The Brain During Sleep

Many people would be very surprised to find out exactly what happens while they are sleeping. For years people have always thought that you closed your eyes, fell asleep, your mind rested, and you had a dream. However what alot of people do not know is that while your body is resting your mind is constantly active. You see there are five different stages of sleep. Stages 1 through 4 are known as the Non Rapid Eye Movement stages (NREM) while stage 5 is known as Rapid Eye Movement sleep (REM). Now your brain will constantly cycle through these five cycles throughout the night.

Stage 1:

Stage 1 of the sleep cycle is considered to be the lightest sleep of all. This is the stage of sleep where you feel as if you are still awake however your mind and body are still drifting into a deeper sleep. This stage usually only lasts between 5 to 10 minutes and if someone is awoken during this stage they may say that they weren't really sleeping.

Stage 2:

During this phase of the cycle the body starts to enter into a deeper sleep. The brain sends you rapid waves known as sleep spindles. Your heart rate will also start to slow down and your body temperature will decrease. This stage last for approximately 20 minutes.

Stage 3:

This stage can be considered a transitional period between a light sleep and a very deep sleep. During this stage the brain starts to emit slow waves known as delta waves.

Stage 4:

Stage 4 is a very deep sleep that can sometimes be known as delta sleep due to the high levels of delta waves being emitted during this time. Stage 4 usually lasts around 30 minutes. Most cases of bed wetting or sleep walking will occur at the end of stage 4.

Stage 5:

This is the dreaming stage. Most dreams occur during stage 5 because it is known as the REM stage. REM sleep is characterized by rapid eye movement, increased brain activity, increased respiration rate. It can also be referred to as paradoxical sleep since the muscles become more relaxed even tho the brain and body are more active. Dreaming occurs due to the increased brain activity however voluntary muscles become paralyzed.

"Sleep does not progress through these stages in sequence, however. Sleep begins in stage 1 and progresses into stages 2, 3, and 4. After stage 4 sleep, stage 3 and then stage 2 sleep are repeated before entering REM sleep. Once REM sleep is over, the body usually returns to stage 2 sleep. Sleep cycles through these stages approximately 4 or 5 times throughout the night.

On average, we enter the REM stage approximately 90 minutes after falling asleep. The first cycle of REM sleep might last only a short amount of time, but each cycle becomes longer, so REM sleep can last up to an hour as sleep progresses."

Information gathered from http://psychology.about.com/