A resource from the Division of Sleep Medicine at Harvard Medical School
Stage One: This is the relatively light stage of sleep in which one is shifting from being awake to being asleep. Muscle activity begins to slow but one could be woken up easily. This stage is very short, lasting only a few minutes. During this period unexpected muscle contractions are common (this often happens after one experiences a falling sensation).
Stage Two: Stage two is when the sleeper becomes disconnected from their surrounding environment and their body temperature drops. This stage lasts about 20 minutes.
Stage Three and Stage Four: Both stages three and four are considered the deepest stages of sleep and they are often grouped together because of their similar characteristics. It is very hard to wake someone from these stages of sleep. No muscle movement or eye motion occurs during stages three and four. Blood pressure drops, breathing and heart rate slows, hormones are discharged, and energy is replenished. Delta waves, the slowest brain waves, are associated with these stages. They are present in stage three but almost the only waves produced during stage four. This sleep, also known as delta sleep, is comparable to a coma; except, of course, one wakes up.
Stage Five: This is the stage of REM sleep (stages one through four fall under NREM). It is called rapid eye movement sleep because the eyes dart about; one can see this if they watch someone in this stage. The eyes are moving back and forth like this because dreaming occurs in stage five and the brain is highly active. Along with the higher brain activity, both heart rate and breathing accelerate. This stage is also called paradoxical sleep because ironically, our body is totally immobile, while our mind and other organs are super active. The body is essentially paralyzed during stage five. Muscles are motionless due to the amino acid glycine, which is released in this stage. Luckily this paralysis occurs, or else we would most likely act out our dreams and probably get injured and/or injure others and/or property quite often.
Stage One: This is the relatively light stage of sleep in which one is shifting from being awake to being asleep. Muscle activity begins to slow but one could be woken up easily. This stage is very short, lasting only a few minutes. During this period unexpected muscle contractions are common (this often happens after one experiences a falling sensation).
Stage Two: Stage two is when the sleeper becomes disconnected from their surrounding environment and their body temperature drops. This stage lasts about 20 minutes.
Stage Three and Stage Four: Both stages three and four are considered the deepest stages of sleep and they are often grouped together because of their similar characteristics. It is very hard to wake someone from these stages of sleep. No muscle movement or eye motion occurs during stages three and four. Blood pressure drops, breathing and heart rate slows, hormones are discharged, and energy is replenished. Delta waves, the slowest brain waves, are associated with these stages. They are present in stage three but almost the only waves produced during stage four. This sleep, also known as delta sleep, is comparable to a coma; except, of course, one wakes up.
Stage Five: This is the stage of REM sleep (stages one through four fall under NREM). It is called rapid eye movement sleep because the eyes dart about; one can see this if they watch someone in this stage. The eyes are moving back and forth like this because dreaming occurs in stage five and the brain is highly active. Along with the higher brain activity, both heart rate and breathing accelerate. This stage is also called paradoxical sleep because ironically, our body is totally immobile, while our mind and other organs are super active. The body is essentially paralyzed during stage five. Muscles are motionless due to the amino acid glycine, which is released in this stage. Luckily this paralysis occurs, or else we would most likely act out our dreams and probably get injured and/or injure others and/or property quite often.
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| Above is an electroencephalograph (EEG) that shows the differences in brain frequencies during the various stages of sleep. (Image via The University of Alabama's States of Consciousness: Sleep and Dreams) |
Works Cited:
“Stages of Sleep.” National Sleep Foundation. Sleepdex – Resources for Better Sleep. n.p. n.d. Web. 24 Jan. 2012. <http://www.sleepdex.org/stages.htm>.
“Different Stages of Sleep.” Oracle ThinkQuest Education Foundation. ThinkQuest Team C005545, 2000. Web. 24 Jan. 2012. <http://library.thinkquest.org/C005545/english/sleep/stage.htm>.
“What Happens When You Sleep?” National Sleep Foundation. National Sleep Foundation, 2011. Web. 24 Jan. 2012. <http://www.sleepfoundation.org/article/how-sleep-works/what-happens-when-you-sleep>.
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