biological rhythms

• how long do circadian rhythms last?

  24 hours
• define circadian rhythms

  regulated by internal biological clocks and external cues
• example of circadian rhythms

  sleep/wake cycle
• 💤 outline the sleep/wake cycle as a circadian rhythm

  • controlled by endogenous pacemakers and exogenous zeitgebers
  • daylight activates the retina which sends message to the SCN
  • SCN signals the pineal gland to reduce melatonin
  • darkness triggers increased melatonin
• key research into circadian rhythms

  siffre
• 📖 siffre's cave study of circadian rhythm

  • 6 months in a cave without natural light or clocks
  • sleep/wake cycle settled at 25 hours
  • internal biological clock persists without external cues
• how long do infradian rhythms last?

  longer than 24 hours
• examples of infradian rhythms

  • menstrual cycle
  • seasonal affective disorder
• 🤦🏼‍♀️ outline menstrual cycle as an infradian rhythm

  • lasts 28 days
  • controlled by oestrogen and progesterone
• 😓 outline seasonal affective disorder as infradian rhythm

  • type of depression linked to seasons
  • lack of light leads to higher melatonin
  • disrupts rhythms and affects serotonin production
• key research into infradian rhythms

  McClintock & Stern
• 📖 McClintock & Stern's study into infradian rhythm

  • 29 women with irregular periods
  • collected pheromones from 9 women
  • pheromones applied to other women's upper lips
  • menstrual cycles synchronised
• how long do ultradian rhythms last?

  less than 24 hours
• example of ultradian rhythms

  sleep stages
• 🛌 outline sleep stages as an example of an ultradian rhythm

  • lasts 90 minutes that's repeated throughout the night

  stage 1 & 2 - light sleep with slow brain waves

  stage 3 & 4 - deep sleep which is important for physical repair

  stage 5 - rapid eye movement where dreaming occurs
• key research into ultradian rhythms

  dement & kleitman
• 📖 dement & kleitman's study into ultradian rhythms

  • monitored brain activity during sleep using an EEG
  • found clear patterns in sleep stages
  • waking participants during REM led to vivid dream recall
• define endogenous pacemaker

  internal body clocks
• ⏰ main biological clock

  suprachiasmatic nucleus

  • tiny bundle of nerves in the hypothalamus
• function of the SCN

  • receives light input via the optic nerve
  • controls release of melatonin by the pineal gland
• key study into endogenous pacemakers

  morgan
• 📖 morgan's study into endogenous pacemakers

  • removed SCN in hamsters
  • transplanted SCN from mutant hamsters
  • adopted a 20 hour cycle
• define exogenous zeitgeber

  external cues
• 2 main exogenous zeitgebers

  1. light
  2. social cues
• key study into exogenous zeitgebers

  campbell & murphy
• 📖 campbell & murphy's study into exogenous zeitgebers

  • shone light onto back of knees
  • cycles shifted
  • light can affect rhythms without eye detection
  • multiple pathways for entrainment
• ✅ circadian rhythms

  scientific studies

  • Siffre - lived in a cave with no natural light and found cycle settled to 25 hours
  • endogenous pacemakers operates in absence of external cues
  • demonstrates consistency
• ❌ circadian rhythms

  small, unrepresentative samples

  • Siffre - rhythm slowed with age
  • individual difference
  • limited external validity
• ✅ circadian rhythms

  real-world applications

  • shift workers have reduced alertness during circadian troughs
  • enhance productivity, health and safety
• ✅ infradian rhythms

  adaptive social benefits

  • McClintock & Stern - pheromones from women at different menstrual stages could synchronise cycles
  • exogenous factors can influence rhythms
• ❌ infradian rhythms

  poor control and inconsistent findings

  • diet, stress and exercise influence menstruation
  • failure to replicate McClintock's study weakens reliability
  • confounding variables limits internal validity
• ✅ infradian rhythms

  treatment for SAD

  • disrupted melatonin and serotonin production during winter
  • Eastman et al - phototherapy is effective for 60% of patients
  • valuable medical applications
• ✅ ultradian rhythms

  objective methods

  • Dement & Kleitman - used EEG recordings
  • provide real-time measurement
  • increases internal validity and replicability
• ✅ ultradian rhythms

  real-world relevance

  • research into BRAC suggests people are most alert for 90 minutes before needing a break
  • recognising REM and sleep stages help diagnose and treat sleep disorders
  • improve mental health and workplace efficiency
• ❌ ultradian rhythms

  sleep cycle research varies

  • factors such as age, lifestyle, medication and genetics
  • findings are not universal
  • lack population validity
• ✅ EP & EZ

  animal research

  • Morgan - transplanting SCN from hamsters with a 20 hour rhythm caused recipients to adopt cycle
  • SCN is master biological clock for regulating rhythms
  • strong biological support
• ❌ EP & EZ

  lacks application to humans

  • influenced by more complex social, cognitive and environmental factors
  • e.g. work patterns, culture and artificial light
  • limited generalisability
• ✅ EP & EZ

  light can reset biological rhythms

  • campbell & murphy - shining light on the back of knees could shift sleep/wake cycle
  • light is a zeitgeber that influences rhythms independently
  • supports interactionist view