes to their optimal level e.g body temp. The theory suggests we need some down time for maintenance and the sleep pressure we feel after increased wakefullness allows this.                                                                                                                                            Oswald- observed patients recovering from brain damage spent more time in REM. In deep NREM there was a surge of growth hormone released; essential for maintenance and repair of physiological systems. He proposed REM was a time for restoration of brain and NREM restoration of body's physiological systems. If Oswald is correct heavy exercise should lead to extended sleep to restore physiological processes. Breedlove provides evidence they fall asleep quicker but not longer; doesnt support Oswald. Oswald linked surge of growth hormone in NREM to restoration of body tissues in REM. Horne points out for growth hormone to promote tissue restoration there needs to be a supply of amino acids; part of our diet and only available for protein synethesis after eating. By the time we sleep, amino acid levels are low so its unlikely much tissue restoration could take place regardless of hormone (falsifiable- science)                                                                                                                                                                        Horne- lab based sleep deprivation studies. Assumes assessing effects of not sleeping will help us to understand normal functions of sleep. Review 50 studies and concluded; mild sleep deprivation has little/no effect; even severe deprivation didn't have dramatic consequences. Effects were on cognitive functions e.g memory. When allowed to sleep recovered far more REM and deep NREM than light NREM. Proposed core sleep was essential for maintaining brain systems which underlie cognitive processes. light NREM had no key function. He suggested sleep was not related to bodily restoration (opposing Oswald). Lab studies- under controlled conditions provide best evidence for effects of sleep deprivation. Hornes analysis demonstrates deprivation seems to affect brain and cog. functions rather than body, supports explanation that core sleep is brain restorative. These studies are low in ecological validity and there are unethical, highly stressful which makes findings unreliable

Randy Gardner - uncontrolled study compared to lab, cannot generalise findings; but useful for emphasizing individual differences in effects of sleep deprivation and speed of recovery.

Evaluation; Animal deprived studies; severe sleep deprivation in rats leads to death (Everson) supports theory. However keeping rats awake involves contant arousal and stress, and it may be the stress which is fatal; a general effect of stress is no single cause of death had been found. Would be unethical to test humans this far!

Fatal familial insomnia is a rare inherited condition; people affected sleep normally until middle age; then stop sleeping and death usually occurs within 2 years. The disorder is linked to damage in the thalamus; its likely death may be caused by thalamus rather than sleep deprivation.

Its a reductionist explanation; emphasising low-level physiological processes; ignoring ecological variables that we know influence sleep patterns e.g energy conservation.

Restoration and evolutary are not necessarily alternative; sleep may be important for maintenance of brain function, but timing and patterns of sleep may depend on evolutionary & ecological factors

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