biological rhythms

• biological rhythm

  cyclical variation over some period of time in physiological and psychological processes
• circadian rhythms

  the body's 24 hour clock that keeps our sleep/wake cycle
• endogenous pacemakers in circadian rhythms

  internal biological clock

  suprachiasmatic nucleus (SCN) in the centre of human head

  cluster of neurons in the hypothalamus

  obtains info about light from retina, connects to pineal gland to produce/reduce melatonin

  light directly impacts scn functioning
• exogenous zeitgebers in circadian rhythms

  external time giver

  light is the main EZ for humans

  entrain (reset) free running biologica clock to keep in sync with external world

  SCN receptors are sensitive to changing light levels

  rods and cones in retinas detect light changes
• sleep/wake cycle

  low light levels at night detected by retina causes the suprachiasmatic nucleus to send signal to pineal gland, directing it to increase melatonin

  melatonin induces sleep by inhibiting brain mechanisms

  sleepyy

  high light levels are detected by retina which causes the optic nerve to activate the SCN, signalling pineal gland to reduce melatonin

  woke
• evaluating endogenous pacemakers - morgan 1

  removed SCN in hamsters

  disrupted their sleep wake cycle (slept but with no predictable pattern)

  shows SCN is pivotal in controlling the cycle of sleep, if it wasnt pivotal there'd be no change!
• evaluating endogenous pacemakers - morgan 2

  transplanted SCN of genetically engineered shorter circadian rhythm hamster of 20h into control of 24h

  new hamster adopted shorter circadian rhythm

  shows the influence of the SCN as there'd be no change in the cycle if it wasn't important

  • small????????????
• exogenous zeitgebers evaluation - siffre

  siffre spent six months in a cave in texas yeehaw

  no light or sense of time

  wired to computer, videod

  initially erratic rhythms, soon settled into own periods of activity and inactivity. 25 hour day, lost count of 28 days

  shows how EP's are entrained by EZ's and they're necessary for sleep/wake cycle

  • established caver, used to light and dark
• evaluating exogenous zeitgebers - shift work

  night shifts have practical application

  total darkness during day (sleeptime) means more melatonin so better sleep

  brighter lights to reduce melatonin production at night means better workers and less accidents

  shift change minimum 5-7 days so body can get used to the change

  Yay economy
• ultradian rhythm

  rhythm occurs more than once every 24hrs
• studying ultradian rhythms

  sleep laboratory

  volunteer connected to EEG wire, EOG wire (eye movement) and EMG wire (muscle movement)
• 5 stages - NREM

  1. alpha waves, relaxation, easily woken
  2. alpha and theta waves, K-complexes indivcate brain response to environment without waking
  3. theta and delta waves, deeper sleep, more difficult to wake, reduced muscle movement
  4. delta wave >50%, deepest sleep. temp, hr, respiration at lowest
• 5 stages - REM

  5. EEG reads activity similar to waking, no muscle movement, sleep paralysis, EOG detects rapid eye movements from side to side
• sleep cycle

  happens over 90 minute blocks, 5 stages

  
• ultradian rhythms evaluation - evidence

  dement and kleitman (1957) studied 9 participants for 61 nights in a sleep lab, found the two distinct sleep types

  + controlled, scientific evidence for predictable stages in the sleep cycle

  + reliable, quantitative data

  -sleep lab, but +61 nights
• ultradian rhythms evaluation - d&k ext

  when D&K woke up p's during REM sleep, 79% said they had been dreaming, compared to only 7% woken in NREM

  suggests dreaming is more likely to occur in REM than NREM, potentially due to brains activity
• infradian rhythm

  cycle occuring less than one a day; infrequent
• menstruation

  menstruation is an infradian rhythm governed by monthly changes in hormone levels regulating ovulation

  EP = hormones, EZ = pheromones
• menstruation cycle

  rising oestrogen levels cause ovaries to prepare egg

  high enough oestrogen levels cause surge in lutenising hormones

  egg is released (ovulation)

  progestorone helps womb lining grow thicker to prepare for pregnancy

  no pregnancy means the womb lining must leave the body, causing the bleed
• mcclintock's early observations

  identified synchronisation of female menstruation among own dormitory friends

  concluded 135 women 17-22 became synchronised due to pheromones
• evaluating infradian rhythms - sweaty lip study

  mcclintock and stern conducted 10y longitudinal study on 29 menstruaters

  pheromones collected from 9 with irregular ovulation

  pads containing pheromones wiped under noses of other 20

  found the cycle synchronised, lengthened/shortened

  shows the impact of EZ's on EP
• evaluating infradian rhythms - adaptive

  menstruation together to become pregnant at the same time is adaptive to ensure babies losing their parent after birth would still have milk

  additionally, presence of men shortens period cycle so theres more chances for pregnancy
• evaluating infradian rhythms - methodology

  methodological limitations in researching infradian rhythms due to a myriad of factors that affect the cycle

  confounding variables

  hard to establish c+e