Unit 3: Biological rhythms and sleep
Exam board specification:
Biological rhythms /- Circadian, infradian, and ultradianrhthyms, including the role of endogenous pacemakers and of exogenous zeitgebers in the control of circadian rhythms
- Disruption of biological rhythms, for example shift work, jet lag
Sleep /
- The nature of sleep including stages of sleep and lifespan changes in sleep
- Functions of sleep, including evolutionary and restoration explanations
Sleep disorders /
- Explanations for sleep disorders, including insomnia, sleep walking and narcolepsy
What you need to know:
You will be expected to outline and evaluate each of the areas.
Circadian rhythms: / -The sleep-wake cycle, including the role of enodogenous pacemakers and endogenous zeitgebers in this rhythm.Disruption of the biological rhythms: / -How circadian rhythms are affected by shift work and jet lag.
Infradian rhythms: / -The menstrual cycle.
Ultradian rhythms: / -The sleep cycle.
Nature of sleep: / -The sleep stages
-The changes in sleep patterns throughout a person’s life.
Functions of sleep: / -Evolutionary: Webb & Meddis
-Restoration: Horne & Oswald
Explanations for sleep disorders, including insomnia, sleep walking and narcolepsy: / -Primary Insomnia: Predisposing, precipitating and perpetuating factors
-Sleep walking: Diathesis-stress model
-Narcolepsy: The role of hypocretin
Key terms/concepts
Where possible, include examples in order to help your understanding (see example)
Circadian rhythms / These are rhythms that last 24 hours. E.G. the sleep-wake cycle.Our bodies have many other circadian rhythms, such as temperature regulation and bowel regulation.
Endogenous pacemakers
Exogenous zeitgebers
Suprachiasmatic nucleus (SCN)
Melotonin
Jet lag
Phase delay
Phase advance
Social jet lag
Shift work
Infradian rhythms
Follicle stimulating hormone
Oestrogen
Luteinizing hormone
Progesterone
HCG
Pheromones
Ultradian rhythms
REM sleep
EEG’s
EOG’s
EMG’s
Here are a few extra boxes if you come across any additional terms:
Biological rhythms
Circadian rhythms
Circadian rhythms are biological rhythms that last about 24 hours, that is, one day in length. One example is the sleep-wake cycle. This cycle is controlled by endogenous pacemakers acting as internal body clocks that elicit internal biological changes such as the secretion or inhibition of hormones, and exogenous zeitgebers that serve to entrain our biological clocks.
An example of an endogenous pacemaker is the suprachiasmatic nucleus (SCN) which has neural connections with the pineal gland, responsible for producing melatonin. An increased production of melatonin leads to increased tiredness.
There are many exogenous zeitgebers, one being light. The retina has photosensitive cells that send signals to the optic chiasm which in turn stimulates the SCN. When it is lighter, the SCN tells the pineal gland to produce less melatonin thus making us feel more awake. In this sense, internal and external pacemakers work together to control our sleep-wake circadian rhythm.
It is thought that out natural, innate clock runs just over 24 hours.
Another example is body temperature, which is regulated by an endogenous pacemaker in the suprachiasmatic nucleus. Core body temperature changes by about 1 degree Celsius. Temperature is higher in the afternoon than in the morning. During a night’s sleep, core body temperature declines gradually. The rhythm is associated with the circadian rhythm of the sleep-wake cycle. We feel sleepier when the body temperature is low.
Evaluation of circadian rhythms - the sleep-wake cycle
Research evidence:
Morgan (1995) used hamsters with abnormal circadian rhythms (20 hrs rhythm rather than 24) and transplanted SCN neurons from these hamsters into normal hamsters (24hr rhythm). They found that the normal hamster’s circadian rhythmschanged from 24hrs to 20. They also did this experiment in reverse by transplanting the SCN neurons from the normal hamsters to the abnormal hamsters and found their circadian rhythm changed from 20hrs to 24.
How does this evidence relate to the role of endogenous pacemakers and/or exogenous zeitgebers?Schochat et al (1997) studied the role of melatonin in circadian rhythms. Six male participants spent 29 consecutive hours (from 7 am one day to noon the next) in a sleep laboratory. They had to spend 7 minutes in every 20 minutes lying down in a dark room trying to sleep. The researchers were looking at how easy/hard the participants found it to go to sleep; the period that is the easiest for people to go to sleep in is known as the sleep gate. Blood samples were also taken every 20 minutes to allow the measurement of melatonin. The researchers found that the daily secretion (release) of melatonin into the blood consistently preceded the sleep gate by 100-120 minutes. Other researchers have also found that people who suffer from insomnia (sleeplessness) found it much easier to get to sleep when they were given melatonin about 2 hours before bedtime.
