Sleep is an essential part of normal body function. It is cued by the release of a neurotransmitter chemical called adenosine. Other neurotransmitters, serotonine and norepinephrine, keep parts of the brain active while we are awake.
Although scientists have not found brain cells that get tired and ‘need’ to sleep, there appears to be some brain cells that work harder while we are awake while others work harder when we are asleep.
Unlike a baby who will sleep for up to 17 hours a day, an adult generally requires about 8 hours of sleep.
During sleep, you go through 5 or 6 sleep cycles. There are five stages to a sleep cycle:
- Light sleep
- Slower brain function with bursts of brain activity- adults spend 50% sleep time in this stage
- Extremely slow brain waves
- More extremely slow brainwaves
- Rapid Eye Movement (REM)- adults spend about 20% of sleep time in REM sleep.
Stages 3 and 4 combined make up ‘deep sleep’. It is hard to wake someone up from deep sleep and they will feel groggy and disoriented for several minutes after waking. Sound like anyone’s Monday morning?
We all know what happens when we spend too long without sleep. Lack of concentration, impaired memory and irritability are just some of the signs of fatigue.
Drowsiness, the last stage before sleep, is caused by the build up of adenosine in the brain. When a person has been awake for a long time, their cells release adenosine to signal a need for sleep.
Caffeine and other stimulants were shown in a 2005 study to interfere with adrenosine reaching the brain. This results in the brain being unaware that cells have been working for a prolonged time, delaying sleep.
There is a good summary video explaining this 2005 study, courtesy of ScienCentral, available on youtube at http://www.youtube.com/watch?v=l6PxfVQFsiU
Lack of sleep
Did you know that you develop a ‘sleep debt’ when going without sleep for prolonged periods of time? Although people may get used to a sleep-deprived schedule, their judgement, reaction time and other brain functions remain impaired. Eventually the body demands repayment of the sleep-debt.
Sleep deprived people who are tested with a driving simulator or a hand-eye coordination test often perform as badly as people who are drunk.
In the years between 2006 and 2010 in New Zealand, there were 937 vehicle crashes involving 1244 serious injuries and deaths. Although not as large as the number of crashes alcohol was involved in, any number of crashes attributable to sleep is too large. It is so simple to pull the vehicle over and take a 20 minute power nap. Arriving safely at a destination is preferable to not arriving at all.
Health benefits of sleep
Experiments have shown that sleep is linked with both a healthy nervous system and immune system.
In the nervous system, sleep is thought to give brain cells the chance to exercise brain connections that might otherwise deteriorate due to lack of activity.
In the immune system, deep sleep has been linked to the release of growth hormones in children and young adults. Proteins crucial for cell repair are produced in greater quantities during sleep.
The sleep-wake body clock
Our bodies are programmed to sleep at a certain time. Have you ever crossed a time line? Jet lag, severe fatigue, is the result of a confused body clock.
This ‘body clock’ controls the rhythm of waking and sleeping. It is cued by external light, and bright lights can apparently reset the clock. Some doctors are using ‘light therapy’, shining bright lights on people for several hours before they want to wake up, to help people adapt to new time zones.
Many people with total blindness have life-long sleeping problems because their brains cannot be cued for sleep by light.
In Western Society, people are burning both ends of the candle at once. When sleep is so crucial for good health, it is worth investing in at least 8 hours of sleep each night.