On the list of American’s most frequent health complaints, difficulty sleeping is second only to the common cold. It is estimated that there are 60 million people in United States who perceive themselves as having trouble sleeping. A simple behavioral definition of sleep, used by Carskadon and Dement in 1994, is a reversible behavioral condition of perceptual detachment from and unresponsiveness to the surroundings and environment. Sleep has also been described as a condition of concentrated reaction to external stimuli, a changed state of perception from which an individual can be aroused if the stimulus is of sufficient degree and magnitude. The sleeping person does not sense their surroundings nor respond to them anywhere near the degree they do when awake. Although the sleeping person does not sense his surroundings, there is not a total lack of sensing and perceiving external stimuli. Intense, discomforting, or especially meaningful stimuli can cause a sudden awakening. Sleep is an extremely complex combination of both physiological and behavioral processes. It was not until the middle of the twentieth century that scientists devised objective ways of determining if a person was in a state of sleep using technological advances enabling brain waves and other bodily functions to be recorded (Kryger, 2004). They also discovered that sleep is of several types called stages.
It was not long before these methods, called polysomnography, became refined and universally accepted such that today the determination of states of sleep and wakefulness is reliable and valid. Polysomnography involves the recording of three things – brain waves, eye movements, and neck muscle tension. Sleep stages exist and can be measured using an electroencephalogram (EEG) which measures the brain waves and other instruments such as the electro-oculogram or EOG that determines the eye movements and EMG or electromyogram that measures the tension in the neck muscle. Within the process of sleep, two states exist that have distinct manifestations: the rapid eye movement or the REM and the non rapid eye movement or NREM. NREM consists of four phases or stages, along with the rapid eye movement (REM) with one stage, so together; they have five significant period of sleep that cycle all through the night.
The hazy phase or the stage one of the NREM phase is the period of time in sleeping that you are just sounding asleep. It is a extremely gentle sleep, and can be easily interrupted – if somebody open or turned on a light or creates a noise, one will most likely to be awaken. Frequently, if an individual is awakened from the initial phase of sleeping, he or she won’t even identify he was asleep. The predominant rhythm or the alpha rhythm is a 8 to 12 round per second and is seen with eyes closed for the period of comfortable wakefulness, is trimmed down to fewer than 50 percent of the entire brain-wave movement, eyes moves slowly rolling back and forth, muscle tone turned out to be more relaxed, and might experience unexpected muscle movements or hypnic jerks that nudge someone to be awaken, at times with the feeling that one is falling. Stage two in general is believed to be the “baseline” of sleep – the distinct preliminary stage. In this stage, an individual is still in a moderately light sleep, and fairly easy to arouse, but the heart pace slows down and the temperature falls in preparation for the deeper sleep to occur. The brain movement, which can be determined by scalp electrodes in a sleep lab, will show slower waves mixed with sporadic bursts of faster waves called sleep spindles and also a brain wave pattern known as K-complexes that look like the letter “K”. Sleep spindles and K-complexes are hallmarks of stage 2 sleep. As an adult, an individual will consume approximately half of their entire sleeping time in stage 2. Stage three is the shifting of the delta sleep or slow-wave sleep. In the middle of this stage a high-voltage for about twenty to fifty percent, slow-wave movement known as delta waves, moves at one to three cycles per every second (Billiard & Kent, 2003). Stages 3 and 4 are frequently classified mutually because there is not much a great deal with the purpose of distinguishing them from a physiological point of view. It is a common misunderstanding that the deepest sleep is the REM sleep. But in fact, the deepest sleep is the NREM stage four that is directly go after the stage three. When an individual have been deprived in sleeping, his body requires a delta sleep and will strive to make up for the used time by going to the NREM stage four quicker and keeping him there longer. While people state that somebody is in a “dead sleep” or “out like light” the individual are in almost certainly in the phase of NREM stage three or four, once it is very hard to stir him up. This period of sleeping is where the sleepwalking and sleep terrors are mainly possible to take place. Stage four is in addition, the phase in which it is considerate that the body perform most of its restoration. Once an individual is in the stage of REM, the person will frequently demonstrate bursts of back-and forth movements of the eye and eye wavers, probably in concurrence with dreams. This phase is the time when the most clear and prolonged dreaming take place. The brain is extremely dynamic as can be observed on sleep graphs, it appears approximately similar in the brain activity of a conscious individual, but the body is momentarily paralyzed by an active, general inhibition coming from the lower part of the brain. The muscles are “shut down” and totally still, and it is assumed that this is to protect us from acting out our dreams. The blood flow to the brain increases; heart rate escalates and blood pressure rises; respiration becomes faster, erratic and shallower, with proliferation in oxygen utilization; metabolism increases and sexual arousal happens (Kandel, Schwartz, & Jessell, 2000). REM sleep has the notion of specifically important in memory and learning processing. The ease of arousing someone from REM sleep varies, but it’s usually far easier to wake someone from REM sleep than from stage 3 or 4 sleep. You can also become alert much more quickly when something wakes you out of REM sleep than when you are aroused out of delta NREM sleep. About 20 to 25 percent of an adult’s total sleep time is spent in the REM stage.
