The Science of Sleep
To gain a better understanding of sleep disorders, it helps to understand the basic science behind sleep and terms that you may encounter on your path to diagnosis and resolution of your sleep problems. Neurotransmitters are nerve-signalling chemicals that control whether we are asleep or awake by acting on different groups of nerve cells (neurons) in the brain. Neurons located in the brainstem produce neurotransmitters such as serotonin and norepinephrine that keep some parts of the brain active while we are awake. Other neurons at the base of the brain begin signalling as we fall asleep.
Stages of Sleep
A sleep cycle is classified by three stages of non-rapid eye movement (NREM) sleep followed by a period of rapid eye movement (REM) sleep.
During stage 1, which has a duration of 5 to 10 minutes, the level of sleep is relatively light, and is often considered a transition period between wakefulness and sleep. During this stage, the brain produces high amplitude theta waves, which are very slow brain waves. If you awaken someone during this stage, they may not even realize they were asleep.
Stage 2 lasts for about 20 minutes, during which, the brain begins to produce bursts of rapid, rhythmic brain wave activity known as sleep spindles. The body temperature starts to decrease and heart rate begins to slow.
During this stage, also known as the delta stage, deep, slow brain waves called delta waves begin to emerge. Some people do not respond to environmental noises and activity during this period. This stage is a transitional period between light sleep and a very deep sleep. Nocturnal activities such as bedwetting and sleepwalking more likely occur towards the end of this stage of sleep.
Most dreaming occurs during the fourth stage of sleep, known as REM sleep. REM sleep is characterized by rapid eye movement, increased respiration rate, and intensified brain activity. REM sleep is also referred to as paradoxical sleep because while the brain and other body systems get more active, the muscles become less active and more relaxed.