Man : Out (Sleep)

Man Sleep

         Sleep is defined as 

          a.  a person in the state of unconsciousness 

          b. from which the person can be aroused from this unconsciousness. 

       Coma is an unconscious state from which a person cannot be aroused. Sleep is essential for the normal, healthy functioning of the human body.

      Physiologically, sleep is a complex process of restoration and rejuvenating the body. Scientists still do not have a definitive explanation for why humans have a need for sleep. Sleep is not a passive process or "switching off" of body functions; sleep has many physiologic processes including the 

    i. processing of experiences and 

    ii. the consolidation of memories.

    Modern sleep scientists believe that sleep deprivation has deleterious effects on mental concentration, memory, mood, and quality of life. In addition, recent data indicate that sleep deprivation impairs endocrine and metabolic functions.

Physiology

      Sleep is now known to be a dynamic process and our brains are active during sleep. Sleep affects our physical and mental health and is essential for the normal functioning of all the systems of our body, including the immune system. The effect of sleep on the immune system affects one's ability to fight disease and endure sickness.

Stages of sleep

  In sleeping, there are two distinct states that alternate in cycles and reflect differing levels of neuronal activity. Each state is characterized by a different type of brain wave (electrical activity that is recorded with the help of electrodes placed on the skull) activity. Sleep consists of non-rapid eye movement (NREM) and rapid eye movement (REM) sleep.

       a.     rapid eye movement (REM) sleep, and

       b.   Non-rapid eye movement (NREM) sleep. 
           NREM is further subdivided into the following four stages.

       The stages of NREM sleep and REM sleep cycle over and over again during a night's sleep. Stages I, II, III, and IV are followed by REM sleep. A complete sleep cycle, from the beginning of stage I to the end of REM sleep, usually takes about one and a half hours.

A night's sleep is divided into three equal time periods: Sleep in the first third of the night, which comprises the highest percentage of NREM; sleep in the middle third of the night; and sleep in the last third of the night, the majority of which is REM. Awakening after a full night's sleep is usually from REM sleep.

     i.   REM sleep (rapid-eye movement):

     

a. REM sleep represents 20% to 25% of the total sleep time. 
b. REM sleep follows NREM sleep and occurs four to five times during a 8- to 9-hour sleep period. 
c. The first REM period of the night may be less than 10 minutes in duration, while the last may exceed 60 minutes. In a normal night’s sleep, bouts of REM occur every 90 minutes.

    When the person is extremely sleepy, the duration of each bout of REM sleep is very short or it may even be absent. REM sleep is usually associated with dreaming. 

    During REM sleep, 

     i. the eyeballs move rapidly, 

    ii. the heart rate and breathing become rapid and irregular, and the blood pressure rises. 

    iii. The muscles of the body are virtually paralyzed. 

   iv. The brain is highly active during REM sleep, and the overall brain metabolism may be increased by as much as 20%. The electrical activity recorded in the brain during REM sleep is similar to that which is recorded during wakefulness.

    Sleep typically occurs in cycles that range from 90 to 120 minutes in length, with 4-5 cycles occurring during each night's sleep. In the first half of the night, there is a transition from wakefulness into stage N1 sleep, then to stages N2, and N3. Stages N2 and N3 then reappear, followed by the first instance of REM sleep. Cycles of stage N2 and REM sleep alternate with each other for the second half of the night.

Disruptions in the entire sleep cycle or in the individual phases are believed to account for the various types of sleep disorders.

 ii.  NREM (non-rapid eye movement):

  NREM  sleep has traditionally been considered to be divided into 3 stages :\

  NREM stage 1: This is a stage between sleep and wakefulness. 
    a. The muscles are active, and    
    b. the eyes roll slowly, opening and closing moderately. 
This is the lightest stage of sleep, and people may not always perceive they are asleep when in this stage. 

NREM stage 2: In this stage, it gradually becomes harder to awaken the sleeper; in this stage the alpha waves of the previous stage are interrupted by abrupt activity called sleep spindles and k complex. It is a true sleep state, and accounts for 40% to 50% of sleep time.

NREM stage 3: formerly divided into stages 3 and 4, is called slow wave sleep - which is caused by the preoptic area that consists of delta activity, high amplitude waves at less than 3.5 Hz. The sleeper is less responsive to the environment; many environmental stimuli no longer produce any reactions. It has been called deep sleep, delta sleep, or slow wave sleep. This stage accounts for about 20% of sleep in young adults.

