What is Sleep?

 

Sleep is a state of natural rest in which we spend approximately one third of our lives. The physiology of sleep is able to be studied by means of a technique called polysomnography, which records measurements of activity of the brain and muscles (including the heart), eye movements and breathing efficiency.

Why Do We Need Sleep?

Most people need about eight hours of quality sleep every night, and just about anyone who has missed a night of sleep can tell you how miserable sleep deprivation can feel. Yet, despite decades of research, the exact function of sleep remains somewhat mysterious. While we know quite a bit about different types of brain activity and hormonal changes that occur during sleep, we don't truly understand exactly what function sleep performs. In fact, we have learned the most by discovering what happens to people when they don't get enough sleep.

What Exactly Happens to Our Bodies and Minds While We Are Sleeping?

 

Healthy, restorative sleep consists of five separate stages that occur during 90 to 110-minute cycles throughout the night. Each of these stages is marked by differences in the quality of brainwaves generated. Stage 1 consists of light sleep; stages 2-4 involve successively deeper sleep, and brainwaves slow down. The final stage in the cycle is known as REM sleep. REM refers to the "rapid eye movement" that occurs during this portion of the sleep cycle, and this is when most dreaming is thought to occur. In fact, REM sleep is as different from non-REM sleep as sleep is from being awake. While the brain is very active during this cycle, most muscles are paralyzed.

 

As the night progresses, the amount of time spent in any one stage varies, thus underscoring the need for a full night of uninterrupted sleep. Hormonal levels change with sleep, too. Cortisol, a stress hormone, decreases, while levels of melatonin and growth hormone increase. These hormones appear to play a role in regulating fundamental bodily processes, including childhood growth and adult muscle maintenance and repair.

 

 

What Happens When We Don't Get Good Sleep?

 

Insufficient sleep appears to play a role in a variety of health issues, including weight control, muscle regeneration and maintenance, and childhood growth. Because hormone levels change during sleep, interfering with sleep throws off basic body chemistry, which can lead to long-term health problems.

 

Psychological health clearly suffers from either insufficient amounts of sleep or poor quality sleep. As reflected in the 2002 Sleep in America poll, daytime sleepiness correlates with increased feelings of anger and dissatisfaction with life [1]. Other studies have shown that sleep deprivation impairs judgment, reaction time, daytime alertness and certain types of memory [2].

 

Inadequate sleep has been linked to serious social costs as well. The National Highway Traffic Safety Administration reports that insufficient sleep contributes to 100,000 car accidents per year. One study estimates that sleep deprivation costs Americans at least $92 billion dollars per year [3].

 

References

[1]   http://www.sleepfoundation.org/2002poll.cfm

[2]   http://www.sleepfoundation.org

[3]   Stoller MK. Economic effects of insomnia. Clinincal Therapy (1994) 16:873-897, discussion 854