Biological rhythms

• Circadian rhythm

  > 24 hour cycle

  > sleep wake cycle is controlled by the master endogenous pacemaker (suprachiasmatic nucleus) found in hypothalamus

  > eyes notice a change in light as it gets dark and less light is received by the retina

  > sends information to the SCN which stimulates the pineal gland to release melatonin and promote sleep

  > when eyes detect light (exogenous zeitgeber) the SCN is reset which maintains the sleep wake cycle
• Circadian rhythm AO3

  :) RTS Siffre

  DISSCUSSION low population validity

  :) practical applications
• Infradian rhythms

  > longer then 24 hours - menstrual cycle

  > menstrual cycle 28-35 days

  > begins on the first day of period, womb lining is shed

  > pituitary gland releases FSH which activates the release of oestrogen causing egg to mature

  > increase of oestrogen, increases levels of LH

  > oestrogen develops womb lining and progesterone helps it grow thicker, readying for pregnancy

  > if pregnancy does not occur the egg is absorbed into the body and cycle begins again
• Infradian rhythm AO3

  :) RTS Russel - synchronised cycles

  DISSCUSSION low control over extraneous variables

  :) methodological flaws
• Ultradian rhythms

  > less then 24 hours

  > stages of sleep

  > Stage 1 and 2 - NREM - person may easily be woken

  > Stage 3 and 4 - deep sleep NREM - lower frequency and higher amplitude, difficult to wake someone

  > Stage 5 - REM - paralysis, brain activity resembles an awake brain, dreams experienced
• Ultradian rhythms AO3

  :) practical applications

  :) scientific methods

  DISSCUSSION low ecological validity
• Sleep wake cycle AO3

  :) RTS DeCoursey

  DISSCUSSION animal bias

  :) RTS Siffre

  DISSCUSSION lack ecological validity