Sleep cycle does not progress as stages 1, 2, 3, and 4, the REM, the repeat but it often doesn’t occur in quite such a regular manner. Instead, a typical adult sleep cycle is like for stage one is for up to 10 minutes, 10 to 15 minutes for stage two, for about 5 minutes for stage three, 20 to 40 minutes for stage four, then back to stage three for a minute or two, stage two for 5 to 10 minutes, then for up to 5 minutes for the REM stage (Chokroverty, 2001). The first REM stage begins about 90 minutes into sleep, and then the cycle starts again about 90 minutes throughout the night. During the earlier cycles, stages 3 and 4 are at their longest, but they get shorter and may drop out altogether in later cycles, with stage 2 lengthening to fill in the gap. The REM stage gets longer in the later cycles. In total, you’ll spend abut 75 to 80 percent of the night in NREM sleep and 20 to 25 percent in REM sleep.
Many functions of sleep have been proposed, and it is described as a restorative, protective, instinctive or ethnologically adaptive process according to Hodgson in 1991, contributing to physiological and psychological restoration. Traditionally, sleeping is viewed as a time of restoration and preparation for the next period of wakefulness. Sleep is of most important to the functioning of the cerebral cortex; this is the most clearly shown by the need for recovery sleep following sleep loss or deprivation. Although most other parts of the body can relax and recover during wakefulness, the cerebrum cannot do so. Even though the eyes are closed and the mind may be blank, the waking brain remains highly active. (Billiard and Kent, 2003). Moreover Feinberg (1989) found a high waking metabolic rate in 3 to 8 year olds, which may suggest the need for greater recovery sleep in children; indeed, children in this age range show substantially greater amounts of stage 3 and stage 4 sleeps in the first third of the night than young adults. During NREM sleep, biological functions slow. A healthy adult’s normal rate throughout the day averages 70 to 80 beats per minute or less if the individual is in excellent physical condition. However, during sleep the heart rate falls to 60 beats per minute or less. Clearly, then, restful sleep is beneficial in preserving cardiac functions. Sleep is needed to routinely restore biological processes. During NREM stage 4 the body releases growth hormone for the repair and renewal of epithelial and specialized cells such as a brain cells (Moorcroft & Belcher, 2003). Other studies have shown that cell division and protein synthesis for the regeneration of tissues such as the bone marrow, gastric mucosa, skin, or brain takes place while resting and sleeping (Martin, 2005). Non-rapid eye movement sleep may be especially important in children, who experienced more stage 4 sleep. The body conserves energy during sleep. The skeletal muscles relax progressively, and the absence of muscular contraction preserves chemical energy for cellular processes. Lowering of the basal metabolic rate further conserves the body’s energy supply. REM sleep appears to be important for psychological restoration. REM sleep is associated with changes in cerebral blood flow, increases cortical activity, increased oxygen consumption, and adrenaline release. This association may assist with memory storage, learning, and emotional adaptation (Kandel, Schwartz, & Jessell, 2000).
Sleep dilemmas affect practically every part of the day-to-day living of a person, such as the mood, work performance, energy level, and mental alertness. A 2005 survey by the NSF or National Sleep Foundation found out that, during the preceding year, 75 percent of adults obtain at least one sign of a sleep trouble, such as snoring or waking plenty of hours during the night, and 54 percent encountered an indication of insomnia. We pay a high price for getting an insufficient amount of sleep individually and as a society. To be deficient in sleep is directly associated to poor health, and researches suggests that it increases the risk of heart disease, obesity and diabetes. According to the 2005 NSF survey, almost three in ten working adults stated that they have missed or made errors at work because of sleep deprivation. Nearly one-fourth of adults say they have sex less frequently or have lost interest in sex for the reason that they are too sleepy. Sleep deprivation causes fatigue; sleepiness; weakening of performance, and diminishment of mental concentration and intellectual ability. It also heightens up the chances of accidents at work and especially during driving. Thus sleep deprivation worsen the value of life and endanger both individual and public safety.
Martin, P. (2005). Counting Sheep: The Science and Pleasures of Sleep and Dreams. New York, NY: St. Martin’s Press
Kryger, M. (2004). A Woman’s Guide to Sleep Disorders. New York, NY: McGraw-Hill Professional
Moorcroft, W. and Belcher, P. (2003). Understanding Sleep and Dreaming. New York, NY: Kluwer Academic/ Plenum Publishers
Billiard, M. and Kent, A. (2003). Sleep: Physiology, Investigations, and Medicine. New York, NY: Kluwer Academic/ Plenum Publishers
Chokroverty, S. (2001). 100 Questions about Sleep and Sleep Disorders: Sleep Disorders. Massachusetts, USA: Blackwell Publishing
Kandel, E., Schwartz, J., and Jessell, T. (2000). Principles of Neural Science. New York, NY: McGraw-Hill Professional