What is Sleep

Do you ever feel sleepy or are you “zone out” during the day?  Do you find it hard to wake up on Monday mornings?  If so, you are familiar with the powerful need for sleep.  However, you may not realize that sleep is as essential for our well-being as food and water.

It is estimated that 70 million Americans chronically suffer from a disorder of sleep and wakefulness, hindering daily functioning and adversely affecting health and longevity.

What is sleep?

Until the 1950s, most people thought of sleep as a passive, dormant part of our daily lives.  We now know that our brains are very active during sleep.  Moreover, sleep affects our daily functioning and our physical and mental health in many ways that we are just beginning to understand.

During sleep, we usually pass through four phases of sleep: stages 1, 2, 3, and REM (rapid eye movement) sleep.  These stages progress in a cycle from stage 1 to REM sleep, then the cycle starts over again with stage 1.  We spend almost 50 percent of our total sleep time in stage 2 sleep, about 20 percent in REM sleep, and the remaining 30 percent in the other stages.  Infants, by contrast, spend about half of their sleep time in REM sleep.

Read more about the stages of sleep

Stage 1

During stage 1, which is light sleep, we drift in and out of sleep and can be awakened easily.  Our eyes move very slowly and muscle activity slows.  People awakened from stage 1 sleep often remember fragmented visual images.  Many also experience sudden muscle contractions called hypnic myoclonia, often preceded by a sensation of starting to fall.  These sudden movements are similar to the “jump” we make when startled.

Stage 2

When we enter stage 2 sleep, our eye movements stop and our brain waves (fluctuations of electrical activity that can be measured by electrodes) become slower, with occasional bursts of rapid waves called sleep spindles.

Stage 3

Formerly divided into stages 3 and 4, Stage 3 is called slow wave sleep or deep sleep.  It is characterized by extremely slow brain waves called delta waves.  There is no eye movement or muscle activity.  People awakened during deep sleep do not adjust immediately and often feel groggy and disoriented for several minutes after they wake up.  Some children experience bed-wetting, night terrors, or sleepwalking during deep sleep.


REM, stands for Rapid Eye Movements, which are inherent to this stage of sleep.  When we switch into REM sleep, our breathing becomes more rapid, irregular, and shallow, our eyes jerk rapidly in various directions, and our limb muscles become temporarily paralyzed.  Our heart rate increases, our blood pressure rises, and males develop penile erections.  When people awaken during REM sleep, they often describe bizarre and illogical dreams.

The first REM sleep period usually occurs about 70 to 90 minutes after we fall asleep.  A complete sleep cycle takes 90 to 110 minutes on average.  The first sleep cycles each night contain relatively short REM periods and long periods of deep sleep.  As the night progresses, REM sleep periods increase in length while deep sleep decreases.  By morning, people spend nearly all their sleep time in stages 1, 2, and REM.

If our REM sleep is disrupted one night, our bodies don’t follow the normal sleep cycle progression the next time we doze off.  Instead, we often slip directly into REM sleep and go through extended periods of REM until we “catch up” on this stage of sleep.

What affects sleep?

Since sleep and wakefulness are influenced by different neurotransmitter signals in the brain, anything in our environment that changes the balance of these signals affects whether we feel alert or drowsy and how well we sleep.  You can find some common environmental factors that can affect sleep in the list below.

Some common environmental factors that can affect sleep

  • Emotional and cognative status; anxiety, depression and oveall brain funtion
  • Our exposure to light including sunlight man-made light as well as light sources found withing the sleeping environment
  • Medication and drug use including over-the-counter products and alcohol;
  • Nutritional Status; the type, quality and timing of our food intake and how our bodies assimilate it.
  • Temperature: the ability for us to regulate our body temperature and/or the ambient temperature of our sleep environment.
  • Exercise; though research shows that exercise is certainly good for one’s body and health, properly timing exercise is necessary to maximize the beneficial effects.  For example, a good workout can make you more alert, speed up your metabolism and energize you for the day ahead, but exercise right before bedtime can lead to a poor night’s sleep.  Sleep experts recommend exercising at least three hours before bedtime.

How much sleep do we need?

The amount of sleep each person needs depends on many factors, including age.  Infants generally require more and this need steadily decreases with age until adulthood.

Sleep Need by Age Chart

This chart represents the sleep needs by age according to the National Sleep Foundation.

