Why We Sleep - and Why We Don't

Allen Blaivas, M.D. Health Pro
  • Question:  I get tons of sleep a night - at least 8 hours - but I still feel like I need a nap around 1 or each day.  Is this normal?  Is there something I could be doing to avoid this early-afternoon energy crash?

    Dr. Blaivas:

    Thanks for your interesting question.  I covered many pertinent issues in regard to possible sleep disorders in the December blog entitled, “How Do You Know If You Have A Sleep Disorder?”  There is one issue raised in your question that may awaken (pun intended) us to how the body works.

    Sleep and wake in the body is basically determined by two different factors: 1) sleep/wake homeostasis and 2) the circadian rhythm.  Sometimes these drives can work together in enabling us to sleep soundly, whereas other times they compete.

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    First let me define them.  Homeostasis is essentially when a body process works to maintain its status quo.  For example, when we don’t eat for a few hours our body “reminds us” that we should eat by causing our stomachs to growl, making our thought processes a little slower, and giving us hunger pangs, all in order to make us grab a bite of food to eat to have continued energy to function at peak level.  In a similar fashion we have a sleep drive, that reminds us that after a bad night of sleep, we should consider getting to bed a little earlier by making us tired and less alert, with decreased energy the following day.  In addition, the sleep on the night following sleep deprivation is usually deeper.  The converse is also true.  After a good night of sleep or if we wake later than usual, we have a lower tendency to doze and the sleep on the night following may not be as efficient.

    Then there is the concept of circadian rhythm, which is an approximately 24-hour cycle that our body runs on (circa=about, dia=day).  These rhythms are basically regulated by a part of the brain in the hypothalamus called the suprachiasmatic nucleus (SCN), which receives a signal from the retina of the eye in response to light.  The SCN takes the information from the retina on day/night cycles and then signals the body to begin producing hormones.  After exposure to light the SCN causes hormones that stimulate increase activity to be released (i.e., cortisol).  In response to dark, the SCN relays a gland in the brain, called the pineal gland to release melatonin, which is released mostly at night, and lets the body know that sleep should soon be on hand.  Incidentally, it is believed the caffeine keeps us awake by blocking the production of melatonin.  Many essential body functions such as the control of temperature and cardiovascular function, the release of hormones, and the metabolism are under the control of the circadian rhythm or internal body clock.  (Also, see my previous blog on jet lag.)

    Now that I have you thoroughly confused, I will ask you to stay tuned and continue this train of thought in my next blog.  (And hopefully actually answer your question!)

Published On: March 12, 2007