circadian rhythms, endo/exo

• what are circadian rhythms

  the 24 hour cycles of sleep and wakefulness
• what is the internal biological clock called


  the suprachiasmatic nucleus (SCN)
• where is the SCN located 


  in the hypothalamus just above the pineal gland
• how does the SCN obtain information


  via the optic nerve
• what does the SCN do

  sends signals to the pineal gland directing it to increase production of the hormone melatonin at night
• what hormone is produced by the pineal gland at night

  melatonin
• what does melatonin do

  induces sleep by inhibiting the brain mechanisms that promote wakefulness
• resetting of the biological clock with exogenous zeitgebers is known as:

  entrainment
• when is the biological clock free running 


  when the biological clock operates in the absence of any exogenous cues
• what is the dominant zeitgeber

  light
• another dominant zeitgeber

  social cues like:

  socially determined mealtimes
• AO3 - supporting evidence siffre

  french cave explorer

  seperated himself from the influence of exogenous zeitgebers like natural light for 6 months inside a cave
• AO3 - siffres findings

  at first his sleep pattern was erratic but settled to a regular pattern of 25 to 30 hours

  after resurfacing he felt that he'd lost days and thought he was underground for much less time than he actually was
• who was the french cave explorer

  michel siffre
• what did michel siffres study find out

  found that circadian rhythms persist despite isolation from natural light which demonstrates the existence of an endogenous clock
• AO3 - michel siffre criticism

  methodology - he was restricted from natural light but not artificial light as it was thought that artificial light did not affect circadian rhythms
• AO3 - supporting evidence czeisler

  researched 24 men and women who lived a month in subdued light and tried to place them in an artificial sleep-wake cycle of 28 hours whilst monitoring body temperature and chemistry
• who conducted the living in subdued light study

  czeisler
• AO3 - czeisler findings

  was able to alter circadian rhythms to 22 and 28 hours

  suggested that artificial light as an exogenous zeitgeber can have an impact on circadian rhythms
• AO3 - supporting evidence morgan

  mutant hamster study

  found that if mutant hamsters are bred to have a circadian rhythm of 20 and their SCNs are transplanted into normal hamsters, the normal hamsters display mutant rhythms

  • body temperature rhythm persists without SCNs so there must be another internal clock
• AO3 - morgan hamsters criticism

  generalisability - humans are biologically more complex and would respond differently to manipulations of their circadian rhythms (exogenous zeitgebers like social cues would affect this)
• AO3 - irl application term

  chronotherapeutics
• AO3 - irl application chronotherapeutics

  people know when to take medications to avoid side effects and vulnerability

  affects the effectiveness of the medications

  e.g blood pressure meds work better if taken before bed
• AO3 - shift workers

  shift workers on a rotating schedule need more than a week between each rotation to allow their SCN to adjust which improves productivity and tiredness
• what are the internal factors called that affect the biological clock

  endogenous pacemakers
• what are the external factors called that affect the biological clock

  exogenous zeitgebers