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:
“Thou hast conquered, O pale Galilean; the world has grown grey from thy breath;
We have drunken of things Lethean; and fed on the fullness of death.
Laurel is green for a season, and love is sweet for a day;
But love grows bitter with treason, and laurel outlives not May.
Sleep, shall we sleep after all? for the world is not sweet in the
end;
For the old faiths loosen and fall, the new years ruin and rend.”
—A.C. (Algernon Charles)
“I pray that Allah may be moved
To drop sleep on her eyes because she loved.”
—Unknown. The Thousand and One Nights.
AWP. Anthology of World Poetry, An. Mark Van Doren, ed. (Rev. and enl. Ed., 1936)
“The age of puberty is a crisis in the age of man worth studying. It is the passage from the unconscious to the conscious; from the sleep of passions to their rage.”
—Ralph Waldo Emerson (1803–1882)