Stages of Sleep

Art & Research: Xiaoying Wu

Further Reading Literature: Xiaoying Wu

Stages of Sleep

When we close our eyes to sleep for the night, we realize the next moment, we’re awake. What we do not realize is that our body just cycled through four stages of sleep called N1, N2, N3, and R (NCBI). Stages N1, N2, and N3 are part of the non-REM sleep stages, while the R stage is REM sleep. Non-REM stands for non-rapid eye movement, and REM stands for rapid eye movement (NCBI). Through the night, our body cycles through these four stages; After the R stage, our body usually goes back to the N1 stage and cycles through again until we wake up (American Sleep Association).

Stage 1: N1 (NON-REM)

The N1 stage is the transition from wakefulness to sleep (NINDS). People are easily woken up in this state. Alpha waves and theta waves are produced in the brain, which are low frequency waves that cause relaxation and drowsiness (NCBI). The brain waves, heartbeat, breathing, and eye movement begin to slow down (NINDS). Some people may experience sudden muscle contractions in this stage (American Sleep Association).

Stage 2: N2 (NON-REM)

The N2 stage is a period of light sleep where theta waves begin to appear (NINDS). There are bursts in brain activity called sleep spindles, and K-complexes appear to signify transition to deeper sleep (NCBI). K-complexes are large brain waves that help with arousal to maintain sleep (NCBI). Heart rate and breathing slows down more (NINDS). The body’s temperature lowers and eye movement stops (NINDS).

Stage 3: N3 (Non-REM)

The N3 stage is when deep sleep occurs (NINDS). Slow waves called delta waves increase in the brain, making it difficult to wake up the person (American Sleep Association). Heart rate and breathing reaches its lowest in this stage, and the muscles become fully relaxed (NINDS).

Stage 4: R (REM)

The R stage is the REM period where dreams occur (NCBI). This stage is important for memory skills as it stimulates the brain to send signals to the thalamus, then to the cerebral cortex; the cerebral cortex is the brain region responsible for “learning, thinking, and organizing information” (UPMC). As indicated in the name, rapid eye movement (REM), the eyes rapidly move during this sleep stage. Heart rate and breathing increases, while the limb muscles become temporarily paralyzed (NINDS).

The importance of sleep

During sleep, our body grows/recovers by producing and breaking down proteins (American Sleep Association). Adults should be getting 7-9 hours of sleep per night (American Sleep Association). Make sure you are getting the sufficient amount of sleep every night to properly recover from your day of work!

Want to learn more about this topic?

Check out the additional resources below!