Biological Rhythms

• Biological rhythms have an important influence on the way in which body systems behave.

  They are controlled by endogenous pacemakers and influenced by exogenous zeitgebers.
• Endogenous pacemaker - internal/biological body clock

  Exogenous zeitgeber - external change in the environment
• Biological Rhythms:

  > Infradian

  > Circadian

  > Ultradian
• Infradian rhythms - last longer than 24 hours e.g. female menstrual cycle (28-35 days)
• Circadian rhythms - last for 24 hours e.g. sleep-wake cycle (in any 24 hour period, we are either awake or asleep)
• Ultradian rhythms - last less than 24 hours e.g. sleep stages (5 stages that last 90 minutes each)
• Infradian rhythm - menstrual cycle:

  > an endogenous system that lasts between 28 and 35 days

  > day 1: pituitary gland releases FSH, which activates the release of oestrogen from the ovaries and causes an egg to mature

  > increased oestrogen = increased LH (from pituitary gland) which promotes release of the egg

  > oestrogen develops womb lining and progesterone thickens it, to prepare for pregnancy

  > if pregnancy does not occur, womb lining is shed and cycle begins again

  > can be affected by exogenous factors e.g. stress, pheromones
• Infradian Rhythms AO3:

  :( RTC - Russell - menstrual cycle affected by both exogenous and endogenous

  BUT low control over extraneous variables (field experiment)

  :) Evolutionary psychologists
• Ultradian rhythm - sleep stages:

  > cycle lasts 90 minutes and consists of 5 stages

  > alternates between REM (rapid eye movement) and NREM (non rapid eye movement) sleep

  > a person can experience up to 5 cycles per night that repeat in rhythmic pattern
• Sleep Stages - 1 and 2:

  > NREM - light sleep where a person may be easily woken

  > Stage 1 - alpha waves

  > Stage 2 - alpha waves continue, but occasional sleep spindles (high frequency to stop awakening) or K-complexes (reactions to external noise)
• Sleep Stages - 3 and 4:

  > NREM - deep sleep or slow wave sleep

  > delta waves with lower frequency and higher amplitude

  > difficult to wake someone
• Sleep Stages - 5:

  > body is paralysed

  > brain activity resembles an awake brain

  > theta waves and rapid eye movement (REM)

  > dreams often experienced
• Ultradian rhythms AO3:

  :) Practical applications - sleep deficit in old age (stage 4)

  :) Scientific methods

  :( Low ecological validity - research in artificial settings
• Circadian rhythm - sleep-wake cycle:

  > controlled by suprachiasmatic nucleus (endogenous pacemaker)

  > less light (exogenous zeitgeber) is received by retina as it gets dark - sends information to SCN which stimulates the pineal gland to release melatonin and promote sleep

  > when retina detects light again, the SCN stops stimulating the pineal gland, which inhibits the release of melatonin and promotes wakefulness
• Circadian rhythm AO3:

  :) RTS - DeCoursey (chipmunks)

  BUT animal bias

  :) RTS - Siffre (cave for 6 months)

  BUT lacks ecological validity
• Sleep-wake cycle - application - disruption:

  > Can be disrupted through jet lag and shift work - leads to difficulty sleeping, decreased attention, digestive problems

  > Maintain the cycle by - keeping to local times for eating and sleeping, using black out curtains, avoiding screens at night