About Natural Sleep Cycles

Until recent history, it was long believed that the human brain shut down and did little to no functioning during sleep. Studies have shown, however, that this is far from true. The brain is involved during sleep and brain activity that happens during sleep is essential to health and general well being.

Significance

In a natural sleep cycle, there are five stages that occur. Each of these stages is characterized by different motions and brain wave patterns, as well as different levels of consciousness. Sleep is vital to human functioning, and each cycle helps the brain prepare for a new period of wakefulness. Natural and healthy sleep cycles are important for memory and concentration, as well as concentration, thought processing and overall functioning. Lack of natural sleep cycles affects mood and immune system functioning. If a person does not regularly complete natural sleep cycles, it will become more and more difficult to function in every day life.

Stage One

Stage one is the first stage in a natural sleep cycle. This refers to period of near-wakefulness, just after a person has fallen asleep. During this stage, a person will drift in and out of sleep. Their muscles will relax and breathing and heart rate will slow. It is easy to wake people up out of this stage of sleep. During this stage, it is also common for people to startle themselves awake after having the sensation that they are falling. This has to do with muscle relaxation and contraction typical of this stage. Stage one sleep, along with stages two, three and four, are together called non-REM sleep. A person will only experience one phase of stage one sleep per night, as opposed to the other stages, which repeat themselves several times.

Stage Two

After about ten minutes of stage one sleep, a person progresses into stage two. Stage two is a deeper sleep than stage one, but it is still not considered actual deep sleep. In this stage all eye movement stops and brain waves settle into a wave-like pattern. Brain waves will be in a lull, and then burst out with a few minutes of increased and rapid activity before drifting back into slow activity again. This pattern continues throughout stage two sleeping, along with a decreased heart rate and slight drop in body temperature.

Stages Three and Four

Stages three and four are called deep sleep, and they are difficult to distinguish because the differences are subtle. Stage four is more intense than stage three, but both are categorized by slow brain activity and no muscle movement. It is difficult to wake someone once they enter stage three and stage four sleep. Though it is during these stages that children will occasionally have night terrors, or frightening dreams that will wake a child up but that can not be remembered.

REM

Rapid Eye Movement (REM) is the last of the sleep stages, though not necessarily the last stage that a person will have in a night. REM sleep is characterized by brain activity that is similar to being awake. A person's eyes will move rapidly behind their eyelids, and breathing becomes more shallow and irregular. It is during REM sleep that most dreaming occurs, and if a person is woken out of an REM sleep stage, it is likely that they will be able to remember their dreams. Most people have three to five periods of REM sleep every night, with the first one usually happening about 90 minutes after first falling asleep. The sleep cycle naturally progresses in the following order: 1, 2, 3, 4, 3, 2, REM. Each cycle lasts anywhere from five to fifteen minutes but each stage of REM sleep will get progressively longer during the night.

Resources

• A resource on sleep cycles and sleep health.
• Information and tables on the activities during sleep stages.