Biological rhythms

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What is a circadian rhythm?
Rhythms that last about 24 hours
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What are types of circadian rhythm?
Core body temperature, Sleep wake cycle and Hormones
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When is core body temperature at its lowest?
At around 4:30am at 36 degrees
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When is core body temperature at its highest?
At around 6pm at 38 degrees
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How are circadian rhythms synchronised?
By exogenous zietgabers such as light or meal times
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What are studies that support endogenous pacemakers?
Siffre and Miles
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What did Miles find?
Found blind people show the same pattern as sighted people, suggests although external factors may be important there are also endogenous pacemakers
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What is the main endogenous pacemaker?
The Suprachiasmatic Nucleus (SCN)
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What is the role of the Suprachiasmatic nucleus cycle?
Light enters the eye, info sent via neural pathway to SCN, info then sent via another neural pathway to pienal gland, low light info from SCN then triggers pienal to release melatonin, melatonin reaches critical level = sleep
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Where is the SCN located?
The hypothalamus
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Where is the pienal gland located?
Deep within the brain
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When can the circadian cycle disappear?
When the SCN is destroyed
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What is Cortisol?
A hormone produced when stressed and is related to making us alert often when we wake up
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When is Cortisol high and low?
At its lowest at around 12am and peak at about 6am
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What is Chronotherapeautics?
Study on how timing affects drug treatment, Circadian rhythms affect digestion, heart rate, hormone secretions and other functions, medications acting on hormones may not have an effect if taken when hormones are low and fully effective when high
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When is the best time to treat heart attacks?
Normally occur in early morning, most effective to take mediaction at 11pm which allows aspirin to peak in the blood stream
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How is circadian rhythms deterministic?
Suggests the sleep wake cycle patterns are fixed and determined by internal mechanisms
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What are infradian rhythms?
Cycles which last longer than 24 hours
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What are examples of infradian rhythms?
Menstruation and Seasonal Affective Disorder (SAD)
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How is the menstrual cycle controlled?
Generated by hypothalamus, fluctuations in hormone levels, controlled by hormones such as progesterone and oestrogen which regulate ovulation
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What is SAD?
Depressed in winter and recover in summer
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What did research finds happen during SAD?
Hormones melatonin and serotonin are secreted when dark, more darkness means more melatonin and less serotonin, low levels of serotonin are correlated with depression
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What are ultradian rhythms?
Rhythms completed more than once every 24 hours
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What happens in stage 1 of sleep?
BRain waves relax to alpha rhythms, reduces heart rate, muscle tension and temperature
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What happens in stage 2 of sleep?
EEG becomes larger and slower and move into feta waves. K complexes are the brains response to external factors, lasts 20 mins but easily wakened
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What happens in stage 3 of sleep?
EEG consists of long, slow large delta waves as sleep deepens, snoring and deep breathing occur
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What happens in stage 4 of sleep?
Slow wave sleep (SWS) deepens, hard to wake someone, body temp drops and sleep walking and talking occurs
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What happens in stage 5 of sleep?
Rapid Eye Movement (REM), even harder to waken someone in this stage, brain is very active but body is paralysed preventing us from acting out our dreams
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What happens to our biological rhythms during shift work?
Reverse our biological rhythms and are out of line from zietgabers
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How does decreased alertness effect night workers?
They often experience a circadian 'trough' of decreased alertness during shifts, occurs between midnight when cortisol levels are lowest and 4am when core body temp lowest
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Why can sleep deprivation effect shift workers?
They sleep in the day and there are distruptions outside such as noises and daylight, which reduces the quality of our sleep, REM is mainly effected, the poor quality sleep makes it harder to stay awake at night
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What is the effect of shift work on health?
There is a relationship between shift work and organ disease. Knutsson et al found people working shifts for 15 years were 3 x more likely to develop heart disease
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How does jet lag effect our biological rhythms?
Causes physiological effects of disrupted circadian rhythms, our biological rhythms are not equipped to cope with sudden changes
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What is the effect of jet lag on the SCN?
Dorsal portion of the SCN takes several cycles to fully resynchronise to large changes, Winter found it is equivalent to one day to adjust to each hour of time changed
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What are symptoms of jet lag?
Loss of appetite, nausea, fatigue, disorientation, insomnia and mild depression
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How does jet lag effect performance?
The west coast of America is 3 hours behind East coast, when east coast teams play on west coast they experienced clocks going back
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What did Recht et al find about jet lag and performance?
Analysed US basket ball reulsts over 3 years, teams travelling east to west won 44% of games and west to east won 37%
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What is the nature of sleep for infancy?
Babies have a lot of sleep compared to adults, tend to sleep 16 hours, sleep cycles shorter so wake up every hour or so, active and quiet sleep, 1/2 sleep in active, by 6 month develop CR, by 1 sleep mainly at night and 1/2 naps & REM reduces
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What is the nature of sleep for childhood?
By 5 children have EEG patterns which looks like adults but still sleep more at around 12 hours, have more REM activity at around 30%, boys sleep slightly more than girls, it is common to experience parasomnias such as sleep walking and night terrors
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What is the nature of adolescence sleep?
Need for sleep decrease to about 9 or 10 hours, circadian rhythms change so teenagers feel naturally more awake later at night and difficulty waking early,
