Understanding the Stages of Sleep

Most of us might understand that sleep comes almost instantaneously with the mind shutting off and the body slipping into a deep slumber. The truth is that there is still a lot of activity going on inside the brain as we drift off. This brain activity marks different stages of sleep. Here’s what you need to know:

• At least 5 different stages of sleep have been identified so far.
• Sleep can be broadly classified into REM (Rapid eye movement) and NREM (non-rapid eye movement) sleep.
• Sleep follows a cyclical pattern with a different cycle beginning every 90 minutes.
• This cycle is: N1 > N2 > N3 > N4 > N3 > N2 > REM

What role does each state and stage of sleep play?

• The NREM sleep covers around 75% of the night.
• We enter NREM sleep as soon as we begin to fall asleep.
• NREM sleep has 4 stages.

Stages of NREM Sleep

Stage 1

• Occurs in the period between being awake and drifting off to sleep
• Characterized By: Light sleep

Stage 2

• Begins at the onset of sleep
• The mind disengages from the surroundings
• Breathing and heart rate are regular
• The body temperature drops

Stages 3 & 4

• Characterized by the deepest and most restorative sleep
• Blood pressure gradually drops
• Breathing becomes slower and more relaxed
• Muscles begin to relax and blood supply to the muscles increases
• Tissue growth and repair occurs
• Hormones are released
• Energy is restored

REM Sleep

• REM sleep occurs for the rest 25% of the night
• It starts about 90 minutes after falling asleep and like NREM, repeats every 90 minutes, gradually extending to longer periods as the night progresses.

REM Sleep:

• Provides energy to the brain and the body
• Influences performance during daytime

Also, the brain is in an active state and dreams occur during this cycle. The eyes move back and forth and the muscles are relaxed. The body becomes immobile.

Another important activity occurs in the levels of cortisol which dip during bed time and gradually increase as the night progresses to help improve alertness in the morning.