Cycle of Sleep

          Sleep typically occurs in cycles that range from 90 to 120 minutes in length, with 4-5 cycles occurring during each night's sleep. In the first half of the night, there is a transition from wakefulness into stage N1 sleep, then to stages N2, and N3. Stages N2 and N3 then reappear, followed by the first instance of REM sleep. Cycles of stage N2 and REM sleep alternate with each other for the second half of the night.

Disruptions in the entire sleep cycle or in the individual phases are believed to account for the various types of sleep disorder

Psychology
Circadian Rhythms That Influence Sleep

    Biological variations that occur in the body for 24 hours are called circadian rhythms. Every human are control by the body's biological clock called Circadian rhythms. The bodily functions of human follow the biologic clock, but the most important are the circadian rhythm of sleep and wakefulness. One of the several body rhythms modulated by the hypothalamus (a part of the brain).

   Light directly affects the circadian sleep rhythm. Light is called a "zeitgeber," a German word meaning time-giver, because it sets the biological clock. A practical purpose has been proposed for the circadian rhythm, using the analogy of the brain being somewhat like a battery charging during sleep and discharging during wakefulness.

  Human body temperature cycles are also control by the hypothalamus. An increase in body temperature is seen during the course of the day and a decrease is observed during the night. The temperature peaks and troughs mirror the sleep rhythm. People who are alert late in the evening (evening types) have body temperature peaks late in the evening, while those who find themselves most alert early in the morning (morning types) have body temperature peaks early in the evening.

   Melatotnin (a chemical produced by the pineal gland in the brain) is a modulator of light entrainment. It is secreted maximally during the night. Prolactin, testosterone, and growth hormone also demonstrate circadian rhythms, with maximal secretion during the night.

The beeping of the alarm clock or the timing of meals an external stimulus can affect to a certain degree the Circadian rhythms. When we cross time zones, our circadian rhythms get disrupted leading to jet lag. It usually takes several days for our body rhythms to adjust to the new time. So do to people who work during nights or work in shifts. These people's wake time conflicts with powerful sleep-regulating cues like sunlight, they often become uncontrollably drowsy during work or may have difficulty falling asleep during their off time. Their biological clock wants to do one thing while they are doing something entirely different. People working in shifts have an increased risk of heart, gastrointestinal, emotional, and mental problems. All these problems may be related to the disruption of the circadian sleep rhythm.

Importance of Sleep

   In humans, the metabolic activity of the brain decreases significantly after 24 hours of sustained wakefulness. Sleep deprivation results in a 
 a. decrease in body temperature, 
  b. a decrease in immune system function as measured by white blood cell count (the soldiers of the body), and 
  c. a decrease in the release of growth hormone. Sleep deprivation can also cause increased heart rate variability.

For our nervous systems to work properly, sleep is needed. Sleep deprivation makes a person drowsy and unable to concentrate the next day. It also leads to impairment of memory and physical performance and reduced ability to carry out mathematical calculations. If sleep deprivation continues, hallucinations and mood swings may develop.

Release of growth hormone in children and young adults takes place during deep sleep. Most cells of the body show increased production and reduced breakdown of proteins during deep sleep. Sleep helps humans maintain optimal emotional and social functioning while we are awake by giving rest during sleep to the parts of the brain that control emotions and social interactions.

Sleep at Different Stages of Life

a.      Infancy

     Infants have an overall greater total sleep time than any other age group. Their sleep time can be divided into multiple periods. In newborns, the total sleep duration in a day can be 14 to 16 hours. Over the first several months of life, sleep time decreases; by age 5 to 6 months, sleep consolidates into an overnight period with at least one nap during the day.

REM sleep in infants represents a larger percentage of the total sleep at the expense of stages III and IV. Until age 3 to 4 months, newborns transition from wakefulness into REM sleep. Thereafter, wakefulness begins to transition directly into NREM sleep.

b.      Adulthood

    In adults, sleep of 8 to 8.4 hours is considered fully restorative. In some cultures, total sleep is often divided into an overnight sleep period of 6 to 7 hours and a nap of 1 to 2 hours.

