Sleep Stages and Sleep Cycles

Sleep Stages

There are five stages of sleep. Scientists categorized the stages of sleep based on the characteristics of the brain and body during sleep. Stage 1, 2, 3, and 4 are categorized as ‘non-REM sleep’, and the fifth stage, is REM sleep.

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Stage 1 Sleep

Initial light sleep, individuals are easily awoken during this stage.

Stage 2 Sleep

A deeper sleep where the body temperature starts to drop and heart rate slows, decreasing blood pressure.

Stage 3 and 4 Sleep

Deepest sleep of all the stages. Human Growth Hormone is produced and released into the body resulting in repair and rejuvenation. The body repairs and restores tissues, muscles, bones and the immune system. Neurotransmitters are produced for nerve and brain function. Hormone are produced for regulatory processes. Reduces The need for sleep and is the most restorative stage.

Stage 5 Sleep

REM Sleep (rapid eye movement) occurs. Consolidation and organization of thoughts for memory and behavioral responses.


Sleep Cycles

During sleep the body repeats the 5 stages of sleep in what is called a cycle. If uninterrupted, the body will go through 4-5 cycles in approximately 7.5 hours. Each cycle the sleep stages vary in length. It is during the 3rd and 4th cycles that the 3rd and 4th stages are the longest. As mentioned above these stages are the most restorative and crucial for maintaining or improving one’s health. When there is an interruption the cycles will restart, they are not cumulative. These interruptions can occur many times a night resulting in poor sleep and the inability to restore the mind and body. The stages and cycles collectively are known as “Sleep Architecture”.

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