Until the 1950s, most people thought of sleep as a passive process, whose primary function is to restore our energy balance.
Today we already know that our brain is very active during sleep. Moreover, sleep affects in many ways both our physical and mental health.
If we need to define sleep - it's a natural recurring state of mind, characterized by altered consciousness, suppressing of nearly all voluntary muscles and significantly reducing our interaction with the environment.
The decreased ability to react to stimuli distinguishes sleep from quiet wakefulness.
Experts psychologists would say that dreams are only the realisation of all our fantasies. Sleep is the time when our mind works in pursuit of our aspirations and make them come true through the prosess of dreaming.
Nerve signals
Nerve signals called neurotransmitters control waking and our sleep cycles, by affecting different groups of nerve cells in the brain. Neurons in the brainstem connect the brain with the spinal cord and produce serotonin and norepinephrine which keep some parts of the brain active while we are awake. Other neurons at the base of the brain send signals when we fall asleep. These neurons appear to "exclude" the signals that keep us awake. Studies show that when we are awake, a chemical substance called adenosine accumulates in our blood and causes drowsiness. And vice versa - while we sleep, concentration of adenosine reduces and we gradually refresh.
Stages of sleep
During sleep, we usually pass through five phases of sleep: stages 1, 2, 3, 4, and REM (rapid eye movement) sleep. These stages progress in a cycle from stage 1 to REM sleep, then the cycle starts over again with stage 1. We spend almost 50 percent of our total sleep time in stage 2 sleep, about 20 percent in REM sleep, and the remaining 30 percent in the other stages. Infants, by contrast, spend about half of their sleep time in REM sleep.
Stege 1
The sleep is light and we can be awakened easily. Our eyes move very slowly and muscle activity slows. People awakened from stage 1 sleep often remember fragmented visual images. Many also experience sudden muscle contractions, often preceded by a sensation of starting to fall. These sudden movements are similar to the “jump” we make when startled.
Stage 2
Our eye movements stop and our brain waves (fluctuations of electrical activity that can be measured by electrodes) become slower, with occasional bursts of rapid waves. Our heart rate slows down and body temperature drops.
Stage 3
Extremely slow brain waves called delta waves begin to appear, interspersed with smaller, faster waves.
Stage 4
The brain produces delta waves almost exclusively. It is very difficult to wake someone during stages 3 and 4, which together are called deep sleep. There is no eye movement or muscle activity. People awakened during deep sleep do not adjust immediately and often feel groggy and disoriented for several minutes after they wake up.
REM sleep
Our breathing becomes more rapid, irregular, and shallow, our eyes jerk rapidly in various directions, and our limb muscles become temporarily paralyzed. Our heart rate increases, our blood pressure rises. People tend to have clear dreams during that phase.
How many hours of sleep do we need?
The amount of sleep each person needs depends on many factors, including age. Infants generally require about 16 hours a day, while teenagers need about 9 hours on average. For most adults, 7 to 8 hours a night appears to be the best amount of sleep. Women in the first 3 months of pregnancy often need several more hours of sleep than usual. The amount of sleep a person needs also increases if he or she has been deprived of sleep in previous days. Getting too little sleep creates a “sleep debt,” which is much like being overdrawn at a bank. Eventually, your body will demand that the debt be repaid.
We don’t seem to adapt to getting less sleep than we need, but we can get used to a sleep schedule. The best way to understand whether you had enough sleep is to assess the level of drowsiness. Do you consider yourself exhausted at work or while watching TV? If so, you are not getting enough sleep at night! That is why it is important to create healthy sleep habits and have a comfortable and relaxing mattress.
Who knows, maybe dream and love are one and the same thing? - Jonathan Coe
The best way to make your dreams come true is to wake up. - Mohammed Ali