While we sleep, there are different sensations that are occurring throughout our bodies. Our bodies cycle through four different stages while we sleep. The stages of sleep are classified as Non-Rapid Eye Movement sleep (NREM) and Rapid Eye Movement sleep (REM). The four Stages of sleep are as follows:
- Stage 1: This is the stage when our bodies are transitioning between sleep and conscious thought. The human body also transitions between synchronized and unsynchronized brainwaves during this time. This period usually lasts 7 to 11 minutes, and varies depending on how tired that person is. Someone who is exhausted may only enter this stage for 1 to 2 minutes before going into stage 2. It is very common for people to experience involuntary muscle contractions during this stage.
- Stage 2: Heart rate begins to slow down significantly and the temperature of the body drops 2 to 3 degrees. Brain wave activity begins to during change during this stage as well. Our brains begin to have short busrts of brain waves called sleep spindles. This is when we also become completely disengaged from what surrounds us.
- Stage 3: Sleep researchers have found that this is the most vital stage of sleep that is required by our bodies. Stage 3 is considered the deepest, most rejuvenating form of sleep. Brain waves are at their slowest during stage 3, and they are referred to as delta waves. Our blood pressure drops sharply, which helps regulate our blood pressure when we are awake. Tissue and cell repair happens along with muscle growth. Those who excercise experience the neccessary growth and repair of their muscles because large amounts of Human Growth Hormone (HGH) are secreted during this time. The energy needed for physical movement and cognitive function is restored. Sleep deprivation takes such a harsh toll on the body because of a lack of stage 3 sleep.
- Stage 4 Rapid Eye Movement : Each stage of sleep has its own purpose that it serves, but the most perplexing of them all is REM sleep. All mammals experience some form of Rapid Eye Movement sleep, although the amount of time they spend in REM sleep varies. During this stage, the brain is active and Rapid Eye Movement (REM) occurs. The eyes rapidly dart back and forth in all directions during this stage. This cycle happens about every 90 minutes. Most dreaming occurs during this stage as well. As adults, this makes up about 20 to 25% of our sleep. Scientists are still unsure on what purpose this stage of sleep serves. The reason is because there are no detrimental effects that result from a lack of Rapid Eye Movement sleep. In a clinical study conducted by the National Center of Biotechnology information, researchers found out that people with depression actually felt happier when they stopped experiencing REM sleep cycles.