Sleep/Wake Cycles

Sometimes you drift off to dreamland before you count your third sheep. Other times you toss and turn half the night before you slip into a fitful sleep. After lunch you may be dragging, yet later, your energy levels soar, just in time for bed. How and when you feel sleepy has to do with your sleep/wake cycles, which are triggered by chemicals in the brain.

Brain chemicals and sleep: 

  • Chemicals called neurotransmitters send messages to different nerve cells within the brain. Nerve cells in the brainstem release neurotransmitters, including norepinephrine, histamine, and serotonin. These neurotransmitters act on parts of the brain to keep it alert and functioning while you are awake.
  • Other nerve cells stop the messages that tell you to stay awake, causing you to feel sleepy. One chemical involved in that process is called adenosine. Caffeine promotes wakefulness by blocking the receptors to adenosine. Adenosine seems to work by gradually building up in your blood when you are awake, leading you into drowsiness. While you sleep, the chemical slowly dissipates.

Sleep processes

  • Two body processes regulate 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 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 and 4 a.m. and between 1 and 3 p.m., which explains those after-lunch yawns. Getting plenty of regular sleep each night can help to offset these sleepy lows.
  • Your internal clock is regulated by an area of the brain called the suprachiasmatic nucleus (SCN). The SCN is located in the hypothalamus. The SCN is sensitive to signals of dark and light. When the optic nerve in your eyes senses the morning light, the SCN triggers the release of cortisol and other hormones to help you wake up. But as night falls and darkness settles, the SCN sends messages to the pineal gland. This gland triggers the release of the chemical melatonin to make you feel sleepy and ready for bed.

Neurotransmitters and your sleep

  • Some neurotransmitters help your body to recharge while you sleep and even help you to remember things that you learned, heard, or saw while you were awake. It seems that the neurotransmitter acetylcholine, which peaks both during REM (rapid eye movement) sleep and while you are awake, helps your brain retain information gathered while you are awake and then “sets” that information as you sleep. So if you study or learn new information in the hours before bed, “sleeping on it” can help you remember it.
  • Other neurotransmitters may work against you as you sleep. Abnormalities with the neurotransmitter dopamine may trigger sleep disorders such as restless legs syndrome.
  • Getting consistent, sufficient levels of sleep can help you feel awake and refreshed during the day, and relaxed and sleepy at night so you’re ready for a long, restful night of slumber.

My Take: Because melatonin levels are regulated, at least in part, by exposure to light, try to sleep in a very dark room. For women, estrogen levels can rise with light exposure, as melatonin and estrogen are linked.  I would also suggest no blue light exposure within an hour of sleeping: That means you, that individual with the cell phone, television, or e-reader. The bedroom is for two things… I’m Dr. Michael Hunter.

The small print: The material presented herein is informational only, and is not designed to provide specific guidance for an individual. Please check with a valued health care provider with any questions or concerns. As for me, I am a Harvard- , Yale- and UPenn-educated radiation oncologist, and I practice in the Seattle, WA (USA) area. I feel genuinely privileged to be able to share with you. If you enjoyed today’s offering, please consider clicking the follow button at the bottom of this page.

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Reference:; Medical Reviewers: Amy Finke, RN, BSN ; MMI board-certified, academically affiliated clinician
Last Review Date: Jan 5, 2014
© 2000-2014 Krames StayWell, 780 Township Line Road, Yardley, PA 19067. All rights reserved. This information is not intended as a substitute for professional medical care. Always follow your healthcare professional’s instructions.

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Harvard AB Yale MD UPenn Radiation Oncology Radiation Oncologist, Seattle area

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