Alright, so as promised from the previous post, here are the stages of sleep, which are divided into five distinct stages.
Stage 1 – Theta Waves
Theta waves mark the moment where a “sensory curtain” drops and isolates the mind from the outside world. At this stage, you no longer hear outside noises, smell outside smells, or feel the very mattress you’re sleeping on. Stage 1 is a light sleep, however a loud enough noise will still awaken you, and upon awakening you would think that you weren’t even asleep at all. However, during this stage, you wouldn’t wake up if someone whispered your name because your brain is still fairly closed off to the outside world. At this stage, the eyes make slow back-and-forth movements. This stage lasts around 5 minutes.
Stage 2 – Sleep Spindles & K Complexes
Stage 2 is a deeper sleep than stage 1, yet waking up from this stage would still be relatively easy. Stage 2 sleep contain two sleep specific brainwaves called “sleep spindles” and “K-complexes,” which are very short bursts of wave activity lasting only two to three seconds. (See: image below) So on an EEG machine, sleep spindles look like a “spindle” on an old spinning wheel, and K-complexes are large waves that appear to spike and come out of nowhere. These short bursts of activity represent with certainty that the individual is indeed asleep. This stage lasts for 5 to 10 minutes.
Stage 3 – Delta Waves
Stage 3 sleep is the first stage of “deep sleep.” At this stage the waves are deeper and more pronounced than the stage 2 brainwaves. You can think of stage 2 waves as like small, boring waves at the beach — great for swimming but not much else, and stage 3 waves are like massive swells that come when there’s a storm — great for surfing. Sleep spindles and K-complexes are still present in stage 3.
Stage 4 – Delta Waves
When the sleep spindles and K-complexes are no longer detectable, the sleeper has entered the deepest stage of sleep, stage 4. This is also known as “slow-wave” sleep. At this stage it’s very difficult to wake up, the heart rate and breathing are regular and slow, and the muscles are completely relaxed. During this stage of deep sleep the body secretes growth hormone, which helps cells divide and multiply and build new tissue.
Stage 5 – REM Sleep
Soon after stage 4, you enter a somewhat lighter stage of sleep again and the sleep spindles and K-complexes of stage 3 reappear, which will last about 10 minutes or so, and then the eyes begin to jerk back and forth. Brain activity increases greatly at this point, and all voluntary muscles become paralyzed. This period of sleep is called REM sleep, and is the stage where we are dreaming. REM stands for “rapid eye movement.” The first period of REM sleep will usually last only about 10 minutes, and throughout the night move between deep and shallow sleep, alternating between REM and non-REM sleep, with the second half of the night being more dream-rich.
photo credit: alleydog.com