Normal Sleep
 Sleep is a physical and mental resting state in which a person becomes relatively inactive and unaware of the environment. Sleep is characterized by a decrease in body temperature, blood pressure and breathing rate. The brain is active in sleep. Hormones are secreted, kidney functions change and memory is consolidated during sleep.
Sleep is regulated by two brain processes. One is the restorative process when sleep occurs naturally in response to how long we are awake; the longer we are awake, the stronger is the drive to sleep. The second process controls the timing of sleep and wakefulness during the day-night cycle. Timing is regulated by the circadian biological clock located in our brain. This part of the brain, the SCN or suprachiasmatic nucleus, is influenced by light so that we naturally tend to get sleepy at night when it is dark and are active during the day when it is light. In addition to timing the sleep-wake cycle, the circadian clock regulates day-night cycles of most body functions, ensuring that the appropriate levels occur at night when you are sleeping. We need to have continuous sleep that becomes restorative and results in feeling refreshed and alert for the day ahead.
Good quality sleep means that it is continuous and uninterrupted. As we get older, sleep can be disrupted due to pain or discomfort, the need to go to the bathroom, medical problems, medications, and sleep disorders as well as poor or irregular sleep schedules. Establishing a regular bed and wake schedule and achieving continuous sleep helps you sleep in accordance with your internal biological circadian clock and experience all of the sleep stages necessary to reap the restorative, energizing and revitalizing benefits of sleep.
Sleep has two characteristic states. REM (rapid-eye movement) and NREM (Non-Rapid Eye Movement) sleep. In normal sleep the REM and and NREM states alternate in 90 - 110 minute cycles. A normal sleep night has 4 - 5 cycles. Time spent in these states and stages of sleep varies by age. Both states are important to experiencing quality sleep. Getting the right mix and enough of both REM and NREM sleep will help you maintain your natural sleep architecture and have restful and restorative sleep.
NREM sleep occurs approximately 75 - 85% of the night. It is characterized by four stages from light (Stage 1) to deep (Stage 4). As we begin to doze, we enter .
Transitional stage between wake and sleep, light dozing, slow rolling eye movement, easy awakening, occurs 5 - 10% of night.
Onset of sleep, becoming disengaged with the environment, breathing and heart rate are regular and body temperature goes down, muscles relax, larger brain waves, 45 - 50% of total sleep time.
Deepest and most restorative sleep, difficult to arouse, no eye movement, blood pressure drops; breathing and heart rate slower; energy regained; and hormones are released for growth and development, 10 - 20% of total sleep time.
20 - 25% of night
Rapid eye movement, a darting back and forth, first occurs about 90 minutes after falling asleep and increases over later parts of the night. REM sleep is necessary for providing energy to the brain and body. The brain is active and dreams occur. The body become immobile and relaxed, muscles shut down; breathing and heart rate may become irregular; important to daytime performance and contributes to memory consolidation.
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