circadian rhythms

• Circadian rhythms - biological rhythms 


  All living organisms subject to biological rhythms which exert important influence on way in which body systems behave

  Governed by two things - body internal biological 'clocks' which are called endogenous pacemakers and external changes in environment known as exogenous zeitgebers

  Circadian rhythms last around 24 hrs - eg sleep wake cycle, core body temperature
• Sleep wake cycle 


  The fact we feel drowsy when it's nighttime and alert during the day demonstrates the effect of daylight an important exogenous zeitgeber on our sleep wake cycle

  Sleep wake cycle also governed by internal (endogenous) pacemaker - biological clock called the superchiasmatic nucleus(SCN) - what if biological clock was left to its own devices without the influence of external stimuli such as light (free-running) if we had no idea whether it was night or day would we still fall asleep and wake up at regular times?
• Other research


  Jurgen Aschoff and Rutger Wever convinced group of pets to spend four weeks in a world war two bunker deprived of natural light , all but one participants (who's sleep/wake cycle extended to 29 hours) displayed a circadian rhythm between 24 and 25 hours.

  Suggests natural sleep wake cycle may be slightly longer than 24 hours but it is entrained by exogenous zeitgebers associated with our 24 hour day.
• Siffre 


  Siffre spent several extended periods underground to study effects on his own biological rhythms - deprived of exposure to natural light (had artificial lamp) and sound, but with access to adequate food and drink - he resurfaced in September thinking it was mid august

  Decade later he performed a similar feat but for six months in a Texan cave

  In each case his free running biological rhythm settled down to one that was just beyond the usual 24 hours (around 25hours) although he did continue to fall asleep and wake up on a regular schedule.
• Shift work


  Research provides an understanding of the adverse consequences that occur when circadian rhythms are disrupted

  reduced concentration at around 6 in the morning - most mistakes made

  shift work and poor health relationship - shift worker three times more likely to develop heart disease

  real world economic implications - how to best manage worker productivity

  However other studies say divorce rates due to missing important events - not entirely biological
• Medical treatment 


  Used to improve medical treatments - circadian rhythms co ordinate number of body basic processes such as heart rate digestion and hormone levels - these rise and fall during day which leads to chronotherapeutics - how medical treatment can be administered in a way that corresponds to a persons biological rhythms

  eg aspirin for heart attacks most effective if taken last thing at night

  --> increases effectiveness of drug treatments
• individual differences 


  Generalisations difficult to make - studies based on very small sample of participants - seems that sleep wake cycle may vary from person to person

  Charles Czeisler found individual difffernces in sleep wake cycle vary from 13 to 65 hours

  --> may be difficult to use research data for anything more than averages