Just like we need water and food to survive, we also need sleep. Sleep is heavily influenced by circadian rhythms, and hormonal/environmental factors as well. It is a restorative process that gives us energy for the day ahead of us. It gives the body a chance to repair muscles and other tissues and gives the brain a chance to organize and archive your memories.
When we see someone sleeping, we recognize the following characteristics; the person's eyes are closed, the person doesn't hear anything unless it's a loud noise, their breathing is in a slow, rhythmic pattern, the persons muscles are completely relaxed, and their heart rate slows down.1 The person also occasionally rearranges their body--this happens approximately once or twice an hour, it is the body's way of making sure no part of the body is denied oxygen.
There are different stages of sleep, and about every 90 minutes we pass through a cycle of five distinct sleep stages.
We can see what stage of sleep a person is by connecting an EEG to their head. The electrodes pick up weak electrical signals from the brain, eye and facial muscles. Each stage of sleep is characterized by different brainwaves.2 For example, alpha waves are the major rhythm seen in normal relaxed adults, while stage 4 of sleep emits delta waves, which are the lowest frequency and occur during deep sleep.
The fifth stage of sleep is REM sleep, which is short for rapid eye movement. REM sleep occurs at several points during the night. Most people experience three to five intervals of REM sleep per night. During REM sleep brainwaves speed up to awake levels. An average person will spend twenty five percent of the night in REM sleep.3 REM sleep is when dreaming occurs. Dreaming...