|What is Sleep?
Sleep is a natural state of rest characterized by reduced body movement and decreased awareness of surroundings. Sleep is distinguished from other sleeplike states, for instance, hibernation or coma, because it is easily interrupted by external stimulation, such as a loud noise. While the exact purpose of sleep remains a mystery, sleep researchers have made enormous strides in understanding how sleep occurs in humans and other animals, and the nature of sleep disorders. So it isn't just what happens when they put a sheet over your cage or am I alone on this one?
Just for Reference:
NREM (Non Rapid Eye Movement) Sleep: Normal deeper sleep in which the blood pressure, pulse, and muscle tension in the body all go down.
REM (Rapid Eye Movement) Sleep: Sleep closely associated with consciousness because of high brainwave activity. Characterized by the twitching of the eyes.
Stages of Sleep
Stage 1: This is the first stage of sleep. It's the gateway to deeper sleep. You can easily be awakened from this stage of sleep. It's when you're just falling into unconsciousness. You can very easily awakened from this stage, which is why we refer to it as the "gateway" to deeper sleep - you can't get any rest if you're disturbed out of this stage. Clinical tests prove that this is the time in which it is most likely that the neighbors will begin fighting or a dog will begin barking uncontrollably.
Stage 2: Should you make a few threatening phone calls to your neighbors and throw a few blunt objects at the dog across the street and make it through stage one, you'll enter stage two. Stage two is much deeper than stage one. It is the stage in which hypnogogic imagery first begins to make itself apparent. It's much harder to be awakened from than stage one.
Stage 3: This is a very deep stage of sleep. Your muscles relax, and your heart rate slows. Your blood pressure begins to fall, and your breathing becomes steady and even. You're far gone into sleepytown by now. Nuclear war couldn't wake you. You can, however, be awakened by loud noise (which, actually, I'd imagine nuclear war entails), repeated calling out of your name, or physical stimuli (i.e. your roommate poking you in the forehead with a ruler).
Stage 4: This is the closest you're going to get to dead without being there. This is the deepest stage of sleep there is. You dream here. They can take a sledgehammer to your face and you'll stay fast asleep. Very little can wake you now. You'll need to be shaken or you'll need to hear a very loud noise, and even then, you take several seconds to fully awaken. Your heart rate and blood pressure fluctuate, and your brain begins to heat up. Most important of all, Rapid Eye Movement (REM) takes place during this stage. This REM is, some say, what gives you renewed vitality in the morning. In other words, how much sleep you think you got, might be dependent upon the amount of REM sleep you get. You usually dream during REM. The first REM period will last about ten minutes, then the sleeper will go back into a normal deep stage four sleep. Then, he will cycle into another REM period and then back into regular stage four sleep. This pattern will continue until the sleeper awakens (or is awakened).
So? I Want to Be Ready For My Next Party. Do Lizards Sleep or Not? Well, here you are. No, they do not. At least, not that we know of. All mammals and birds do sleep, though. Larger mammals tend to sleep less than smaller ones, though. The giraffe and elephant, for instance, sleep only 2 to 4 hours a day, while bats, opossums, and armadillos sleep 18 hours a day or more.
Okay. That's Fine. But What If The Guest Of Honor Wants To Know What Position Giraffes Sleep In? Well, not to worry. Giraffes kneel and bend their long necks around to rest their heads in the crook of their hind knee. In fact, most animals close their eyes and adopt particular positions referred to as sleep postures. Humans typically lie down to sleep. Some animals, such as dolphins, can sleep while they are moving, which explains Al Gore's unique personality (I'm kidding, I'm kidding, I'm a Democrat, put your weapons away). Scientists measure sleep by placing metal electrodes on the scalp to record the electrical activity of the brain. I know. It's as fun as it sounds, trust me. This procedure, called electroencephalography (EEG), enables sleep researchers to evaluate levels of brain activity at different times during sleep. Researchers use similar electrodes to record a sleeping person's body muscle activity and rate of eye movement.
Stages of Sleep
What is Sleep