The two basic distinctions that apply to sleep are NREM or non-rapid eye movement and REM or rapid eye movement. In the duration of one night they occur as a 90-minute cycle, repeating up to six times for the duration of the night in all four stages of NREM and REM. REM results from NREM.

Sleep Cycle

Four stages in a duration of almost 90-120 minutes makes one sleep cycle. Dreams are common to all stages with the most vivid and memorable in the last stage, the common term for which is REM sleep. The sleep cycle is repeated four to five times a night, sometimes going up to seven. This is the reason for many different dreams in one night. Usually the ones in the last stage prior to waking up are the ones recalled. Not being able to remember the others does not rule out their occurrence. Many are insistent about not dreaming when the truth is that they simply don t remember doing so.

The Stages Of Sleep

On falling asleep, the transition sleep or stage 1 begins, progressing a few minutes later to stage 2 of baseline sleep. This is the stage leading to the other three and accounts for nearly 50-65% of sleep time. Another 15-20 minutes later, it reaches stage 3, followed by stage 4, referred to as delta sleep or slow wave sleep due to the very high voltage slow brain waves. Delta sleep has a lot in common to a coma, apart from being reversible. During the first four stages, a reduction takes place in respiration and heart rate with the body relatively immobile. After 30 minutes or so of slow wave sleep, there is a sudden lightening into stage 2, rapidly followed by a very active brain wave pattern called paradoxical or REM sleep. At the same time, respiration and heart rate accelerate with loss of postural and skeletal muscle control. Brain activation occurs simultaneously causing hallucinations and dreams.

NREM

In stages 1,2 and 3, it is NREM or non-rapid eye movement sleep, when dreams are not as vivid and eyes move. This inactive stage of sleep makes up 97% of sleep, with only 6% who awaken in NREM being able to recollect their dreams. NREM accounts for 78% of sleep.

REM

During REM or rapid eye movement, eyes move to and fro under closed eyelids. REM occurs in stage 4, for as long as one hour, repeating at 90 to 100 minute intervals, three or four times a night. REM increases brain temperature and makes breathing and heartbeat irregular. Blood flow is increased as well. Most awakening in REM recall dreams vividly due to the brain being very active.

REM sleep is considered important for memory and learning. The hypothesis for sleep in general and REM in particular, is of restorative nature. Loss of REM sleep causes irritability, anxiety and depression. Many lapse into REM rebound when REM sleep is insufficient. Therefore REM sleep periods are more frequent in occurrence with a longer than average duration.

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Dr. Richard Waller has been helping thousands of infetile couples and gave hope to childless women since 1999 through the process of In-vitro fertilization. He is based in England. please visit http://www.biology-online.org