SLEEP

Sleep

A condition of body and mind such as that which typically recurs for several hours every night, in which the nervous system is inactive,...

What is Sleep?

We all have at least a vague notion of what sleep is, but that doesn't mean that defining this mysterious part of our lives is simple. After all, detailed analysis of our own sleep isn't really an option, given that we rarely know that we're sleeping when we're asleep. And even if we observe the sleep of others, so much of what they experience—changes in the functions of their brains and bodies—is not easily seen from the outside.

Sleep scientists have explored these changes in depth, and their definition of sleep is tied to characteristic patterns of brain waves and other physiological functions. Features in this section describe and explain the significance of typical sleep patterns, as well as a variety of factors that disrupt these patterns.

Every night, nearly every person undergoes a remarkable change: we leave waking consciousness and for hours traverse a landscape of dreams and deep sleep. When we wake, we typically remember little or nothing about the hours that have just passed. Except in rare instances, we never contemplate and appreciate that we are sleeping while we are asleep. Thus, although everyone sleeps, most people would be hard-pressed to precisely define sleep. All organisms exhibit daily patterns of rest and activity that resemble the daily sleep and wakefulness patterns seen in humans. From observing changes in behavior and responsiveness, scientists have noted the following characteristics that accompany and in many ways define sleep:

    Sleep is a period of reduced activity.

    Sleep is associated with a typical posture, such as lying down with eyes closed in humans.

    Sleep results in a decreased responsiveness to external stimuli.

    Sleep is a state that is relatively easy to reverse (this distinguishes sleep from other states of reduced consciousness, such as hibernation and coma).

From observations of behavioral changes that accompany sleep and simultaneous physiological changes, scientists now define sleep in humans based on brain wave activity patterns and other physiological changes as described below.

Physiological Changes During Sleep

Many physiological variables are controlled during wakefulness at levels that are optimal for the body’s functioning. Our temperature, blood pressure, and levels of oxygen, carbon dioxide, and glucose in the blood remain quite constant during wakefulness. During sleep, however, physiological demands are reduced and temperature and blood pressure drop. In general, many of our physiological functions such as brain wave activity, breathing, and heart rate are quite variable when we are awake or during REM sleep, but are extremely regular when we are in non-REM sleep.

Brain Activity in Sleep

For centuries, physicians believed that sleep was a period of brain inactivity, yet research over the last 60 
years has shown us that the brain remains active during sleep. There is a progressive decrease in the activation or "firing" rate of most neurons throughout the brain as sleep progresses from wakefulness to non-REM sleep. Also, the patterns of neuron firing change from a seemingly random and variable activity pattern during wakefulness, to a much more coordinated and synchronous pattern during non-REM sleep.

During REM sleep (the stage of sleep most associated with dreaming) there is an increase in the firing rate of most neurons throughout the brain, as compared to non-REM sleep. In fact, the brain in REM sleep can even be more active than when we are awake. Patterns of brain activity during REM sleep are more random and variable, similar to during wakefulness. This pattern of brain activity during REM sleep probably underlies the intense dreaming that occurs during this state.

How Much Sleep Do You Need?

When you’re scrambling to meet the countless demands of your day, cutting back on sleep might seem like the only answer. Who can afford to spend so much time sleeping, anyway? The truth is you can’t afford not to. Even minimal sleep loss takes a toll on your mood, energy, and ability to handle stress. Learn how to determine your nightly sleep needs and what you can do to bounce back from chronic sleep loss and get on a healthy sleep schedule.

Sleep isn’t exactly a time when your body and brain shut off. While you rest, your brain stays busy, overseeing a wide variety of biological maintenance that keeps your body running in top condition, preparing you for the day ahead. Without enough hours of restorative sleep, you won’t be able to work, learn, create, and communicate at a level even close to your true potential. Regularly skimp on “service” and you’re headed for a major mental and physical breakdown. 

How many hours of sleep do you need?

According to the National Institutes of Health, the average adult sleeps less than seven hours per night. In today’s fast-paced society, six or seven hours of sleep may sound pretty good. In reality, though, it’s a recipe for chronic sleep deprivation.

There is a big difference between the amount of sleep you can get by on and the amount you need to function optimally. Just because you're able to operate on seven hours of sleep doesn't mean you wouldn't feel a lot better and get more done if you spent an extra hour or two in bed.

