Two body processes control sleeping and waking periods. These are called sleep/wake
homeostasis and the circadian biological clock.
With sleep/wake homeostasis, the longer you are awake, the greater your body senses
the need to sleep. If this process alone was in control of your sleep/wake cycles,
in theory you would have the most energy when you woke up in the morning. And you
would be tired and ready for sleep at the end of the day.
But your circadian biological clock causes highs and lows of sleepiness and wakefulness
throughout the day. Typically, most adults feel the sleepiest between 2 a.m. and 4
a.m., and also between 1 p.m. and 3 p.m. Getting plenty of regular sleep each night
can help to balance out these sleepy lows.
Your body’s internal clock is controlled by an area of the brain called the SCN (suprachiasmatic
nucleus). The SCN is located in the hypothalamus. The SCN is sensitive to signals
of dark and light. The optic nerve in your eyes senses the morning light. Then the
SCN triggers the release of cortisol and other hormones to help you wake up. But when
darkness comes at night, the SCN sends messages to the pineal gland. This gland triggers
the release of the chemical melatonin. Melatonin makes you feel sleepy and ready for