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:
“Bid a strong ghost stand at the head
That my Michael may sleep sound,
Nor cry, not turn in the bed
Till his morning meal come round;
And may departing twilight keep
All dread afar till morning’s back....”
—William Butler Yeats (1865–1939)
“Thyself thou gav’st, thy own worth then not knowing,
Or me, to whom thou gav’st it, else mistaking;
So thy great gift, upon misprision growing,
Comes home again, on better judgement making.
Thus have I had thee, as a dream doth flatter,
In sleep a king, but, waking, no such matter.”
—William Shakespeare (1564–1616)
“I’m going to my room now. Nobody must disturb me. Nobody, do you understand? I—I sleep during the day.”
—Griffin Jay, Randall Faye, and Lew Landers. Armand Tesla (Bela Lugosi)