biological rhythms

• biological rhythms

  repeating patterns of changes that occur over a set period of time

  • circadian - daily (sleep cycle)
  • ultradian - more than once in 24 hours (stages of sleep cycle)
  • infradian - less than once in 24 hours (menstrual cycle)
• circadian rhythms

  biological rhythms subject to a 24 hour cycle, which regulate a number of body processes such as the sleep / wake cycle and changes in body temperature
• endogenous pacemakers

  the bodys internal biological 'clocks'
• exogenous zeitgebers

  external changes in the environment
• the sleep / wake cycle

  • exogenous zeitgeber - effect of daylight (alert when daytime / drowsy when nighttime)
  • endogenous pacemaker - cycle governed by suprachiasmatic nucleus (SCN)
  • SCN lies above optic chiasm, provides information from the eye about light
  • light (EZ) can reset the SCN
  • what were to happen if the biological clock was left to its own devices without influence of external stimuli?
• siffre - cave study

  • spent extended periods underground to study effects of his own biological rhythms
  • deprived of natural light and sound but had access to food and drink
  • spent 2 months in caves - resurfaced thinking it was september when it was august
  • 10 years later spent 6 months in a cave
  • in both cases his 'free running' biological rhythm settled to one around 25 hours, though did continue to fall asleep and wake up on a regular schedule
• aschoff and wever - bunker study

  • convinced gorup of Ps to spend 4 weeks in a WW2 bunker deprived of natural light
  • all but one of the Ps (whose sleep / wake cycle extended to 29 hours) displayed circadian rhythms between 24 and 25 hours
  • suggests the natural sleep / wake cycle may be slightly longer than 24 hours but is entrained by EZs associated within our 24 hour days (like typical mealtimes, number of daylight hours)
• folkard - dark cave study

  • group of 12 Ps living in a dark cave for 3 weeks
  • went to bed when the clock said 11.45 pm and woke up when it said 7.45 am
  • unbeknown to Ps, researchers gradually sped up the clock so an apparent 24 hour day only lasted 22 hours
  • revealed only 1 P could comfortably adjust
  • suggests existance of strong free running circadian rhythm that cannot be easily overridden by EZs
• circadian rhythms eval - :) practical application for shift workers

  • provides understanding for adverse consequences when interrupted (desynchronisation)
  • night workers in shift work have reduced concentration around 6 am (circaian trough), meaning mistakes and accidents are more likely
  • shift workers are 3x more likely to develop heart disease than those who work normal shift patterns
  • shows research into the sleep / wake cycle may have real world economic implications in terms of how to best manage worker productivity
• circadian rhythms eval - :( counterpoint against shift workers - correlational methods used

  • difficult to establish whether desynchronisation is actually a cause of negative effects, may be other factors
  • high divorce rates in shift workers may be due to strain of deprived sleep / missing out on important family events
  • suggests may not be biological factors creating adverse consequences associated with shift work
• circadian rhythms eval - :) has been used to improve medical treatments

  • CRs coordinate a number of basic processes like heart rate, digestion and hormones
  • these rise and fall during the course of a day which has lead to chronotherapeutics (how medical treatment can be administered in a way coordinating to a persons biological rhythm)
  • eg. asprin is most effective for heart attacks if taken last thing at night
  • reduces blood platelet activity which can reduce risk of heart attacks (they are more likely to happen in the morning - timing matters)
  • shows research can help improve effectiveness
• circadian rhythms eval - :( individual differences - generalisations are difficult to make

  • studys are based on very small samples of Ps (just 1 in siffre) and it seems sleep / wake cycles vary from person to person (from 13-65 hours)
  • study shows some people have a natural preference for going to sleep / rising early and some prefer the opposite (larks vs owls)
  • even siffre in a later study observed his own cycle had slowed down since he was young
  • means its difficult to use the research data to discuss anything more than averages, which may be meaningless
• infradian rhythms

  monthly or yearly cycles, occur less than once within a 24 hour period
• infradian rhythms - human menstrual cycle

  • outline - controlled by levels of progesterone and oestrogen (endogenous pacemakers), cause release of 1 egg from the ovaries and thickening of uterus lining which sheds if the egg isnt fertilised and menstruation occurs
  • exogenous zeitgebers - role of pheromones, mcclintock - 29 women with irregular cycles. sweat samples of 9 collected and put on lip of other 20. 68% recipients cycles alters and synced with others
  • menstrual synchrony advantage - women having babies at same time can support eachother
• infradian rhythms - SAD

  • outline - seasonal affective disorder, winter depression that starts as days get shorter
  • role of melatonin - low light levels stimulate more melatonin which causes SAD
  • how it can be treated - phototherapy, exposure to UV light
• ultradian rhythms - the sleep cycle

  5 stages of sleep, 90 minute spans, different levels of brain activity which can be monitored using EEG

  • stages 1 and 2 - light sleep where person can be easily woken. at beginning of sleep wave patterns become slower + more rhythmic (alpha waves) becoming slower as sleep gets deeper (theta waves)
  • stages 3 and 4 - even slower waves with greater amplitude (delta waves), deep sleep, difficult to rouse someone
  • stage 5 - REM sleep, body is paralysed yet activity speeds up in a manner like the awake brain, rapid eye movement, dreaming
• the suprachiasmatic nucleus (SCN)

  • bundle of nerves on hypothalamus
  • influences sleep / wake cycle as well as other circadian rhythms
  • gets info from optic chiasm about light / dark so the biological clock can adjust to changing patterns of daylight
  • of the humans primary endogenous pacemakers
• animal studies and the SCN

  • decoursey - destroyed SCN connections in brains of 30 chipmunks who were put back in their habitat and observed. their sleep / wake cycle disappeared and by the end a lot of them had been killed by predators (awake and vulnerable to attack - should have been asleep)
  • ralph - mutant hamsters with 20 hour sleep / wake cycle, SCN cells from them were transplanted into normal hamsters and then the cycles of this group defaulted to 20 hours also
  • both emphasise role of SCN in establishing / maintaining the sleep / wake cycle
• pineal gland

  • located just behind hypothalamus, receives info on day length and light
  • during night releases melatonin (sleep inducing chemical) and is inhibited during periods of wakefulness
  • suggested as a casual factor in SAD
  • sensitivity of pineal gland and SCN to light means although they are endogneous pacemakers their activity MUST be synchronised with the light and darkof environment. therefore, desynchronisation is a problem
• exogenous zeitgebers - light

  • environmental events responsible for resetting biological clock
  • can include social cues - meal times, social activities (humans can compensate for lack of light by using these instead) but light is the main one
  • resets the body clock each day, keeping the 24 hr cycle
  • SCN contains receptors sensitive to light and this external cue is used to synchronise the bodys internal organs and glands
  • melanopsin (protein in eye) is sensitive to light and carries signals to eye to reset the 24 cycle
• endogenous zeitgeber eval

  • siffre - shows internal body clock (SCN) runs without any external cues as he kept his sleep/ wake cycle. BUT he did end up with a 25 hr cycle which shows light is needed each day to reset us to 24 hrs
  • miles - blind man, 25 hour cycle and despite exposure to social cues it couldnt be adjusted. didnt receive info about light levels, shows light is crucial in synchronising the internal body clock (SCN)
  • overall... cant study 1 factor without the other as EP and EZs are constantly interacting - too simplistic (even siffre had light from lamp and meal times). all ignore individual differences (larks v owls)