circadian rythyms

• What are circadian rhythms?

  • A pattern of behaviour that occurs or reoccurs approximately every 24 hours  and which is set and reset by environmental light levels
• Sleep wake cycle

  • The sleep-wake cycle is an example of a circadian rhythm, which dictates when humans should be asleep and awake. Over a 24 hr cycle 
• What does the scn do?

  1. Light provides primary input to this system, as external cue for sleeping or waking.
  2. Light detected by the eye, -> sends messages concerning the level of brightness to the suprachiasmatic nuclei (SCN).
  3. The SCN then uses this information to coordinate the activity of the entire circadian system.
• • The circadian rhythm dips and rises throughout the day between 2-4am and 1-3pm where sleep drive is strongest
• the role of homeostasis

  • Sleeping and wakefulness are not determined by the circadian rhythm alone;also by homoeostasis.
  • When an individual has been awake for a long time, homeostasis tells the body that there is a need for sleep because of energy consumption.
  • This homeostatic drive for sleep increases throughout the day, reaching its maximum in the late evening, when most people fall asleep.
• Support-counter idigographic 

  One strength of this circadian rhythm is that there has been significant evidence to support it, one key example is Micheal siffre’s cave study in which he spent 2 months in caves of southern alps (no light/sound) and found his circadian rhythm was still between 24-25 hrs , further showe by wever who's studied living in ww11 bunkers for two weeks and found the same-shows body's internal clock is set to 24-25 hrs in the absence of external cues which supports the timings of the sleep wake cycle 
• However there are issues with many of these studies,in many cave studies exposure to dim artificial light such as torches was not controlled and in wever they had meal times where there was light, (confounding variables) it was assumed only natural light affected our biological rhythms however research by czeilser found that dim artificial lighting could adjust rhythms , lacks validity and we can be sure the sleep wake cycle can vary more 
• application, eg. by increasing understanding on the best time to administer drug treatements, eg. risk of a heart attack is greatest in the early morning so drugs are taken at night but not released until dusk, peak times where treatement will be most effective, however research showing things  negatively impacting a person and interfering with circadian ryhyms like shift work, this leads to desynchronization of the rytyms and adverse cognitive and physiological effects - 3 times more likely to suffer from heart disease as a result of stress from adjusting to sleep wake cycles 

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• suggests light is the main influecne in sleeping and waking however psychologists have looked into other factors which have just as much if not more inlfuence.example is buhr who looked into the effect of temperature and found the scn  transforms information about light levels into neural messages that set body's temperature, this fluctuates in 24 hour period and small changes can affect the body clock, he found that changes in temperature set timing of cells in the body, although light may be a trigger temperature is more important than light in setting circadian rythyms 

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