Biological Rhythms 

Circadian, Ultradian and Infradian Rhythms.

Jet lag and Shiftwork 

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  • Biological Rhythms
    • Circadian
      • 24 hour period
      • Sleep-wake cycle regulated by melotonin released by pineal gland when dark
      • Rats - SCN removed, abolishing SW cyle
      • Genetically bred hamsters - 20hr circadian rhythms, SCN transplanted into 'normal' rats, who then developed 20hr rhythm
      • Siffre - 6 months in cave, scientists called to turn lights on and off. He recorded BP, and a series of mental, memory, and physical tests.
        • 1st month - 26hr cycle, suffering from loneliness and depression. 6th month - eye sight worsened, had physical and mental troubles.
        • ? Useful - blind people and astronauts.
        • Support: WW2 bunker - no enviromental cues, most had cycle of 24-25hrs (some had 29hrs)
        • X Not representative - people have different biological rhythms
        • Support: 12 ppts, 3 weeks, slept 11:45pm to 7:45am. Clock changed from 24 to 22hrs. Ppts stayed at 24 hours
      • Deterministic
      • Supports the biological approach
      • Support: Blind man - extraneous factors such as clocks, but still had little effect on making it difficult for him to function
    • Ultradian
      • Stage 1: Light sleep, muscle activity slows down
        • Stage 2: Breathing and heart rate decreases
          • Stage 3: Deep sleep, braid generates slow delta waves
            • Stage 4: Very deep sleep, little muscle activity, lots of brain delta waves
              • Stage 5: REM, dreaming, very active brain
      • 9 ppts wired to EEG (measures brain activities). Ppts woken when patterns changed and reported what they were experiencing.
        • 80% during REM reported dreaming
        • 20% during NREM reported dreaming
        • REM dreams were more intense
      • Deterministic - no control over sleeping patterns
      • Less than a day
    • Infradian
      • Longer than 1 day
      • Controlled mainly by hormones - endogenous, secreted by the pineal gland so is influenced by day light
      • 10yr long stud, 29 women (20-35yrs) with history of irregular periods.
        • Samples of pheromones from 9 of these at certain points of menstruation (cotton pads), pads then wiped under noses of 20 others daily. 68% women's periods change in response.
      • Many exogenous factors such as stress, diet and other women who are living with them
      • SAD - has seasonal pattern. Suspected link to reduced sunlight.
        • Light stimulates the hypothalamus which controls mood sleep and appetite. Lack of sunlight prevents it from working properly.
      • Deterministic- Severe PMS - mental disorder - effects law
      • Light therapy - sufferes report that daily use of light box reduces symptoms
    • Jet Lag
      • Body's effected by sudden time changes - takes the SCN several cycles to sinc.
      • Winter et al calculated that for every hour time difference it takes 1 day to recover.
      • Symptoms: Insomnia, mild depression, fatigue, and performance effects
      • East to West = phase delay (causes less jet lag)
      • West to East = phase advance (causes more jet lag)
        • Going to bed earlier is easier than staying up later
          • East to West = phase delay (causes less jet lag)
      • Baseball players. 3hr time difference. When west went to east won 44% of the time. When East went to West they won 37% of the time.
        • Awake during circadian trough - disrupts rhythm
    • Shift Lag
      • Causes de-synchronisation of the body clock
      • Midnight = lowest cortisol levels.
      • 4am = lowest core body temperatue
      • Causes sleep deprivation - 1-2hrs less sleep in the day. Particularly effects REM
      • 3 Times increased risk of heart disease when working more than 15yrs on night shifts.
      • Social disruption leads to higher divorce rates
      • Rotating shifts (alternating daily) are more harmful than non-fluctuating shifts (which disturbs the biological rhythm less)
      • Forward roatating shifts change every 3-4 days (6am-2pm, 2pm-10pm, 10pm-6am). Easier to adjust- better work/social life.
      • 10 studies reviewed. Melatonin successful in helping ppts sleep when taken daily.
      • 31 males exposed to very bright, bright, normal and dim light. Circadian rhythm adjusted by +5hrs, +3hrs, +1hr, and -1hr.
        • Decreased disasters


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