Human sleep is characterized by 5 stages.Stages 1 through 4 involve non-rapid eye movement sleep , followed by stage 5 or rapid-eye movement sleep (REM sleep). An adult cycle requires approximately 90 minutes; a baby’s sleep cycle takes about 60 minutes. The above graph shows an average cycle in an 8-hour block
Sleep Cycle Stages
Stage 1 Sleep: Very shallow , superficial sleep . Eyes move slowly and little muscle activity occurs. Stage 1 sleep is fragmented and waking up occurs easily, it is not restorative or refreshing.c
Stage 2 Sleep: Usually the longest stage of sleep. Eye movements slow down but awakening can still occur easily.Older individuals and those with chronic illness may spend most of the night in stage 2 sleep.
Stage 3 Sleep: The beginning ofslow wave sleep.Many of the body’s repair processesoccur during this deeper stage of sleep. More difficult to wake up: awakening may result in a confused,disoriented feeling.
Stage 4 Sleep: The deepest stage of NonREM sleep. Neurotransmitters and growth hormones are synthesized. Slow wave sleep is most prominent and intense during childhood and declines sharpely at puberty and across the second and third decades of life.Beyond age 30 there is a progressive decline in slow-wave , deep sleep. Slow wave sleep may be completely absent in old age.
Stage 5 Sleep or REM Sleep: (Rapid Eye Movement)-Most dreaming occurs.Breathing becomes more shallow,rapid , and irregular.blood pressure and pulse rise: oxygen consumption increases: blood flow to the brain increases. Eyes move in a jerking manner but muscle paralysis occurs in the extremities, to prevent acting out of dreams or nightmares.Cardiac arrhythmias may selectively occur during REM sleep. REM sleep has a major effect on Consolidation of memory (i.e. Converting short term memory into long term memory); Daytime efficiency; Fine motor skills; and Creativity. Sleep-wake cycles are regulated an internal biological clock which is influenced by a balance of hormones and neurotransmitters.
Insomnia is clinically defined as difficulty with the initiation, maintenance, duration or quality of sleep causing impairment of daytime functioning, despite adequate opportunity for normal sleep. Insomnia affects every aspect of our functioning as will be pointed out in other articles on this website including chronic pain, depression, anxiety, ability to concentrate and memorize important information, weight management, cardiovascular health, creativity, athletic performance, growth during adolescence,, fibromyalgia, addiction and dependency to alcohol and drugs, immune system functioning, respiratory illness,, ability to adapt to traveling and schedule changes, and much more. Illness worsens insomnia and likewise, insomnia worsens illness. For example difficulty falling asleep correlates with an increased risk of dying from cardiovascular disease.