Exogenous zeitgebers and endogenous pacemakers

SCN - endogenous pacemaker

• The SCN receives information about light directly from the optic chiasm, even when our eyes are closed
• Information is passed to the pineal gland, which increases  or inhibits melatonin production depending on light levels
• It is one of the primary endogenous pacemakers in mammals

Melatonin and the pineal gland - endogenous pacemakers

• information is passed from the SCN to the pineal gland
• The pineal gland increases or inhibits production of melatonin (the sleep-inducing chemical) depending on day length and light levels
• Melatonin has also been suggested as a causal factor in seasonal affective disorder

DeCoursey (2000)

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