Biological Functions Related to the Human Sleep-Wake Cycle

During NonREM Sleep:

• heart rate decreases and stabilizes
• breathing pace slows and steadies
• muscles relax
• blood vessels dilate (open wider)
• blood flow to muscles increases
• blood pressure decreases
• metabolic rate decreases about 20% from that during wakefulness

During REM Sleep:

Tonic Functions - occur throughout REM sleep - include:

• sleep paralysis
• increased brain temperature
• swelling of certain organic tissue
• suppressed EMG

Phasic Functions - occur periodically during REM sleep - include:

• rapid eye movements
• tongue movements
• muscle twitches
• variation in heart rate
• variation in blood pressure
• variation of breathing rate

Hormones released by pituitary gland: (1)

• Melatonin - released at night, during deep sleep.
• Growth hormone - secreted at the beginning of deep sleep. (This coincides with the patterns of sleep across the ages.)
• Thyrotrophin - stimulates the thyroid gland during deep sleep. The thyroid gland regulates the body's use of energy.

Temperature: (1)

An average, healthy person's body temperature starts to decrease at about eleven PM. It then reaches its lowest at about 4 AM. It continues to rise during the morning. After a slight mid-afternoon dip, the temperature will rise to it's highest during the early evening. The range in body temperature throughout the day is typically about 1.1 degrees Celsius (2 degrees Fahrenheit).*

Cognitive Function:

During the night, humans have less concentration. Our ability to estimate time becomes worse. Accuracy in simple arithmetic deteriorates. Our arithmetic becomes worse. It even becomes harder for us to do simple, repetitive tasks. The lowest point of these disabilities occurs around 3:00 AM. (2)

All of these functions are synchronized in Circadian Rhythms to our biological clock.

(1) Morin MD, Charles M. Relief from Insomnia: Getting the Sleep of Your Dreams. New York: Doubleday Maintreet Books. 1996.

(2) Coleman, Richard M. Wide awake at 3:00 A.M. By Choice or by Chance? New York: Freeman and Co., 1986. 195 p.

*Original Graphic by Gerry Wyder.