Sleep

Sleep is a naturally recurring state characterized by reduced or absent consciousness, relatively suspended sensory activity, and inactivity of nearly all voluntary muscles. It is distinguished from quiet wakefulness by a decreased ability to react to stimuli, and is more easily reversible than being in hibernation or a coma. Sleep is a heightened anabolic state, accentuating the growth and rejuvenation of the immune, nervous, skeletal and muscular systems. It is observed in all mammals, all birds, and many reptiles, amphibians, and fish.

The purposes and mechanisms of sleep are only partially clear and are the subject of intense research. Sleep is often thought to help conserve energy, but decreases metabolism only about 5–10%. Hibernating animals need to sleep despite the hypometabolism seen in hibernation, and must return from hypothermia to euthermia in order to sleep, making sleeping "energetically expensive."

Read more about Sleep:  Siesta or Nap, Sleep Debt, Genetics, Functions, Dreaming, Insomnia, Obstructive Sleep Apnea, Other Sleep Disorders, Anthropology of Sleep, Sleep in Non-humans

Famous quotes containing the word sleep:

    I am Anne Rutledge who sleep beneath these weeds,
    Beloved in life of Abraham Lincoln,
    Wedded to him, not through union,
    But through separation
    Edgar Lee Masters (1869–1950)

    England! awake! awake! awake!
    Jerusalem thy sister calls!
    Why wilt thou sleep the sleep of death,
    And close her from thy ancient walls?
    William Blake (1757–1827)

    But a dog teaches a boy fidelity, perseverance, and to turn around three times before lying down—very important traits in times like these. In fact, just as soon as a dog comes along who, in addition to these qualities, also knows when to buy and sell stocks, he can be moved right up to the boy’s bedroom and the boy can sleep in the dog house.
    Robert Benchley (1889–1945)