Sleep Centers of Middle Tennessee

Sleep Disorders 101

Posted on 14 Apr 2011 - 3:10 PM by navertise

The Assessment, Diagnosis & Treatment of Sleep: What is sleep? What types of sleep are there? When do we sleep? Why do we sleep? How much sleep do we need? What kind of sleep disorders are there?

What is Sleep?

Sleep is a mental and physical state of rest, during which time the person is usually inactive. There is a relative lack of awareness of environment and, to a certain degree, the person is unaware of stimuli. Sleep is usually accompanied by a decrease in body temperature, blood pressure, respiration rate, and most bodily functions. However, one’s brain remains active during sleep. In fact, tasks such as storing of short-term memory material into long-term memory and replenishment of neurochemicals occur during sleep.

Structure of Normal Sleep

There are two distinct types of sleep: 1) Rapid Eye Movement (REM) sleep (also known as dreaming sleep), and 2) Non-REM (NREM) sleep. Sleep is composed of 5 stages. Stages I-IV are known as NREM sleep (with stages III & IV being deep sleep). Stage V is REM sleep. Humans generally alternate between REM and NREM in 90-110 minute cycles. The process is as follows: once asleep, we move into stage I, then cycle through stages II – IV in roughly 30-40 minutes; we cycle back briefly through stage III and II, then REM. This process normally occurs 4-5 times per night.

When Do We Sleep?

Humans respond to circadian rhythms, or a “biological clock.” Certain structures in the brain (the superchiasmatic nucleus) are responsible for coordinating the biological clock. These brain structures are sensitive to light and dark. Some have argued that this results in daytime sleep being less restful than night sleep. Daylight normally triggers periods of wakefulness. As humans, we experience “sleepy peaks” which occur every 12 hours – at night and in the afternoon.

Why Do We Sleep?

The two main reasons for sleeping are:

  1. Restoration – rejuvenates, refreshes; allows brain to perform certain tasks (e.g., memory), allows certain physiological processes to take place (e.g., replenishment of biochemicals)
  2. Functioning – amount and quality of sleep directly impacts how functional a person is during the day

Sleep is a necessary biological function, and deprivation can have many negative effects, such as: irritability, decreased short-term memory, decreased attention/concentration, mood swings, decrease in immune system function, and ultimately…death. It is estimated that approximately 50% of Americans are sleep deprived. This often results in accidents, and has resulted in the development of legislation against sleepy driving in some states.

How much sleep does one need?

It is generally agreed that the average adult needs 6-8 hours. Some have argued that certain people need only a few hours of sleep per night, while other people may need as many as ten hours of sleep per night. If one is sleep deprived, a cumulative effect has been noted to occur over time, known as a “sleep debt.” This sleep debt must eventually be “repaid” in full, at which time a person feels rested.

Sleep Disorders

Sleep is important, and has been given far too little attention in the past. It has just been in the past few decades that scientists and researchers have come to appreciate the importance of sleep for maintaining good health. Decreased quality or quantity of sleep can be dangerous on multiple levels, as can being too sleepy (these two are often related). If you are not getting enough sleep despite reasonable efforts related to scheduling, or are sleeping too much, you may have a sleep disorder.

Sleep Disorders are categorized into two broad groups: Dyssomnias and Parasomnias. It is estimated that 40 million American suffer from chronic, long-term sleep disorders, and another 20 to 30 million deal with sleep disorders on a more irregular basis.