The Sleep Cycles: Why Your Brain Needs Rest in Order to Reset

As a human being, you are an intricate ensemble of entwined systems that rely on sleep cycles in order to function properly. Like components within complex machinery, your body and brain require significant downtime for “maintenance” that enables their optimal performance. Sleep is a crucial biological intermission wherein this upkeep takes place, and it must occur in order for the show to go on.

There are five sleep stages which occur in succession several times throughout the night, repeating roughly every 90 minutes or so. The most obvious distinction between them is that the first four are non-REM (Rapid Eye Movement) sleep, while the fifth phase is the definitive REM state. Regardless, all are critical to the well-being of your respiratory, digestive, endocrine, immune and central nervous systems.

Drifting Off

This transitional phase of sleep is relatively short, lasting anywhere from 5 to 10 minutes. As your heart rate, breathing and muscle activity slows down, your brain enters what is known as Alpha state, then slips into Theta state. This initial part of the sleep cycle is often accompanied by muscle spasms and/or a sense of falling known as hypnic myoclonia — thus the term “falling asleep.”

A Light Snooze

Nearly half of your time asleep is spent in this state, as your heart rate and core body temperature continue to decrease. This phase triggers what is known as the body’s Circadian rhythm sleep cycle, which determines when and for how long you will sleep.

Double Deep Sleep Cycles

Sleep stages three and four are extensions of one another, distinguished by core body temperature that can dip as low as one degree below normal — down to 97.6 degrees or so. These periods of deep sleep are when your brain wave activity slows down to the Delta frequency — meaning that you are in the phases of sleep that are the most difficult to awaken from.

Muscle spasms and general mobility tend to cease here, and although this is an NREM state of sleep it is often distinguished by nightmares and bedwetting in children as well as sleepwalking in adults. During these stages, your brain releases human growth hormone which increases blood flow to your dense tissues and extremities.

This serves to repair muscles and joints that are exerted throughout the day. Meanwhile, the release of additional hormones called leptin and ghrelin regulate the hunger cravings you’ll experience the following day so that you don’t over-eat.

Cue the Music

The final stage of your sleep cycle is known as the REM phase, wherein your brain waves spike to near-waking levels of activity. Here, your brain begins to re-energize itself and your body with a high degree of neuroactivity.

Most dreaming occurs during phase five, as your eyes oscillate back and forth behind your eyelids. During REM sleep, however, your body stays immobile due to your brain’s release of glycine and gamma-aminobutyric acid (GABA) that “paralyze” your skeletal muscles so that you do not act out your dreams.

After spending 20% or more of your time in this phase, your sleep cycle either resets or you wake up as your body temperature returns to its normal level of 98.6 degrees.

Benefits of Monitoring Your Sleep Patterns

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Originally published at on October 26, 2017.

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