endogenous pacemakers and exogenous zeitgebers

• Effect of Endogenous Pacemaker on the Sleep-Wake Cycle

  • Endogenous pacemakers are sometimes referred to as an internal biological clocks. The suprachiasmatic nucleus (SCN) is a collection of nerve cells behind the hypothalamus in each hemisphere
• Effect of Endogenous Pacemaker on the Sleep-Wake Cycle 2

  • The nerve fibres (from the eye) cross the optic chiasm to the visual area of cerebral cortex with the SCN lying just above. It receives information from here about light.
  • It maintains the sleep-wake cycle by passing information to the pineal gland about light levels. When it is dark the pineal gland increases the production of melatonin, which induces sleep
• Endogenous Pacemakers Evaluation 1: Reductionist

  • Peripheral oscillators found in other organs have their own circadian rhythms, suggesting the influence on the sleep-wake cycle is more complex than previously thought
• Endogenous Pacemakers Evaluation 2: Research Support

  • Morgan (1955) bred hamsters with circadian rhythms of 20 hours rathe and then transplanted their SCN neurons into the brains of normal hamsters, which subsequently displayed the same rhythm
• Endogenous Pacemakers Evaluation 3: Chipmunks

  • DeCoursey et al. (2000) destroyed the SCN connections in 30 chipmunks and returned them to the wild
  • Many were killed by predators not long after, as they had left their nests at the wrong time of the day
• Effect of Exogenous Zeitgebers on the Sleep-Wake Cycle

  • There are two external factors, known as exogenous zeitgebers, that help regulate the sleep-wake cycle. These are light and social cues.
  • Light can be detected by the eyes but also by the skin. This influences hormone secretion and blood circulation.
  • Social cues such as mealtimes and bedtimes train babies circadian rhythms to match 24 hours
• Exogenous Zeitgebers Evaluation 1: Real World Application

  • Knowledge of exogenous zeitgebers can help decrease the impact jetlag has on our sleep wake cycles by prodviding light and meals at certain times on a plane to match the destination's time zone
• Exogenous Zeitgebers Evaluation 2: Endogenous Pacemakers

  • People who live in the Arctic circle experience around 6 months of total darkness per year. But yet their sleep patterns do not vary.
  • This suggests endogenous pacemakers may be more important
• Exogenous Zeitgebers Evaluation 3: Siffre

  • Siffre believed the date to be a month earlier than it was when he emerged.
  • This suggests that his cycle was icnreased by the lack of external cues