The Sleep Architecture - Stages of Sleep

We all need good night sleep, although there are varying differences with circadian rhythms and sleep styles to be energetic, to be alert, and to stay healthy.

Sleep is made up of distinct stages with certain characteristics defined by brain waves, eye movements, and muscle tension.

In a sleep lab, electroencephalography (EEG), electro-oculography (EOG), and electromyography (EMG) are used to record these stages. The two broad categories of sleep include:

• Rapid eye movement (REM) sleep
• Non-rapid eye movement (NREM) sleep

REM Sleep

There are small, variable-speed brain waves, rapid eye movements like those of eyes open wakefulness, and no muscle tension during REM sleep. It is during REM sleep that you have most of your dreams. You may have a recall of vivid imagery when you wake up from REM sleep.

NREM sleep is composed of four different levels or stages - 1, 2, 3, and 4, which are characterized by different combinations of brain waves, eye movements, and reduced but not absent muscle tension. Different stages of sleep include:

• Stage 1 - light sleep
• Stage 2 - moderate sleep
• Stages 3 and 4 - deep or delta sleep

Delta Sleep or Deep Sleep

The amount of delta sleep you get each night reflects your sleep intensity or quality. Delta sleep is the deepest level of sleep, a regenerative period during which your body heals itself.

During delta sleep, the growth hormone secretion is highest and some researchers believe that this is significant for growth and repair of body tissue.

It is mostly during first third of the night, Delta sleep takes place and it makes up about 10 to 20% of total nighttime sleep in normal young adults. It is mostly during the last third of your night’s sleep that REM sleep takes place and it comprises usually 25 % of the sleep period.

A person’s age, amount of prior sleep and various diseases has an effect on Delta sleep. As a rule, delta sleep decreases with age and may be brief in healthy, elderly males. If you do not get enough delta sleep, you will feel tired and groggy the next day.

Elderly people have smaller proportions of delta sleep, which is why they can be easily aroused by environmental noise.

Medical problems such as obstructive sleep apnea, periodic leg movements during sleep, or fibromyalgia may affect both the quantity and the quality of delta sleep. This, in turn, probably accounts for the feeling of fatigue experienced by people suffering from these ailments.

Of course, young children have particularly large proportions of delta sleep, which increases if they are sleep deprived. This is the reason why it is difficult to wake up a young child.