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What is the nature of adulthood and old age?
Normally 8 hours per night with 25% REM, parasomnias are more rare, increasing frequency of disorders like insomnia,
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What is the nature of sleep for old people?
More difficulty sleeping and wake up more frequent, may need naps during, REM decreases to 20% and SWS as low as 5%, may also experience phase advance of CR and feel sleepier in evening & wake up earlier
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What is the restoration theory?
Suggests we sleep because we need time during sleep to restore both our mind and body through SWS and REM
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How does Slow Wave Sleep (SWS) restore the body?
A growth hormone is secreted, which stimulates growth which is important in childhood, in adulthood it enables protein synthesis and cell growth which is significant at night
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Why is protein synthesis and cell growth important?
Restores body tissue which are fragile and need to be constantly renewed
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What did Sassin et al find?
When the sleep wake cycle is reversed by 12 hours, by going to sleep in morning and get up at night, release of GH is reversed, showing GH is controlled by neural mechanism related to SWS
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How does sleep affect the immune system?
Lack of SWS associated with reduced functioning of the immune system, the body's system of defence against viruses and bacteria, the immune system consists of various protein molecules regenerated during cell growth and protein synthesis
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How does REM sleep restore the body?
Active/REM is more active in babies than adults, more in premature babies because they have rapid brain growth
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What did Siegle state?
Amount of REM in any specy is dues to the immaturity at birth, such as the platypus and have about 8 hours of REM, where as dolphins have almost no REM and can swim from birth, suggesting relationship between neural development and REM sleep
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How does REM effect memory?
Crick & Mitchinson- proposed during REM, unwanted memories are discarded and make more memories accessible & Stickgold- REM may be more important in consolidating procedual memore (Skills eg ride bike) and SWS more important for sematic & episodic
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What is foraging requirements?
Time spent sleeping may be constrained by food requirements as an animal has to gather food, berivores cant afford to spend time sleeping as they need to spend a long time gathering food, carnivores eat food rich in nutrients
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What is predator avoidance?
If an animal is a predator it can sleep for longer, prey species sleep is reduced as they need to remain vigalent to avoid predators, if sleep is vital they're best to sleep when least vulnerable, predators sleep longer
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What is the Meddis' safety hypothesis?
He suggested sleep helps animals to stay out of the way of predators during parts of the day when most vulnerable eq hours of darkness for many animals, slee in well hidden places and ensure stay still when nothing to do
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What is Sigel's safety hypothesis?
Being awake is riskier than sleeping becuase animals are likely to get injured eq the little brown bat is awake for a few hours each day, only when insects are awak to eat
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What is energy conservation?
Warm blooded animals need to expend a lot of energy to maintain a constant body temp, problem for small animals with high metabollic rates. All activities use energy, animals with a high metabollic rate use even more. Sleep provides inactivity
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What is insomnia?
The issue of getting to sleep or staying asleep
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What are clinical characteristics of insomnia?
Difficulty initiating or maintaining sleep for at least one month, Sleep disturbance or related to sleep time fatigue causes significant distress or impairment in functioning
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What is primary insomnia associated with?
Not any other mental or medical condition or drug use
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What is secondary insomnia ssociated with?
A mental disorder, usually depression or a medical condition or drug use
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What are type of primary insomnia?
Learned insomnia, Sleep state misperception, Idiopathic insomnia
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What are types of secondary insomnia?
Environmental factors, poor sleep hygiene, circadian rhythm distruption, medical condition
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What is narcolepsy?
Where an individual experiences sudden and uncontrollable attack of sleep at irregular times which may last seconds or minutes, often triggered by stressful situations
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What is the REM explanation of narcolepsy?
A symptom is loss of muscle tone (cataplexy), similar to REM sleep, they often experience intrusions of REM sleep (hallucinations), at night they have an abdomnal REM sleep they go straight into REM
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What is the hypocretin explanation of narcolepsy?
It is a neurotransmitter to regulate sleep and wakefulness through interactions with systems which regulate emotion and homeostasis in the hypothalamus, there is normally 10,000 to 20,000 producing in hypothalamus, but a lot less
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When does sleep walking occur?`
Stage 4, SWS sleep
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What is sleep walking?
A range of activities which take place whilst sleeping but normally associated with wakefulness eq walking, eating and dressing and person has no knowledge of what they're doing
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How is sleep walking cause by incomplete arousal?
They are partly awake in sense that they're engaged in activities associated with awake state, recordings found mix of delta(SWS) and high frequency belta waves(awake state), hence looks like occurs in deep sleep but rousal of brain isn't complete
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What are risk factors associated with sleep walking?
sleep deprivation, alcohol,fever, stress, hormonal change in puberty and menstruation
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Why may their be an inherited vulnerability to sleep walking?
Because in some people certain risk factors are triggered suggesting some individs may have inherited it
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Why are children more vulnerable to sleep walking?
Children have more SWS than adults, Oliviero suggested the system which normally inhibits motor activity in SWS isn't fully developed in some children and some underdeveloped adults
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What are types of circadian rhythm?


Core body temperature, Sleep wake cycle and Hormones

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When is core body temperature at its lowest?


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When is core body temperature at its highest?


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How are circadian rhythms synchronised?


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