The Human Sleep Cycle – An Explanation of Sleep

Sleeping is something that everyone on the planet needs. While we sleep at varying times of the day and for varying lengths of time, it is still something that everyone must do to remain healthy both physically and mentally.

During the course of a night, a person goes through five different stages of sleep and goes through these five stages around four times a night. These stages are accompanied by body characteristics and brain wave activity. This activity is monitored in research labs with various pieces of equipment. An EEG (electroencephalograph) monitors brain wave activity, EKG (electrocardiograph) monitors heart activity, and EOG (electrooculograph) monitors eye movement. Researchers have in their use other monitoring technology as well, but for the purposes of understanding one night’s sleep, we’ll only need to use these three.

Before sleep begins the body is relaxed and is preparing itself for sleep, the EEG shows what is known as Alpha waves, constant up and down wave motions, coming from the brain. This is the time when we lay in bed and think about the day and gradually doze off to sleep. Once the sleep state is reached this is called stage one.

Stage One Sleep:

Theta waves are monitored on the EEG. Theta waves are relaxed wavelengths. These are accompanied by a relaxed heart rate, slower breathing rate, and a drop in body temperature. Stage one sleep lasts for only several minutes before the person passes into stage two sleep.

Stage Two Sleep:

Short bursts of brain wave activity are monitored via EEG that lasts for around twenty minutes before shifting into stages 3 and 4 sleep.

Stages 3 and 4 Sleep:

Delta wave activity is monitored via EEG. Both stage three and stage four sleep last for around 30 minutes together wherein a person is in a deep sleep. This is reflected by shallow breathing and complete relaxation of the body and muscles. Stage four is the last sleep stage before the stages reverse back toward stage one. From stage four a person goes back through stages 3, 2, 1, and then enters the next stage of sleep instead of waking.

REM (Rapid Eye Movement) Sleep:

REM sleep is a state of deep dream sleep experienced when stage one has been reached for the second time. Dreams during REM sleep are vivid, generally more so than dreams that occur at any other time during the night. During REM sleep the EEG records brainwaves that are similar to those of a waking person (Delta waves), the waves shown during REM sleep are Beta waves. These waves are accompanied by irregular pulse and breathing rhythms. Additionally, as the name REM suggests, the eyes also move rapidly under the eyelids.

After REM sleep the cycle starts again, but this time with REM sleep getting longer in length going from an initial ten minutes during the first sleep cycle to nearly 60 minutes before a person wakes up. Waking comes as stages three and four become shorter, and stages one and two become shallower. Sleep cycles run throughout the course of the night until the person awakens. As aforementioned, there are usually four full cycles before waking. Each person experiences these stages a little differently based on their age and sleeping routines, however, these stages are the basis of sleep and how it is experienced.