When operating properly your body’s internal clock tells you when to sleep and when to wake up. It also controls your sleep cycle stages. The scientific name for this function is known as the circadian clock. This internal mechanism controls your sleep cycle by monitoring your body temperature, hormone levels and your general level of alertness.

Behind your eyeballs are a cluster of neurons called the suprachiasmatic nucleus (SCN) that sends rhythmic signals to your pituitary gland. Your pituitary gland then sends chemicals including melatonin into your blood. Studies have found that it is the build up of melatonin that causes drowsiness.

There is another neurotransmitter, a chemical called adenosine that is produced while you are awake. Your cells produce power to get you through the tasks you need to do each day and adenosine is a bi-product of the use of that power. Adenosine builds up throughout the day to a level that tells your brain its time to sleep. The longer you resists the more adenosine and melatonin build up and you feel sleepier and sleepier until finally you have no choice but to fall asleep. While you sleep these hormones are broken down by other bodily functions and your circadian clock is reset. Then the cycle starts all over again.

Sleep Cycle Stages

The first of part of the sleep cycle is known as “relaxed wakefulness”. This is experienced right before you fall asleep and feels like that “not quite awake” and “not quite asleep” feeling. You also experience this right before you wake up in the morning. This state usually lasts somewhere between two and ten minutes and then you “fall asleep”.

Once your posture becomes relaxed you are considered to be really sleeping. Most people experience this sitting or lying down. Your muscles relax and move less. You also respond less to external stimulation such as sounds and touch and your metabolism slows down.

Scientists have divided sleep into two categories. The first is REM sleep which is short for Rapid Eye Movement. The other category is known as NREM or non REM sleep.

Non REM Sleep

The sleep cycle consists of four stages of non REM sleep sleep. The first stage or Stage I is called drowsiness. This is where your eyes move slowly and your body adjusts in the chair or bed. You sleep lightly and can be awakened easily. This transitional stage consists of about 5% of your non-REM sleep. During this sleep cycle stage your body will sometimes jerk itself awake. This is known as a hypnic jerk or hypnologic jerk. After 2 to 10 minutes you body will then start to glide off into Stage II or light sleep.

The next of the sleep cycle stages is Stage II or light sleep. You’ll spend about 45% of your non REM sleep in stage II. This is when your eye movement stops, your heart rate slows down and your body temperature drops slightly. Interestingly your brain wave levels increase.

The remaining two sleep cycle stages of non REM sleep, Stages III and IV, are known as deep sleep. In deep sleep you have no eye movement or muscle activity and are hard to wake. If you are awakened out of deep sleep you’ll feel disoriented, confused and groggy. Some people are known to act irrationally for a short while after they are awakened from deep sleep. You spend about 12% of your sleep cycle in stage III and 13% in stage IV.

REM Sleep

REM sleep is when you dream. Studies show that during REM sleep brain activity increases to nearly the same level as when a person is awake. Somewhere between 1 to 1 ½ hours after you fall asleep you enter REM sleep. During this sleep cycle stage you’ll breathe irregularly and more rapidly. Your heart rate and blood pressure rise. Men often experience erections. During REM your eyes jerk around rapidly in many directions under your eyelids. This movement is what gives REM sleep its name. Most people have three to five REM periods a night.

Wil Dieck is the founder of Total Mind Therapy and author of, “Overcoming Insomnia” an e-course you can have at absolutely no charge. Drop by http://howtosleepinfo.com/  for your copy today.