Internal body clocks that control biological rhythms, circadian rhythms in particular
Suprachaismatic nuclei (SCN)
The most important endogenous pacemaker as it maintains the sleep-wake cycle
Receives information about brightness levels from the eye
Stimulates the pineal gland to release melatonin
Melatonin production increases at night making us fall asleep, and stops during the day causing us to wake up
Exogenous zeitgebers
External factors that control biological rhythms
Light
A key zeitgeber in humans that maintains the sleep-wake cycle
Social cues
Such as meal times, are also zeitgebers that make up for the lack of natural light
Removal of SCN in chipmunks
Their sleep-wake cycles disappeared
The research lacks generalisability as humans respond differently to the removal of their SCN because we are biologically different
People who live in the arctic experience 6 months of darkness all year round, yet their sleeping patterns are still the same, suggesting the sleep-wake cycle is mainly controlled by endogenous pacemakers
