Anatomy And Physiology

Anatomy Physiology

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What happens when we sleep? This questions has plagued scientists and confused the lay person alike. We know that we need sleep. We know that during sleep our body's cells repair themselves, growth hormones are released, our minds processes information, and we re-energize. We know without sleep our cognitive thinking is poor. We can hallucinate. Our minds fail. We are susceptible to disease and are cranky. What we don't know is why...

Here is an overview of what we know occurs during sleep and four theories that researchers have devised trying to explain why we do need sleep.


Stage 1 Stage 1 is the time it takes for an individual to actually fall asleep. An average adult spends only 5 percent of their sleeping time in this stage. Our brain waves are high amplitude slow waves and we have occasional alpha waves, which are normally found while we are awake. This is the lightest cycle of sleep and we are often awoken by slight noises or movement.

Stage 2 During this step, our heartbeat and breathing slow. Sleep is deeper than in stage 1. Slow wave sleep occurs with peaks in brain waves, which are referred to as sleep spindles. Our bodies begin to relax in this stage. A normal adult spends 44-55 percent of their time in this stage.

Stage 3 and 4 These two stages are when we are deepest in sleep. Here, our brainwaves are the slowest. Our heartbeat slows and muscles relax completely. This is normally the stage where people sleepwalk. At this stage our bodies operate with a mind of their own and our minds release control. An average adult will spend 15-23 percent of their time in these two stages.

Stage 5 (REM) REM sleep stages lengthen throughout the course of the night. Although your first REM cycle may be only 10 minutes long, your last REM cycle could last up to an hour. At this stage, breathing becomes shallow, heartbeat increases, muscles relax and your eyes may move. Dreams are most vivid and prominent in this stage. Your brain waves closely resemble your brain waves when you are awake. This is the stage that memories and thoughts throughout the day are regarded. Our minds sift through them and decide which memories are keepers that we file away, and which are forgotten. An average adult will spend about 20-25 percent of their sleep time in this stage.

Different studies have shown what the effects of not getting a good night's sleep are. According the American Cancer Society, people who do not get an average of 7-8 hours per sleep a night have a 30% higher death rate. Just 17 hours of being awake, and our bodies start to shut down. In fact sleepiness has the same effect on our bodies as drinking. Staying awake for 17 hours straight is the equivalent as drinking 2 glasses of wine.

Sleep allows our bodies to recuperate, improves immunity, helps us think more clearly and operate soundly. It also restores mental health. Although scientists realize that sleep is essential for survival, there is no set theory about why we do sleep, or need it. There are four basic theories that scientists have devised for why we need sleep.


This theory states that humans and all animals acquire sleeping habits to enhance their likelihood of survival. This theory explains why some animals are nocturnal.

To survive, animals, and humans in early years needed high metabolic rates to outrun enemies and capture food. Sleeping was a way to re-energize and conserve energy. It was also a way to rebuild our bodies for the next day's survival.

This theory tends to be most popular in scientific communities. This theory states that during sleep our bodies restore and replenish. During non-REM sleep, neurotoxins are stabilized, cells divide, tissues synthesize, and growth hormones are released. For this reason, children and young adults spend more time in non-REM stages because their bodies are not done growing.

Researchers suggest that sleep holds the key to memory. Unimportant information is "erased" during sleep while pertinent information is stored during REM sleep. Babies who tend to be learning the most sleep the most. Babies, young adults, children, and people who are in school or undergoing training spend more time in REM cycles. If people are deprived of sufficient REM sleep their problem solving skills are less developed.

In conclusion, although scientists are divided on exactly why we need sleep, everybody concludes that we do in fact need sleep. Sleep deprivation equals slower responding time, increased risk of infection and death, and lower cognitive though.


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