The Various Stages of Sleep and their Significance

Sleep is one of the most important factors for good health. When we sleep, our bodies use this down time to grow bones, repair muscles, sort memories and manage our hormones.

Each stage of sleep serves an important purpose and plays a distinct role in maintaining our brain's overall cognitive performance. Some stages are linked to physical repairs that keep you healthy and ready for the next day. The entire sleep cycle repeats itself multiple times a night. This article discusses the stages of sleep and explains what happens during each stage.

What happens in the brain during sleep?

Brain chemicals play an important role in our sleep cycle. Neurotransmitters allow neurons to communicate with one another. They regulate whether we are awake or asleep based on which neurons they act on. Neurons in the brainstem produce neurotransmitters called serotonin and norepinephrine that chemicals keep our brain active when we’re awake. Neurons located at the base of the brain are responsible for us falling asleep by producing a neurotransmitter called melatonin.

During periods of sleep, our brain goes through natural activity cycles. We have four stages of sleep in all across two phases:

The first phase is non-rapid eye movement (NREM) and is divided into three stages. During the later stages of this phase we experience deep sleep. The second phase is REM sleep and it occurs between an hour and an hour and a half after falling asleep. REM sleep is characterised by vivid dreams. Our body alternates a few times between non-REM and REM stages during our sleep.

What is Non-REM sleep?

Stage 1:

In this stage we are in a light state of sleep that lasts for 5 to 10 minutes. Everything, including our eye movement and muscle activity, begins to slow down.

Our eyes are closed in this stage and if we are ‘woken up’ during this stage then it would appear as if we haven't slept at all. This is the stage where we sometimes experience a sensation that is like we are about to fall and then experience a jerk/ muscle contraction. This movement is referred to as hypnic myoclonic or hypnic jerk by medical professionals.

Stage 2:

This second stage of light sleep includes intervals of muscular tone (partially contracting muscles) alternating with periods of muscle relaxation. Our eye movement ceases, our heart rate lowers, and your body temperature drops and brain waves slow down. Your body is preparing to go into deep slumber.

Stage 3:

In this stage we enter into a deep sleep. During this period, our brain generates delta waves, which are waves of very low frequencies. We do not exhibit any eye movement or muscle activity. You won't wake up very easily in this stage and if woken up you may feel disoriented and groggy.

What is REM Sleep?

When the body enters REM sleep, activities in the brain increase, indicating that we are not in a deep state of sleep. These activity levels are comparable to when you are awake. As a result, REM sleep is the stage during which you will have vivid dreams. Conversely, we are unable to voluntarily move muscles. You enter the REM stage within 60-90 mins. Spending about 20-25% of your time asleep in the REM stage is a good goal.

The amount of REM sleep one experiences is inversely proportional to one's age.

People who don’t get enough sleep are at higher risk for developing various health conditions including obesity, diabetes and heart problems.