BIOLOGICAL RHYTHMS

• • Circadian-24hrs. ​
  • An example of a circadian rhythm is the sleep wake cycle. Our body clocks naturally have a cycle of approx 25hrs but we have adapted to a 24hr cycle. Evidence suggests they can range from 13 to 60 hours depending on the individual.
• • Infradian= more than 24hrs. ​
  • An example of an infradian rhythm is the menstrual cycle. This lasts 28 days on average but can range from 23 to 35 days. Ovulation occurs approximately halfway through. Another example is seasonal affective disorder (SAD). This is where someone is affected by clinical depression only duriong winter. Hibernation is another infradian rhythm
• • Ultradian= less then 24hrs​
  • An example of this is the basal rest activity cycle (BRAC) where after 90mins we are fatigued mentally and no longer able to concentrate.
• •  Another ultradian example is the 5 sleep stages:​

  1.Light sleep 2. HR body temp and breathing slow  3.Deep sleep. 4. Very deep sleep. 5) REM sleep​

  This lasts 90 mins then repeates through the night
• • Endo=inside, exo=inside. Essentially internal and external cues/stimuli​
  • ENDOGENOUS PACEMAKERS are internal cues that affect our rhythms. The SCN or superchiasmatic nuclei located in the hypothalamus is the master clock which controls and resets all the rhythm. The SCN is photosensitive and can adapt to meet environmental demands. Other (peripheral) body clocks are controlled by the SCN.
• • EXOGENOUS ZEITGEBERS are external cues such as light and social cues (like meal times) that affect our biological rhythm.​
  • Light is a good example. SCN cells are very photosensitive. When it is dark they tell the pineal gland to release melatonin which makes you sleepy . This is why blue light can contribute to insomnia as it mimicks sunlight and stops melatonin production.
• superchiasmatic nucleus = SCN
• the SCN contains cells that are sensitive to light (photoreceptors).
• when photoreceptor cells detect light they send signals along nerve fibres to the pineal gland.
• the SCN is located within the hypothalamus, which controls many bodily functions.