Endogenous pacemakers and exogenous zeitgebers


Endogenous pacemakers and exogenous zeitgebers

Endogenous pacemakers and the sleep/wake cycle

  • The superchiasmatic nucleus (SCN)
    • The SCN is a tiny bundle of nerve cells located in the hypothalamus in each hemisphere of the brain
    • It is one of the primary endogenous pacemakers and is influential in maintaining circadian rhythms
    • Nerve fibres connected to the ye cross in an area called the optic chiasm on their way to the visual area. The SCN lies just above this 
    • It recieves info about light directly from the OC, even when our eyes are closed, enabling the body clock to adjust to changing patterns of daylight whilst we are asleep
  • Animal studies and the SCN
    • DeCoursey destroyed the SCN connections in the brains of 30 chipmunks who were then returned to their natural habitat and observed for 80 days
    • The sleep/wake cycle of the chipmunks disappeared and by the end of the study a significant proportion of them had been killed by predators
    • Emphasises the role of the SCN in establishing and maintaining the sleep/wake cycle
  • The pineal gland and melatonin
    • The SCN passes the info on day length and light that  it receives to the pineal gland
    • During the night, the pineal gland increases production of melatonin- a chemical that induces sleep and is inhibited during periods of wakefulness

Exogenous zeitgebers

  • Exogenous zeitgebers are external factors in the environment that reset our biological clocks through 'entertainment' 
  • In the absence of external cues, the…


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