What is sleep?

What is sleep?

Sleep Centre

What is sleep?

Everybody appreciates a good night’s sleep, but everybody probably also knows what it feels like not to have had quite enough. What is sleep, and why do we sleep?

Sleep is a natural unconscious state where the body becomes inactive, senses become less responsive and the mind becomes unconscious. Sleep revitalises various systems of the body, for example the immune, skeletal and muscular systems. It is also needed for normal cognitive brain function, such as speech, memory and thinking.

However, exactly how sleep works and its full function is not clearly known. It is difficult to determine what sleep is, as you don’t know much about what happens when you are in dreamland and very rarely would someone be aware of the fact that he or she is sleeping at the time.

What happens when we sleep?

A way to define sleep and its stages is to look at brain wave patterns and physiological changes that take place when we sleep.

We sleep in a cycle of between 90 and 110 minutes. The sleep cycle can be divided into non-REM (rapid eye movement) and REM sleep. Non-REM sleep consists of three stages that include light, true and deep sleep. This last about 70 to 90 minutes, followed by REM sleep. We experience between three and five REM stages a night.

Physiological changes that occur during sleep include a slight decrease in temperature, blood pressure and heart rate. This fall in temperature means we use less energy to keep the body warm. Breathing also slows down and becomes more regular. The brain stays active during sleep, and can be even more active than when awake during REM sleep!

During REM sleep more changes in the heart rate and blood pressure take place. This is also the stage when most dreaming occurs.

Another major change that happens during sleep is an increasing in the amount of growth hormone in the body. Physiological activities related to digestion, cell repair and growth are often at its peak during sleep.

Effects of sleepless nights

After only a short amount of lack of sleep, the brain function is already affected and can cause irritability, forgetfulness, lack of concentration, shorter attention span and, of course, tiredness. After ongoing lack of sleep, more parts of the brain are significantly affected, such as language, memory, planning and sense of time. In fact, 17 hours without sleep has the same effect on your brain function and motor skills as a blood alcohol level of two glasses of wine. It can also be bad for emotional and physical health, and rational judgement.

It is believed that lack of sleep has contributed to some international catastrophes, for example the Exxon Valdez oil spill, Chernobyl and Three Mile Island nuclear disasters, and the Challenger shuttle explosion.

Lack of regular sleep may lead to sleep disorders such as insomnia, hypersomnia, sleep apnea, sleepwalking and circadian rhythm sleep disorders. The longest record for going without sleep is 11 days, set by Randy Gardner in 1965.

Bingham, Roger; Terrence Sejnowski, Jerry Siegel, Mark Eric Dyken, Charles Czeisler, Paul Shaw, Ralph Greenspan, Satchin Panda, Philip Low, Robert Stickgold, Sara Mednick, Allan Pack, Luis de Lecea, David Dinges, Dan Kripke, GiulioTononi (February 2007). “Waking Up To Sleep”.The Science Network.Retrieved 25 January 2008.