biological rhythms

• circadian rhythms- last about 24 hours eg sleep wake cycle

  ultradian-less than 24 hours eg sleep cycle

  infradian-more than 24 hours eg menstrual cycle
• biological rhythms are processes in body that follow a cycle
• circadian rhythms- about 24 hours


  rhythm is synchronised by master circadian pacemaker, the suprachiasmtic nuclei which is found in hypothalamus

  The SCN must be constantly reset so that our bodies are in synchrony with the outside world. It is regulated by light from our environment in a process called photoentrainment

  eg - sleep wake cycle and body temps
• micheal siffre- lives two months in a cave, no daylight, no clocks, no radio, only thing that infouenced him was his internal body clock, spent 61 days underground and came out on 17th thinking it was 20th

  -mind had lost track of time but hs interna body clock still intact,had not lost track of circadio rhythms , settled into a rythm of just over 2 hours, w know this as he teleephoned his workers whenever he woke.
• silver- removed SCN from hamsters- lost their daily sleep wake pattern-Although this was a well-controlled study, it does not prove on its own that the SCN is the body-clock. By removing the SCN the researchers may have also damaged other areas nearby and it could have been this that damaged the activity cycle.
• infradian- eg is seasonal affectove disorder SAD, may be due to the disruption of the sleep/wake cycle and this is the result of long periods of daily darkness during winter.The hormone melatonin appears to be the cause of SAD. At night the pineal gland secretes melatonin until dawn when there is an increase in light. In winter the lack of light in the morning means the secretion process goes on longer. This has an effect on the production of serotonin -trteatment- phototherapy
• Endogenous pacemakers (body clocks) are centres in the brain that play a main role in controlling biological rhythms. The clock is endogenous which means it is part of the organism, not part of the environment. The clocks help the organism to anticipate what is coming e.g. night. This clock needs to be reset with the changing seasons so that the organism adapts to the changing levels of light. The clock is reset every day by cues in the environment (exogenous zeitgebers).