Sleep: Understanding the Basics

1. Causes of Fatigue Slideshow Pictures
2. Sleep Quiz: Test Your Medical IQ
3. Foods That Help or Harm Your Sleep Slideshow

• Facts on Sleep
• Importance of Sleep
• Stages of Sleep
• Sleep at Different Stages of Life
• Circadian Rhythms That Influence Sleep
• Substances That Alter Sleep
• Sleep Deprivation
• How to Fall Asleep Fast

• Sleep is defined as a state of unconsciousness from which a person can be aroused, therefore, external stimuli have no effect. In this state, the brain is relatively more responsive to internal stimuli than external stimuli.
• Sleep should be distinguished from coma. Coma is an unconscious state from which a person cannot be aroused.
• Sleep is essential for the normal, healthy functioning of the human body. It is a complicated physiological phenomenon that scientists do not fully understand.
• Historically, sleep was thought to be a passive state. However, 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.
• Brain activity during sleep and wakefulness is a result of different activating and inhibiting forces that are generated within the brain. Neurotransmitters (chemicals involved in nerve signaling) control whether one is asleep or awake by acting on nerve cells (neurons) in different parts of the brain.
• Neurons located in the brainstem cause sleep by inhibiting other parts of the brain that keep a person awake.

Animal studies have shown that sleep is necessary for survival. The normal life span of rats is 2 to 3 years. However, rats deprived of sleep live for only about 3 weeks. They also develop abnormally low body temperatures and sores on their tails and paws. The sores probably develop because of impairment of the rats' immune systems.

In humans, it has been demonstrated that the metabolic activity of the brain decreases significantly after 24 hours of sustained wakefulness. Sleep deprivation results in a decrease in body temperature, a decrease in immune system function as measured by white blood cell count (the soldiers of the body), and 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.

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