Your Inner Clock
A pacemaker region of your brain teams up with light cues from your environment to control your body's sleeping and waking schedule.
The Clock in Your Brain
You have a biological clock, and it has nothing to do with planning your family. The suprachiasmatic nucleus (SCN) is part of the brain’s hypothalamus. The hypothalamus is the center of many homeostatic processes that aim to keep your body's processes in optimal balance. The SCN houses your body's sleepiness and alertness clock. Light cues from the environment trigger the production of adenosine throughout the day. When light becomes scarce, the SCN triggers the production of melatonin, a hormone that induces sleepiness. As melatonin increases, cells in your brain stem begin the work of slowing down some processes for the night's sleep ahead. After you fall asleep, your body breaks down adenosine as melatonin becomes more plentiful.
Your pineal gland is a tiny, pine-cone shaped organ in your brain, secretes melatonin which is the main brain chemical associated with sleep. Adenosine is melatonin's opposite number, the body chemical that builds up during your waking hours. (See The Clock in Your Brain. ) Some chemicals that you ingest have an impact on your alertness cycle as well. Caffeine can keep you alert through periods of initial sleepiness, but it can interfere with your ability to fall asleep. Alcohol may seem to be a good idea at bedtime, as it is a depressant. You may fall asleep on time after having a few drinks, but you are more likely to wake mid-cycle when the alcohol effects wear off.
When the Timing is Off
Any conditions that alter the natural light cues can interrupt the cycle of melatonin production and the sleep/wake cycle. When you travel by jet to another part of the world, you experience a day of either additional hours of natural light, or too few hours of natural light. Your body goes through a sluggish, sleepy phase until it adjusts to the new schedule. Similarly, night workers, who must sleep during the day, are diametrically opposed to their natural sleep wake cycle. They often have to make such adjustments as keeping extra-bright lights on in the workplace all night, and sleeping in a room completely devoid of light during the day. Even the limited light during long winter months, can throw your inner clock out of whack.