Biological rhythms

Biological rhythms

Circadian rhythms
1. ~ 24 hours
2. Sleep-wake cycle
  1. External cues i.e darkness, time
    1. Folkard et al - 'day' shortened to 22 hours, endogenous factors took over showing control
  2. endogenous factors control cycle in absence of cues
    1. Suprachiasmatic nucleus - main bodily clock
      1. Pineal gland responsive to light cues. Serotonin -> melatonin
        Melatonin controls sleep wake cycle
      2. Stephan & Zucker - rat SCN distruction disrupted circadian rhythms inc SWC
        Rosenwasser et al - animals fed regularly became active before eating, continued after SCN destruction
  3. Fulton & Bailey - tumours affecting the SCN caused disrupted SWC
  4. Siffre - spent long periods of time in caves. Found SWC stayed around 24 hours
  5. Czeisler et al - individual differences 13-65 hours
3. Cortisol - high levels provide alertness - lowest at 12am, highest at 6am. Explains difficulty in waking up early
4. Biologically determinist
  1. Some flexibility, go to bed early and wake up at normal time
  2. Folkard et al - individual able to maintain 22 hour cycle. Overriding internal clock
Infradian & ultradian rhythms
1. Ultradian rhythms < 24 hours
  1. Sleep stages
    1. Stages 1&2 - relaxed, alpha & theta waves, decreased heart rate & temperature
    2. Stages 3&4 - SWS delta waves, decreased metabolism, growth hormone secreted
    3. REM - dream time, brain activity similar to consciousness, but body paralysed. Paradoxical state
    4. ~ 90 minutes. More REM later in night
    5. Dement & Kleitman - woken in REM normally dreaming, however not exclusive
  2. Rest-activity cycle - 90 minute cycle
    1. Freidman & Fisher - 90 minute pattern between eating & drinking in psychiatric patients
    2. Maintains metabolic processes
2. Infradian rhythms > 24 hours
  1. The menstrual cycle is an example
    1. Russell et al - pheromones can sync menstrual cycles, collecting sweat from one woman and rubbing on the upper lips of other women
      1. Can be controlled by exogenous factors
    2. PMS can be an effect
      1. Dalton - PMS lead to decreased academic achievement, suicide & crime
      2. Schonberg et al - women administered higher shocks to a learner a week before menstruation
      3. Nicholson - only 5% women suffer PMS
      4. Janiger - PMS found in all cultures
  2. Seasonal affective disorder (SAD)
    1. Melatonin & Serotonin levels possible cause. More darkness - more melatonin, causing less serotonin. Low serotonin associated with depression
      1. SAD & PMS inevitable behaviours.
        Johnson - Woman acquitted of murder due to severe PMS
        Born et al - Able to will your body into change. People told to wake up earlier had higher ACTH (stress hormone) levels
    2. Not an infradian rhythm, just disrupted circadian rhythm from sleeping earlier
    3. Phototherapy - treatment using very strong light
      1. Eastman et al - 32% increased from placebo effect
Endogenous pacemakers & exogenous zeitgebers
1. Endogenous pacemakers
  1. SCN nerve cells in hypothalamus
    1. Gets light information as it is just above the optic chiasma. Info still received when eyes shut
  2. Morgan - hamsters bred with 20 hour circadian rhythm. SCN removed and transplanted. 20 hour cycle again shown
    1. Animal research like this causes permanent damage. Ethical issues & cost benefit. Also how generalisable is it to humans?
  3. SCN split in each hemisphere
    1. Ventral SCN - easily reset by external cues
      1. Desynchronisation caused when ventral and dorsal parts are out of phase
    2. Dorsal SCN - less affected by light
  4. Pineal gland produces melatonin which inhibits brain mechanisms for wakefulness
  5. DeCoursey et al - provided evolutionary advantage, Chipmunks without functioning SCN more likely to die. - Awake & night, making noise attracting predators
2. Exogenous zeitgebers
  1. Light
    1. Affects SCN and peripheral oscillators
      1. Contain cryptochrome (CRY) - sensitive to light
    2. Campbell & Murphy - reset circadian rhythms shining light on the back of participants knees
      1. Challenged idea of SIffre cave study that light had no effect
      2. Not replicated
    3. Stevens - artificial light world affects hormone levels, increased cases of cancer
      1. Blue light (in electronics & energy saving bulbs) perfect for resetting circadian rhythm. Can set it an hour back
  2. Social cues
    1. Davidson - mealtimes reset heart & liver cells
  3. Biological system control adaptive advantage - difficult to override when faulty
  4. Temperature
    1. Cold - signal for reduced activity
    2. Warm - time for activity (sleep-wake)
    3. Buhr et al - temperature changes from circadian clock. In turn this regulates other circadian rhythms
      1. Endogenous & Exogenous factors work together to regulate rhythms.
        Total isolation studies are artificial

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	Criado por Brendan Williams mais de 10 anos atrás

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