biological rhythms

biological rhythms

  • governed by endogenous pacemakers and exogenous zeitgebers

  • endogenous pacemakers: internal biological clocks

  • exogenous zeitgebers: changes in the environment

  • types of rhythms : ultradian, infradian, circadian

  • ultradian: multiple times during the day

  • infradian: longer than a day

  • circadian: 24 hours

circadian rhythms

  • 24 hours

  • examples: sleep/wake cycle and core body temp cycle

  • sleep/wake: controlled by daylight (EZ) and and SCN (EP) - lies just above the optic chiasm and provides eye with info about daylight

  • Siffre’s cave study: spent 2 months in a cave deprived of light and found that his ‘free-running’ circadian rhythm eventually settled to one around 25 hours

  • Aschoff and Wever: group of participants spent 4 weeks in a WW2 bunker deprived of light and all but one participant displayed a circadian rhythm of 24-5 hours (suggested that EZ associated with 24 hour times train sleep/waking cycles)

  • Folkard: group of 12 people who lived in a dark cave for 3 weeks with a clock that they would use to know when to fall asleep (sped up clock and found that rhythm became 22 hours - affect of EZ)

infradian rhythm

  • longer than 24 hours

  • examples: menstrual cycle, seasonal affective disorder

  • endogenous pacemaker: menstrual cycle is governed by changes in hormone level to regulate ovulation (takes 28 days to complete) - rise in oestrogen and progesterone

  • exogenous zeitgeber: Stern and McClintock suggested that menstrual cycles can synchronise from pheromones →29 women with irregular periods, pheromones gathered from 9 at diff stages of cycle, pads rubbed on upper lips of other participants and found that 68% changed cycle closer to the pheromone cycle they were given (‘odour donor’)

  • SAD: depressive disorder triggered by winter months and lack of daylight, psychologists suggest this is because melatonin is produced until increased daylight which has a knock-on effect in production of serotonin in the brain

  • SAD can also be classed as a circadian rhythm as it may be due to disruption of sleep/waking cycle from prolonged darkness

ultradian rhythms

  • multiple times within 24 hours

  • example: stages of sleep (5 stages that span 90 mins - characterised by brainwave activity)

  • stage 1/2: most easily woken →in stage 1 brain waves are high frequency and have short amplitude (alpha waves) and in stage 2 this continues with occasional changes in pattern (‘sleep spindles’)

  • stages 3/4: deep sleep/slow wave sleep → delta waves with lower frequency and higher amplitude

  • stage 5: (REM sleep) body is paralysed but brain activity resembles awake → theta waves and rapid eye movement (REM)