Biological Rhythms

• Biological rhythm - a bodily function regulated by your internal clock
• 3 types of biological rhythms:

  • infradian
  • ultradian
  • circadian
• Infradian rhythm - occurs less than once a day (lasts more than 24 hours); examples: menstruation, hibernation, seasonal affective disorder (SAD)
• Ultradian rhythm - recurring frequently throughout a 24 hour period; examples: feeding, sleep cycle (stage 1- not quite asleep/ REM, stage 4- almost unwakeable
• Circadian rhythm - recurring naturally on a 24 hour cycle; examples: sleep/waking, body temperature, metabolic activity; changes influenced by internal and external environments through endogenous pacemakers and exogenous zeitgebers
• Endogenous pacemakers - internal bodily systems that control biological rhythms
• Endogenous pacemaker in the sleep/ wake cycle - the suprachiasmatic nucleus (SCN) found in the hypothalamus receives light through the eyes; when light levels drop, impulses are sent to the pineal gland which secretes melatonin causing sleepiness; when light levels increase, melatonin decreases making us more alert
• The suprachiasmatic nucleus is known as the body clock
• Exogenous zeitgebers - external influences that help us regulate our timings, such as, light and noise
• Guo et al (2020) - found that submariners (who don't have exposure to normal zeitgebers and work on a 6 hour on/ 12 hour off schedule) suffer from severe circadian misalignment, leading to decreased cognitive performance
• Siffre (1975) - 179 days underground without natural exogenous zeitgebers; 151 "days" had passed on his schedule; days lengthened to 25-30 hours; body clock had desynchronised
• Disrupting biological rhythms leads to jet lag and shift lag
• Jet lag - the effects we experience after crossing into a different time zone; takes several cycles to re-synchronise to a new environment; experience symptoms such as, disturbed sleep, fatigue, stomach problems, mood changes
• 2 types of adjustment for jet lag:

  • Phase delay - travelling east to west extends your day
  • Phase advance - travelling west to east shortens your day
• Shift lag - the effects of working rotating shifts or night shifts; effects including higher stress levels, more at risk of addiction, insomnia, excessive sleeping, unhealthy eating habits
• Knutsson et al (1986) - found that individuals who worked night shift for more than 15 years were 3X more likely to develop heart disease than non-shift workers