The Sleep Cycle.

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There are five distinct stages in the sleep cycle.So,let us discuss the different stages of sleep in the cycle here:

Stage 1

This stage of sleep is considered as drowsiness. It is the transition stage from wakefulness to sleep. Within this stage, the sleeper’s eyes are closed with slower rolling movements, his/her respiratory rate will becomes more uniform. A person who is reading, watching television or attending an uninteresting lecture may fall to this stage accidently, or when the person is resting quietly. The person may undergo ‘hypnogogic experience’ during this period, which is dream –like sensations of falling, hearing sounds or seeing flashes of pictures. This stage is able to last from 5 to 10 minutes at the beginning of sleep, which is only around 5% of sleeping time in healthy adults.

Stage 2

The fast-frequent burst of activity (sleep spindles) is occurring in this stage. From stage 2 until stage 4, the muscle tension, heart beating rate and respiratory rate, including body temperature of the person who is sleeping will gradually decline and becomes even more regular. The person is even less aware of their surrounding although is still easily arousable here.

Stage 3&4

Stages 3 and 4 are considered as the slow-wave sleep, which are the deep sleep stage. Muscles of the person will relax further here, and the breathing is very regular. The deep sleep stage normally occurs 30 minutes after the person falling asleep, he/she is extremely difficult to be aroused now. Brain activity now is showing a slower and more regular pattern under EEG. The sleep cycle will go back to stage 2 after this stage and then enter the REM sleep finally. The electroencephalogram (EEG) is a device that frequently used to sense the electrical activity in the brain.It is used in the detection of the sleep stages by defining specific electrical patterns in the brain.

Stage 5

The EEG tracing of the stage is similar to the beta waves that observed during the person is awake. Brain-imaging study also shows that the neurons in cerebral cortex are more active at this stage. It is different from the other stages of sleep as the brain is very active although the sleeping person is not aware of their surroundings at all. The REM sleep has make up 20% of sleeping time as we will go through this sleep cycle 5-6 times within 8 hours of sleep. We will experience vivid dream during this stage. Although brief dream images can occur during other stage, most of the complicated, bizarre and plot-driven experiences most people think of as dream occur during this stage.

Reference:
Gokalp, G. (1999). Sleep and Dreams. Available: http://www.csun.edu/~vcpsy00h/students/dreams.htm. Last accessed 10th March 2013.