Common opinion of people prior to the first half of 20th century was an idea of sleep as a useless part of our daily lives. Modern science tells us that our brain is actually very active during sleep. In addition, the amount of sleep we have reflects on our daily functionality and our mental and physical wellbeing in many ways that we are just beginning to uncover. Chemicals in our brain called neurotransmitters control whether we are asleep or awake.
These chemicals act on different groups of nerve cells, or neurons, in the brain. Connecting the brain with the spinal cord, neurons in the brainstem produce neurotransmitters such as serotonin and norepinephrine. Both of these chemicals maintain certain parts of the brain active while we are awake. There are other neurons at the base of the brain making signals when we fall asleep. These neurons behave like a turned-off switch keeping us awake. Additional research also revealed that a chemical called adenosine builds up in our blood while we are awake and causes drowsiness. Fortunately, this chemical gradually decreases during our sleep.
Stage 1 is light sleep. We are able to drift in and out of sleep and can awake easily. Our muscle activity slows, as well as our eyes who move very slowly. Stage 1 sleep allows people become awakened and often remembering visual images from their dreams. Some people also experience unexpected muscle contractions, called hypnic myoclonia. Those contractions often associated with a dream or sensation of falling from different structures. These movements are similar to the “jump” we make when startled.
Stage 2 sleep usually associated with stopped eye movements. Measured by electroencephalographs, our brain waves (fluctuations of electrical activity) become slower, with accidental bursts of rapid waves called sleep spindles.
Stage 3 demonstrates extremely slow brain waves called delta waves beginning to appear, mixed with smaller, faster waves.
Stage 4 of sleep produces almost exclusively delta waves. To wake someone during stages 3 and 4 becomes very difficult. These stages combined are also known as a deep sleep. You do not see eye movement, nor muscle activity. Awakened during deep sleep, people have a problem of immediate adjustment. The often feel dizzy and disoriented for a few minutes after they wake up. Some children experience bedwetting, nightmares, or sleepwalking during deep sleep.
The most unusual portion during our sleep is a REM sleep. It could be identified by our breathing, which becomes more irregular, rapid, and shallow. Our eyes moves rapidly in various directions, with our limb muscles staying temporarily immobilized. During REM sleep the heart rate increases and blood pressure rises. Some males develop penile erections. Awakening during REM sleep often allows to describe recent dreams, mostly illogical and bizarre.
REM sleep happens several times during the night. It is usually related to dreams people see. However, if we are not awakened immediately after the REM sleep, we do not remember those dreams. The first REM sleep period usually happens between 70 to 90 minutes after we fall asleep. In average, a full sleep cycle normally takes 90 to 110 minutes. The first sleep cycle consists of relatively short REM periods with a long period of deep sleep. After the first sleep cycle is over, the REM sleep periods have tendency to be increasing in length. Deep sleep cycle is decreasing. By the morning, our sleep time is slowing down towards Stages 1, 2, and REM.
It is normal for people, being awakened soon after sleeping for a few minutes, become unable to recall the last things before they fell asleep. It is a so-called form of amnesia is common for people often forgetting their telephone calls they have had in the middle of the night. Now we can explain why most of the time we don’t remember our alarm clocks ringing in the morning when we are going right back to sleep after turning them off.