While sleep requirements vary slightly from person to person, most healthy adults need between seven and a half to nine hours of sleep per night to function at their best. Children and teens need even more (see box at right). And despite the notion that our sleep needs decrease with age, older people still need at least seven and a half to eight hours of sleep. Since older adults often have trouble sleeping this long at night, daytime naps can help fill in the gap.

The best way to figure out if you're meeting your sleep needs is to evaluate how you feel as you go about your day. If you're logging enough hours, you'll feel energetic and alert all day long, from the moment you wake up until your regular bedtime.

Sleep Problems/Sleep Disorder

Most of us have experienced trouble sleeping at one time or another. This is normal and usually temporary, due to stress or other outside factors. But if sleep problems are a regular occurrence and interfere with your daily life, you may be suffering from a sleep disorder. Sleep disorders cause more than just sleepiness. The lack of quality sleep can have a negative impact on your energy, emotional balance, and health. If you’re experiencing sleeping problems, learn about the symptoms of common sleep disorders, what you can do to help yourself, and when to see a doctor.

Slee Pattern

Insomnia: (Sleep)

Insomnia is the inability to get the amount of sleep you need to wake up feeling rested and refreshed, is the most common sleep complaint. Insomnia is often a symptom of another problem, such as stress, anxiety, depression, or an underlying health condition. It can also be caused by lifestyle choices, including the medications you take, lack of exercise, jet lag, or even the amount of coffee you drink.

•     Difficulty falling asleep at night or getting back to sleep after waking during the night
•     Waking up frequently during the night
•     Your sleep feels light, fragmented, or exhausting
•     You need to take something (sleeping pills, nightcap, supplements) in order to get to sleep
•     Sleepiness and low energy during the day

Whatever the cause of your insomnia, being mindful of your sleep habits and learning to relax will help you sleep better and feel better. The good news is that most cases of insomnia can be cured with lifestyle changes you can make on your own—without relying on sleep specialists or turning to prescription or over-the-counter sleeping pills. 

Sleep Apnea

Sleep apnea occurs when your breathing is disrupted during sleep. Men, overweight people, and people over 40 are at greater risk for sleep apnea. Untreated sleep apnea can cause hypertension, stroke, or heart failure.

Sleep Cycle/ Stages

During the earliest phases of sleep, you are still relatively awake and alert. The brain produces what are known as beta waves, which are small and fast. As the brain begins to relax and slow down, slower waves known as alpha waves are produced. During this time when you are not quite asleep, you may experience strange and extremely vivid sensations known as hypnagogic hallucinations. Common examples of this phenomenon include feeling like you are falling or hearing someone call your name.

Another very common event during this period is known as a myoclonic jerk. If you've ever startled suddenly for seemingly no reason at all, then you have experienced this odd phenomenon. While it may seem unusual, these myoclonic jerks are actually quite common.

Sleep Stage 1:

Stage 1 is the beginning of the sleep cycle, and is a relatively light stage of sleep. Stage 1 can be considered a transition period between wakefulness and sleep. In Stage 1, the brain produces high amplitude theta waves, which are very slow brain waves. This period of sleep lasts only a brief time (around 5-10 minutes). If you awaken someone during this stage, they might report that they weren't really asleep.

Sleep Stage 2:

Stage 2 is the second stage of sleep and lasts for approximately 20 minutes. The brain begins to produce bursts of rapid, rhythmic brain wave activity known as sleep spindles. Body temperature starts to decrease and heart rate begins to slow.

Sleep Stage 3:

Deep, slow brain waves known as delta waves begin to emerge during stage 3 sleep. Stage 3 is a transitional period between light sleep and a very deep sleep.

Sleep Stage 4:

Stage 4 is sometimes referred to as delta sleep because of the slow brain waves known as delta waves that occur during this time. Stage 4 is a deep sleep that lasts for approximately 30 minutes. Bed-wetting and sleepwalking are most likely to occur at the end of stage 4 sleep.

Sleep Stage 5:

Most dreaming occurs during the fifth stage of sleep, known as rapid eye movement (REM) sleep. REM sleep is characterized by eye movement, increased respiration rate and increased brain activity. REM sleep is also referred to as paradoxical sleep because while the brain and other body systems become more active, muscles become more relaxed. Dreaming occurs due because of increased brain activity, but voluntary muscles become paralyzed.