Sleep is triggered by a group of hormones in the body. These
hormones react to cues within the body and in the environment.
There is an approximate 80 percent of sleep time without dreams.
This stage of dreamless sleep is referred to as NREM which stands for
non-rapid eye movement. Dreams occur primarily during rapid eye
During non-rapid eye movement sleep or NREM, the breathing and
heart rates are slow and the blood pressure goes down. Based on the
Rechtschaffen and Kales standardization of the year 1968, NREM was
divided into 4 stages. However, it has been reduced to 3 by The
American Academy of Sleep Machine in 2007.
Stage 1 This stage mostly occurs in the start of sleep wherein theta
wave emerges while alpha waves vanish. Those who are aroused from
this stage believe that they have been completely awake. It is also in
this stage when the body experiences hypnic jerks.
Stage 2 In this stage, dreaming is rare and no eye movement takes
place. The sleeper may also be wakened easily.
Stage 3 This is also referred to as slow-wave sleep of SWS, wherein
deep sleep takes place. This is also the stage when dreaming occurs.
However, the content of slow-wave sleep is likely to be less
memorable, less vivid and disconnected than those in rapid eye
On the other hand, rapid eye movement sleep also known as REM, is
a normal phase of sleep making up between20% and 25% of the
whole sleep time. Apart from the swift movement of the eyes, this
stage is also characterized by low muscle tone.
Human beings usually experience 4 to 5 REM sleep periods during a
usual full session of sleep, and the last is longer than the first one.
According to sleep experts, the brain neurons are as dynamic during
rapid eye movement sleep as they are when the body is awake.
However, atonia, a relaxed state of the skeletal muscles, makes the
body paralyzed during REM.
In the succeeding posts, you will know more about sleep and how
to make the most out of it.
