It's a universally accepted fact that everyone needs sleep. But why do we need sleep and what happens to our bodies as we are sleeping?
There are two kinds of sleep states - the famous REM (rapid eye movement) state, also known as the dream state of sleep, and the non-REM state of sleep, which is also known as slow wave' sleep. In non-REM sleep, there are 4 stages. Stage 1 is the dozing' stage, where you're falling in and out of sleep. Your body's physical signs are about the same as if you are awake. In Stage 2, you're in a light sleep, and your body temperature begins to drop (that's why falling asleep in the heat is often difficult). In Stages 3 and 4, deep slumber will have set in, and your mind and body are at rest. Your blood pressure is down, your breathing slows and your muscles relax. It is also during this stage that your metabolism will drop significantly, but at the same time, hormones that help tissues and bones grow and regenerate will be released in higher doses. Perhaps this is where the old saying, a growing boy needs his sleep' comes from. Speaking of hormones, studies have shown that sleep helps to regulate the body's production of the hormone leptin, which helps tell us whether we're full or hungry. Those that don't get a lot of sleep often feel hungrier, leading them to eat more.
Children get more slow wave sleep than adults, especially in stages 3 and 4. This may explain why it's hard to wake a sleeping child even with loud noises or moving them (to their cribs, or from a car to bed). They also do not wake up as much during the night as adults.
REM sleep is the dream state of sleep, and it is here that the body becomes immobile, as muscles are temporarily paralyzed, which prevents people from acting out whatever it is they're dreaming. Those who sleepwalk often have an impairment that prevents the body from effectively paralyzing the muscles while in the REM state. During REM, the body is truly at rest, but paradoxically, the brain begins to awaken, and is actually at its most active. REM sleep can only be achieved after a person has gone through some slow wave sleep. In other words, you're not going to fall asleep and instantly begin dreaming. Usually, it takes about 90 minutes to cycle through a sleep cycle (both slow wave and REM), but REM sleep is more frequent in the last few hours of sleep.
As fascinating as all of this information about sleep states may be, it still does not answer the question, why do we need sleep? And the short answer is, we don't know.' Scientists have theories about it, but none have been proven conclusively. The older theories postulate that sleep helps the brain to consolidate information, and/or the refuel and purge all the stimuli it was inundated with during the day. This certainly makes sense when you consider that those who get little sleep often become sluggish and their mental acuity diminishes greatly. A new theory emerged in the 1990's that, in its simplest terms, state that sleep may help your brain learn new tricks. Studies that dealt with procedural memory (learning repetitive tasks) show that those that slept on it' often performed better.
So how much sleep do we need to let our bodies and brain do all of this? There's no definitive answer, but perhaps the common sense approach would work best here. If you feel tired or sluggish the next day, find it hard to concentrate, and wake up still feeling sleepy, perhaps you're not getting enough sleep.