Biological rhythms

• What are biological rhythms?

  Repeating patterns of changes that occur in over a set periods of time
• What are three types of biological rhythms?

  • Circadian rhythms
  • Ultradian rhythms
  • Infradian rhythms
• What are circadian rhythms?

  Repeated patterns of changes that occur daily, every 24 hours
• What are ultradian rhythms?

  Repeated patterns of changes that occur more than once in a 24 hour cycle (more frequent than circadian rhythms)
• What are infradian rhythms?

  Repeated patterns of changes that occur less than once in a 24 hour cycle (less frequent than circadian rhythms, often monthly / yearly)
• What is an example of circadian rhythms?

  Sleep / wake cycle - resets every 24 hours
• What are examples of ultradian rhythms?

  Sleep cycles, basic rest-activity cycle
• What are examples of infradian rhythms?

  Menstrual cycle - monthly, hibernation, season affective disorder - yearly
• What are exogenous zeitgebers?


  External cues, e.g. social cues, natural light
• What are endogenous pacemakers?

  Internal biological clocks that regulate our body, e.g. hormones, parts of the brain such as SCN, melatonin levels
• What does SCN represent?

  Suprachiasmatic nucleus
• What were three names of researchers that studied circadian rhythms?

  1. Siffre
  2. Aschoff and Wever
  3. Folkard
• How did Siffre (1962) conduct his study on circadian rhythms?

  • Spent two months underground to study the effects of his own biological rhythms
  • Deprived of exposure to natural light and sound, but had access to adequate food and drink
  • His 'free-running' biological rhythms settled down to around 25 hours (> 24 hours) though he did continue to sleep / wake on a regular schedule
• How did Aschoff and Wever (1976) conduct their study on circadian rhythms?

  • Around 10 participants spent 4 weeks in world war 2 bunkers
  • Deprived of natural light
  • All but one participant (29 hours) displayed a circadian rhythm between 24-25 hours
  • Shows that our sleep / wake cycle is entrained by exogenous zeitgebers such as daylight hours, mealtimes
• How did Folkard (1985) conduct his study on circadian rhythms?

  • 12 participants agreed to live in a dark cave for three weeks, retiring to bed when the clock said 11:45 pm and rising when it said 7:45 am
  • Over time, researchers speeded up the clock until a 24 hour day only lasted 22 hours
  • Only ONE participant was able to adjust to the new schedule
  • This suggest the existence of a strong free-running circadian rhythm controlled by endogenous pacemakers
• What is a strength of circadian rhythms research for shift workers?

  There is a better understanding of effects of desynchronisation (disruption of rhythms) in providing better support for those running shifts at night
• What are the drug treatment applications of circadian rhythms research?

  Medication can be more effective at different times (e.g. high blood pressure in the morning, high alertness in the afternoon, melatonin increase at night)
• What are some problems with using case study research for circadian rhythms?

  Generalisability? - small sample used

  Artificial light used for Siffre - inaccuracies?
• What are the weaknesses in circadian rhythms in terms of individual difference?

  Doubt on value of study as each person is entirely different, may not apply to everyone's habits (lark vs owl)
• How does the human menstrual cycle work?

  • 28 days on average
  • Controlled by internal factors -> level of oestrogen and progesterone (produce by ovaries)
  • Physiological changes -> release of egg, thickening of lining, shedding on lining
• What did McClintock (1971) find out about women's periods

  • 29 women separated into two groups
  • Sweat samples collect from 9 women's armpits (containing pheromones) and dabbed onto the upper lip of the other group fo 20 women
  • 68% of women synchronised their periods with their donors
• What exogenous zeitgebers play in the menstrual cycle?

  • Stress
  • Environmental factors
  • Lifestyle choices
• Why might there be an evolutionary advantage to menstrual synchrony?

  Women having babies at the same time could support each other taking care of the babies
• What does SAD stand for?

  Seasonal Affective Disorder
• What is SAD?

  • Type of depression that follows a seasonal pattern
  • Symptoms begin as days get shorter
  • Symptoms include low mood, lack of activity and interest
• What role does melatonin have in SAD?

  • Circadian rhythms disrupted, body overproduces an increased amount of melatonin at constant low light levels during winter
  • Melatonin is responsible for sleep regulation, produced in the pineal gland
• How can SAD be treated?

  Photo therapy - exposure to UV light
• How many stages are in the sleep cycle and how long does each stage last?

  5 stages, each 90 minutes approx.
• How was each stage of the sleep cycle identified?

  Through a different level of brainwave activity seen when using a EEG
• What waves are shown when we are awake?

  Beta waves
• What happens in stage 1-2 of the sleep cycle?

  Light sleep, easily awakened, at the beginning of sleep, brainwave patterns start to become slower and more rhythmic (alpha waves), becoming even slower as sleep becomes deeper (theta waves)
• What happens in stage 3-4 of the sleep cycle?

  Delta waves, slower and have a greater amplitude than earlier wave patterns, deep sleep / slow wave sleep, difficult to wake someone at this point
• What happens at stage 5 of the sleep cycle?

  REM sleep (rapid eye movement), body is paralysed yet brain activity speeds up significantly to the same speed as the awake brain, dreaming sleep
• What is the suprachiasmatic nucleus?

  Tiny bundle of nerve cells located in the hypothalamus in each hemisphere, it is one of the primary endogenous pacemakers in mammals, regulates the body's circadian rhythm
• How does the suprachiasmatic nucleus work?

  Nerve fibres connected to eye cross in an area called the optic chiasm on their way to visual area of the cerebal cortex, the SCN lies just above the optic chiasm, which receives information about light directly from this structure. This continues even when our eyes are closed, enabling the biological closk to adjust to changes patterns of daylight whilst we are asleep.
• What were some animal studies conducted to research the SCN?

  DeCoursey (2000) - destroyed SCN connections in the brain of 30 chipmunks who were then returned to their natural habitat for 80 days, significant amount of them were killed by predators because their sleep/wake cycle disappeared

  Ralph (1990) - bred 'mutant' hamsters with a 20 hour sleep/wake cycle, their SCN cells from the foetal tissue of mutant hamster were transplanted into the brains of normal hamsters, the second group's cycle shifted to 20 hours

  • Both studies emphasise the role of the SCN in establishing and maintaining circadian sleep/wake cycle
• What are two main endogenous pacemakers?

  The SCN and pineal gland
• What does the pineal gland produce?

  Melatonin
• How does the SCN work together with the pineal gland?

  SCN passes information on day length and light to the pineal gland, during the night the pineal gland increases production of melatonin

  • Low levels of light (retina) -> melanopsin carries signals to SCN -> axon pathway to pineal gland -> melatonin -> induced sleep
• Where is the pineal gland?

  Just being the hypothalamus