Our body, as well as bodies of all animals exposed to sun, are ruled by the day and night cycle. Our biological clock is set in this pattern so strongly, that even when we are not exposed to changes in light, we will roughly follow 24h sleep-wake cycle. This cycle guides not only when we feel sleepy, but also our metabolism, hormonal balance (including our hunger/satiety hormones), ….[from book]. Any disruption has a downstream effect to all these processes.
This cycle is now internalized and is guided by
– Sleep pressure mediated by adenosine
– Sleep onset mediated by melatonin based on light exposure
[add explanation of melatonin vs. adenosine vs. cortisol]