Newborns (0–2 months) 12 to 18 hours
Infants (3–11 months) 14 to 15 hours
Toddlers (1–3 years) 12 to 14 hours
Preschoolers (3–5 years) 11 to 13 hours
School-age children (5–10 years) 10 to 11 hours
Adolescents (10–17 years) 8.5 to 9.25 hours
Adults, including elderly 7 to 9 hours

When to sleep

The optimal amount of sleep is not a meaningful concept unless the timing of that sleep is seen in relation to an individual’s circadian rhythms.   Circadian rhythms are regular changes in mental and physical characteristics that occur in the course of a day (circadian is Latin for “around a day”).  Most circadian rhythms are controlled by the body’s biological “clock.”  This clock, called the suprachiasmatic nucleus or SCN, is actually a pair of pinhead-sized brain structures that together contain about 20,000 neurons.

Signals from the SCN travel to several brain regions, including the pineal gland, which responds to light-induced signals by switching off production of the hormone melatonin.  The body’s level of melatonin normally increases after darkness falls, making people feel drowsy.  The SCN also governs functions that are synchronized with the sleep/wake cycle, including body temperature, hormone secretion, urine production, and changes in blood pressure.  Our biological cycles normally follow the 24-hour cycle of the sun, unless we are light deprived.

What does sleep do for us?

Although scientists are still trying to learn exactly why people need sleep, animal studies show that sleep is necessary for survival.  For example, while rats normally live for two to three years, those deprived of REM sleep survive only about 5 weeks on average, and rats deprived of all sleep stages live only about 3 weeks.

Read more

Sleep appears necessary for our nervous systems to work properly.  Too little sleep leaves us drowsy and unable to concentrate the next day.  It also leads to impaired memory and physical performance and reduced ability to carry out math calculations.  If sleep deprivation continues, hallucinations and mood swings may develop.  Some experts believe sleep gives neurons used while we are awake a chance to shut down and repair themselves.  Without sleep, neurons may become so depleted in energy or so polluted with byproducts of normal cellular activities that they begin to malfunction.  Sleep also may give the brain a chance to exercise important neuronal connections that might otherwise deteriorate from lack of activity.

Deep sleep coincides with the release of growth hormone in children and young adults.  Many of the body’s cells also show increased production and reduced breakdown of proteins during deep sleep.  Since proteins are the building blocks needed for cell growth and for repair of damage from factors like stress and ultraviolet rays, deep sleep may truly be “beauty sleep.”  Activity in parts of the brain that control emotions, decision-making processes, and social interactions is drastically reduced during deep sleep, suggesting that this type of sleep may help people maintain optimal emotional and social functioning while they are awake.  A study in rats also showed that certain nerve-signaling patterns which the rats generated during the day were repeated during deep sleep.  This pattern repetition may help encode memories and improve learning.

REM sleep stimulates the brain regions used in learning.  One study found that People taught a skill and then deprived of non-REM sleep could recall what they had learned after sleeping, while people deprived of REM sleep could not.

Some scientists believe dreams are the cortex’s attempt to find meaning in the random signals that it receives during REM sleep.  The cortex is the part of the brain that interprets and organizes information from the environment during consciousness.

Sleep deprivation and its effects

Experts say that if you feel drowsy during the day, even during boring activities, you haven’t had enough sleep.  If you routinely fall asleep within 5 minutes of lying down, you probably have severe sleep deprivation, possibly even a sleep disorder.  Microsleeps, or very brief episodes of sleep in an otherwise awake person, are another mark of sleep deprivation.  In many cases, people are not aware that they are experiencing microsleeps.

The cumulative long-term effects of sleep loss and sleep disorders have been associated with a wide range of deleterious health consequences.  Studies suggest that sleep loss may have pervasive effects on the cardiovascular, endocrine, immune, and nervous systems, other effects include the following:

• Anxiety symptoms • Depressed mood
• Decreased attention and working memory • Impaired physical and cognitive abilities
• Impaired learning • Emotional reactivity
• Obesity in adults and children • Gastrointestinal disorders
• Diabetes and impaired glucose tolerance • Cardiovascular disease and hypertension
• Impaired healing • Alcohol use

The widespread practice of “burning the candle at both ends”  has created so much sleep deprivation that what is really abnormal sleepiness is now thought of as the norm.  So if you’re suffering from sleepiness give us a call at 516.208.9360 to set up your free consultation and find out what can be done to help.


Institute of Medicine (US) Committee on Sleep Medicine and Research; Colten HR, Altevogt BM, editors.  Sleep Disorders and Sleep Deprivation: An Unmet Public Health Problem.  Washington (DC): National Academies Press (US); 2006.  3, Extent and Health Consequences of Chronic Sleep Loss and Sleep Disorders.  Available from: http://www.ncbi.nlm.nih.gov/books/NBK19961/