How does this evidence relate to the role of endogenous pacemakers and/or exogenous zeitgebers?Michel Siffre spent 2 months living in a dark cave. He developed a 25 hour sleep wake cycle when it is normally 24 hours. Miles et al (1977) wrote about a man who was blind from birth. He had a 24.9 hours circadian rhythm despite the fact that he was exposed to external cues such as radios and clocks. The only way he could reset his circadian rhythm to 24 hours was through the use of sedatives to help him sleep and stimulants to help him wake.
How does this evidence relate to the role of endogenous pacemakers and/or exogenous zeitgebers?Mariana Figeuiro (2012) set out to determine what the effects of self-luminous tablets (Ipads) might be on melatonin suppression. They observed and gathered data on 13 volunteers who used the devices to watch films, play games and read documents. They found that a two-hour exposure to light from self-luminous electronic displays can suppress melatonin by about 22 percent. Stimulating the human circadian system to this level may affect sleep in those using the devices prior to bedtime.
How does this evidence relate to the role of endogenous pacemakers and/or exogenous zeitgebers?IDA:
Choose one IDA point and write a comment on how the point relates to this topic and why this is an important point.Wider evaluation points:
Individual differences:
- Czeisleret al (1999) found that circadian cyclesin different people can vary from 13 to 65 hours.
- Cycle onset varies, Duffy et al. (2000) found that morning people preferto rise early and go to bed early (about 6.00 am and 10.00 pm), whereasevening people prefer to wake and go to bed later (10.00 am and 1.00 am).
Usefulness/Practical applications:
- Implications surrounding use of self-luminous tablets.
- Chronotherapeuticsis the study of how timing (chronos) affects drug treatments (therapy).Since the circadian rhythm affects digestion, heart rate, hormone secretions and other functions, this should be taken into account when taking drugs. For example, medications that act on certain hormones may have no effect if taken when target hormone levels are low but are fully effective if taken when levels are high.
- Another application of this research is when deciding on the best time to study. You are most alert in the morning and early evening, so those are the best times to work.
Ultradian rhythms
Ultradian rhythms are rhythms that last less than a day such as the sleep cycle.
There are two main phases of sleep which make up the rhythm; REM (rapid eye movement) and NREM (non-rapid eye movement). These can be observed on an electroencephalogram (EEG).
NREM sleep has 4 stages, stage 1 and 2 are known as the lighter stages of sleep and stage 3 and 4 are known as slow wave sleep (SWS). Most people have five cycles of sleep that last approximately 90 minutes. Deep sleep, or slow-wave sleep (SWS), occurs in only the first two cycles; REM sleep occurs in all of the cycles, and increases during the course of the night’s sleep.
- First cycle: Go down the sleep staircase from stage 1 to 4; then ascend through stage 3 and then stage 2. Stage 5, or REM sleep, follows this and lasts for approximately 10 minutes.
- Second cycle: Begin at stage 2, which lasts for about 20 minutes, then descend through stage 3 to the deep sleep of stage 4, which lasts approximately 30 minutes. Then ascend through stages 3 and 2. REM sleep (stage 5) completes the cycle and again lasts for about 10 minutes.
- Third cycle: Enter at stage 2 and spend about an hour in this stage. Next we miss the descent of the sleep staircase by going straight into REM sleep (stage 5) for approximately 40 minutes.
- Fourth cycle: Enter at stage 2 for 70 minutes and then enter REM sleep (stage 5) for approximately an hour.
- Fifth cycle: Enter at stage 2 followed by REM sleep (stage 5). This is known as the emergent cycle because we may wake from either stage. We are more likely to remember our dream if we wake in stage 5 and can experience a hypnogogic state again and so recall vivid visual images as we wake.
Another example of an ultradian rhythm is the levels of alertness throughout the day. Studies have shown that we have stages of alertness throughout the day. A study of pupillary size showed that these rhythms can last around 75-125 minutes and could be dependent on melatonin levels or central nervous system arousal. Studies have generally shown that humans tend to be most alert at two separate times in the day, in the morning just after waking up, and at around 7-8 pm.
Evaluation of ultradian rhythms – the sleep cycle
Research evidence:
There is much evidence concerning the ultradian rhythm – the main body of research has been carried out in sleep labs using specialized equipment which the sleeper is wired up to:
- Electroencephalographs (EEGs) measure electrical activity (brain waves)
- Electro-oculograms (EOGs) measure eye movements
- Electromyograms (EMGs) measure muscle movement
This equipment has allowed researchers to distinguish the stages of sleep and to identify the cycles of sleep.
Dement and Kleitman (1957)studied 9 participants in a sleep lab using the equipment mentioned above. They found that the participants all showed similar rhythms whilst sleeping which alternated between NREM and REM. REM lasted from 3 to 50 minutes and the REM periods occurred at regular intervals during the night. The mean period between each REM phase for the whole group was 92 minutes, with individual norms varying between 70 minutes and 104 minutes.
