Stages of Sleep Explained: How Brain Hormones Control Your Sleep

By Regina Bailey January 27, 2020

Sleep is a state of decreased responsiveness to stimuli and reduced activity that can be easily reversed. Although we are unconscious during this activity, sleep is an important means for our bodies to recuperate, conserve energy, and form memories. There are four stages of sleep, which can be grouped into two broad categories: rapid eye movement (REM) and non-REM sleep. Non-REM sleep is subdivided into three stages. All four stages of sleep reoccur throughout the duration of the sleep cycle and each fulfills important functions.

Key Takeaways: Stages of Sleep

• Sleep is comprised of four stages (N1, N2, N3 and REM) in two categories (non-REM and REM sleep).
• The hypothalamus is the major driving force for wakefulness and sleep through circadian rhythm and sleep homeostasis.
• Non-REM sleep is a progression from the lightest to the deepest stage of sleep with slowing of heart rate, blood pressure, respiratory rate, and muscle activity.
• REM sleep is a more active stage of sleep associated with dreams and faster brain wave activity.
• Tips for improving your sleep include setting a schedule, avoiding stimulating activities near bedtime, performing relaxation techniques before bed, and exercising regularly during the day. 
  

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My Take -  I've added some of this to my Shall Every Knee Bow annual piece saying: 

I defy anyone to explain evolution and the existence of that amazing biological complexity known as the human four stage sleep cycle, requiring a fully developed brain, with fully developed harmonious chemistry.

The human sleep cycle requires use of "the thalamus, hypothalamus, basal forebrain, pineal gland, and portions of the brainstem", and requires "neurotransmitters GABA and adenosine, sunlight working in conjunction with the circadian clock, and "hormones such as glutamate, histamine, and orexin" as the chemistry to make it all work.  How could that all happen progressively?  So, how could anyone sleep if this system wasn't completely in place from the beginning?