Some people may need as little as 5 hours or as much as 10 hours of sleep every day. The period of time a person sleeps depends also on the fact whether he or she has been deprived of sleep in previous days. Sleeping too little creates a "sleep debt." This debt needs to be adjusted by sleeping for longer periods over the next few days. People who sleep less have an impairment of judgment and reaction time.

c.       Old age

    People tend to sleep more lightly and for shorter periods as they get older. In elderly persons, the time spent in stages III and IV decreases by 10% to 15%, and the time in stage II increases by 5% compared to young adults, representing an overall decrease in total sleep duration.

Time taken to fall asleep and the number and duration of overnight arousal periods increase. Thus, to have a fully restorative sleep, the total time in bed must increase. If the elderly person does not increase the total time in bed, complaints of insomnia and chronic sleepiness may occur.

Sleep fragmentation results from the increase in overnight arousals and may be exacerbated by the increasing number of medical conditions related to old age, including sleep apnea (interrupted breathing during sleep), musculoskeletal disorders, and cardiopulmonary disease.

Substances That Alter Sleep

     Sleep and wakefulness are influenced by different neurotransmitters in the brain. Some substances can change the balance of these neurotransmitters and affect our sleep and wakefulness. Caffeinated drinks (for example, coffee ) and medicines (for example, diet pills) stimulate some parts of the brain and can cause difficulty in falling asleep. Many drugs prescribed for the treatment of  depression suppress REM sleep.

    People who smoke heavily often sleep very lightly and have reduced duration of REM sleep. Heavy smokers tend to wake up after 3 or 4 hours of sleep due to nicotine  withdrawal. Some people who have insomnia may use alcohol. Even though alcohol may help people to fall into light sleep, it deprives them of REM sleep and the deeper and more restorative stages of sleep. Instead, it keeps them in the lighter stages of sleep from which they can be awakened easily.

     During REM sleep, we lose some of our ability to regulate our body temperature. Therefore, abnormally hot or cold temperatures can disrupt our REM sleep. If our REM sleep is disturbed, the normal sleep cycle progression is affected during the next sleeping time and there is a possibility of slipping directly into REM sleep and going through long periods of REM sleep until the duration of REM sleep that is lost is caught up.

How much sleep does a person need?

    Individuals vary greatly in their need for sleep; there are no established criteria to determine exactly how much sleep a person needs. Eight hours or more may be necessary for some people, while others may consider this to be too much sleep.

The National Institutes of Health (NIH) suggests that:

      a.  average adults need about 7 to 9 hours of sleep each night.  
     b. Newborn babies, by contrast, sleep from 16 to 18 hours a day.  
     c. Preschool aged children typically sleep between 10 and 12 hours a day. 
     d. Older, school-aged children  and teens  need at least 9 hours of sleep a night. 

   e. Women in the first trimester of pregnancy need a few more hours' sleep than is usual for them.

Does the amount of sleep we need change as we age?

     Changes in the sleep cycle do occur with aging. Deep or slow wave sleep (Stage N3) sleep declines as we age, while light sleep (Stage N1) increases with age, so that older adults may spend less time in the more restorative stages of sleep and more time in lighter sleep. Older people are also more easily aroused from sleep. While some people believe that older adults need less sleep as they get older, there is no scientific evidence that older people need less sleep than younger adults.

What are signs and symptoms of sleep deprivation?

   Feeling tired or drowsy at any time during the day is a symptom of not having enough sleep. Being able to fall asleep within 5 minutes of lying down in the evening also may be a sign a person may be suffering from sleep deprivation. People who suffer from sleep deprivation often experience so-called "microsleeps," which are short bursts of sleep in an otherwise awake person.

Sleep-deprived people perform poorly on tests such as driving simulators and tests of hand-eye coordination. Sleep deprivation can also magnify the effects of alcohol, meaning that a sleep-deprived person will be more susceptible to becoming impaired after alcohol consumption than a well-rested person.  Caffeine and other stimulants cannot successfully overcome the drowsiness associated with sleep deprivation.

We should all be merciless about defending our sleep. 

We think we can sacrifice it temporarily; 

we won't likely suffer any adverse effects. 

The problem comes in when we do so repeatedly, 

thinking perhaps because initially we don't suffer any negative consequences 

that we can continue to function normally in the long term. 

It is far from the truth. 

We need the rest and rested well 

to feel more capable of handling the obstacles that arise in life. 

We should make every effort to conceive our sleep 

as a top priority rather than 

something we just happen to do at the end of the day.

Excerpt and extract taken with thanks from:

Wikipedia
http://www.medicinenet.com/sleep

Author: Michael B. Russo, MD