How does this evidence demonstrate ultradian rhythms?Wehr (1992) conducted a study in which participants (young adults) were plunged into darkness for 14 hours per day. Whilst it took some time for their sleep to regulate, by the fourth week the participants settled into a regular pattern: they slept first for three to five hours, and then woke for one or two hours before falling into a second three to five hour sleep.
Ekirch (2001) has carried out much research into the historical record across cultures, and has found substantial evidence for the segmented sleep pattern observed by Wehr, although in western society the idea of a first and second sleep had vanished by 1920. It seems that as the night has become more of a time for social activity, the length of time that people wish to spend on rest has reduced, so the gap between the first and second sleep becomes a waste of time and people now attempt to sleep in one eight hour segment.
What does this research suggest about biological rhythms?IDA:
Choose one IDA point and write a comment on how the point relates to this topic and why this is an important point.Wider evaluation:
Individual differences:
How does Dement and Kleitman’s study demonstrate individual differences in the sleep cycle?
In what way do ultradian rhythms differ with age? (you may need to look at the ‘lifespan changes in sleep’ section)
Infradian rhythms
Infradian rhythms are biological rhythms that last longer than a day. An example would be the menstrual cycle, which on average is 28 days. It is controlled endogenously by hormones such as oestrogen, follicle stimulating hormone (FSH) and luteinising hormone (LH). The pituitary gland produces FSH which starts the development of one egg in a follicle in one of the ovaries stimulating the ovaries to produce oestrogen. This stimulates the pituitary gland to secrete LH which causes ovulation and stimulates the empty follicle to produce progesterone. Progesterone causes the lining of the uterus to get thicker ready for the fertilised egg. If the egg is not fertilised, production of oestrogen and progesterone stops, the lining of the uterus breaks down and menstruation occurs.
It is now thought by some researchers that the occurrence of any single menstrual cycle could be influenced by prolonged exposure to other women who release pheromonesduring menses causing inter-woman menstrual synchronisation.Pheromones are biochemicals, like hormones and neurotransmitters, but instead of being transmitted through the blood or brain cells, they are released into the air, and affect other individuals. In humans, they can be released in sweat.
Another example is seasonal affective disorder. Sufferers of SAD feel depressed in the winter months. The cycle occurs annually. The longer nights in winter mean that we experience longer periods of darkness. Melatonin is produced in dark conditions and has been associated with depression.
Evaluation of infradian rhythms – the menstrual cycle
Research evidence:
Russell et al (1980) arranged to apply the pheromones of one woman to a group of sexually inactive women. The donor’s odour was collected from pads placed under her arms. Once every 24 hours the pads were replaced. The old pad was then dissolved in alcohol to remove any bacteria. Finally, the pad was rubbed on the upper lip of each participant. This was repeated daily for 5 months. Some of the women were in a control group where they received the same treatment but did not receive the odour. Participants did not know which group they were in. A record was kept of the participants’ menstrual cycles. At the end of the experiment, four out of five women in the odour group had menstrual cycles that synchronised to within a day of the odour donor.
McClintock (1971) suggested that male pheromones may reset a woman’s biological clock. This comes from the observation that women who work with men often experience a shortening of their menstrual cycle. This would be an evolutionary advantage because females who reproduce more often will have more offspring and therefore their genetic line is likely to become dominant
How does the evidence above demonstrate the role of exogenous zeitgebers in this rhythm?Reinerg (1967) documented the case of a woman who spent 3 months in a cave with only dim lighting and found that her menstrual cycle became shorter (25.7 days)
How does this evidence demonstrate the role of endogenous pacemakers in this rhythm?IDA:
Choose one IDA point and write a comment on how the point relates to this topic and why this is an important point.Wider evaluation points:
Disruption of biological rhythms: jet lag and shift work
You are going to look at how circadian rhythms, in particular, are disrupted by jet lag and shift work.
Jet lag
Jet lag occurs when normal circadian rhythms are disrupted by travelling across time zones. When an individual travels across time zones there is a shift in zeitgebers, which causes a temporary mismatch between our internal circadian clock and external cues (e.g. light and time). Therefore disruption occurs when there is sufficient discrepancy between internal time (your biological clock, which is set to British time) and external time (local time of destination).
Travelling from east to west leads to phase delay of the body clock, which seems easier for the body to cope with than phase advance. Phase delay simply means extending the duration of a rhythm’s cycle (e.g. from 24 hours to 29 hours before returning to 24 hours again), whereas phase advance means shortening the rhythm’s cycle.
Typical effects of jet lag include: disturbed sleep, impaired functioning and decreased alertness.
Research on jet lag:
Schwartz et al (1995) analysed the results of American baseball games where teams had to travel across time zones to play opposing teams on the east or west coast, causing a time difference of three hours. West coast teams who travelled east had significantly fewer wins than the east coast teams who travelled west.