Simply put, from the point of view of our experience, sleep is turning off the outside world.
But sleep is also quite complicated.
Let's look at how we fall asleep and move through the different stages of sleep.
Your body begins to prepare for sleep the moment the sun goes down.
As the levels of light diminish the pineal gland begins to secrete more and more melatonin.
Melatonin is often referred to as the body's primary sleep hormone.
The rising level of melatonin has a calming and soothing effect.
Recall a time when you went camping.
You may have sat in the dark in front of a fire with thousands of stars overhead.
The crackling and warmth of the fire has an entrancing effect, taking your mind off your worries.
The darkness (the melatonin) coaxes you to sleep.
Falling Asleep Once in you are in your warm sleeping bag, your mind begins to drift and you begin to forget about the outside world.
You are now entering Stage 1 sleep.
The faster alpha waves of the full waking state are replaced by slower theta waves.
At the same time your body eases into a more relaxed state.
Your breathing begins to slow, your heart beat becomes more regular and your blood pressure begins to decrease.
The blood flow to your brain and your brain's temperature also start to decline.
At this stage you can be awakened easily, and you may even feel that you never really got to sleep.
Light Sleep Over the next 15 to 20 minutes, you descend into Stage 2 sleep.
If your brain were monitored, it would now show a new set of characteristic brain waves.
Your senses continue to disengage from the external environment and at this stage you would not awaken as easily.
If someone were to push back an eyelid, you would be oblivious to the outside world, seeing nothing.
But a sound in the room might still awaken you.
Most of your body organ systems continue to slow down (lowered blood pressure, heart rate, muscle tension, body secretions).
Deep Sleep About 30-45 minutes after falling asleep, your brain wave patterns change again, and for the first time the delta waves of deep sleep emerge.
You are now moving into Stages 3 and 4 of deep sleep.
(Stage 3 and 4 are distinguished from each other only by the amount of Delta wave activity measured in the brain.
Together they are called deep sleep.
) At this point it would take a lot more effort to wake you up-only loud noises and some jostling could awaken you.
If you are awakened from sleep at this stage you may be groggy, even confused or disoriented, as if drunk from sleep.
You may not be able to function normally for some time.
Sleep walking, sleep talking or bed wetting usually occur during deep sleep.
At this stage of sleep your body's systems have slowed to the deepest state of physical rest.
The Rejuvenating Effects Of Deep Sleep While in deep sleep your body replenishes and repairs itself.
At this stage the hypothalamus (part of the brain) signals the anterior pituitary gland at the base of the brain to increase secretion of human growth hormone (HGH).
(HGH is sometimes referred to as the hormonal "fountain of youth" because of its ability to restore adult bodies to a more youthful state.
In children it promotes tissue building and growth.
)As your body cycles in and out of deep sleep through the rest of the night, additional spurts of HGH are released.
During deep sleep the overall metabolic activity of the brain decreases.
Rapid Eye Movement Sleep (REM) After a period of deep sleep, your brain waves shift again and your eyes begin to flutter back and forth under closed eyelids.
You are now dreaming, having moved into what is referred to as REM sleep (for Rapid Eye Movement).
REM sleep has been shown to be essential for integrating recent experiences into memory.
During REM sleep there is an increase in blood flow to certain areas of the brain.
These areas include the areas that process visual stimuli, and information from our senses.
This may explain the vivid nature of the dreams we often experience.
Blood flow to the prefrontal cortex which governs our ability to evaluate and analyze experience remains decreased during REM sleep.
This could explain why when we're dreaming we accept the most bizarre dream content.
Sleep Cycling Through the rest of the night you continue to cycle through stages II, III and IV of unconscious sleep, then back into dreaming with Rapid Eye Movement three to four more times.
With each cycle of sleep, as you move into deeper sleep your brain releases surges of human growth hormone to restore and repair my body.
This is followed by more dreaming, helping your brain to integrate your recent experiences into memory and knowledge.
Preparing For Daytime Activity As the light of the dawn begins to reveal that morning is approaching, your brain stops producing as much melatonin.
But how is that possible? After all your eyes are closed.
Researchers have found that the brain responds to light on the skin.
When researchers shined light on the back of the knee of volunteers they were able to measure significant changes in the circadian rhythm of the brain.
That is the light stimulated changes in our brains biological clock.
Numerous other hormonal changes occur in early morning hours before we awaken.
One of the key shifts is the rise in cortisol.
The brain begins to signal the pituitary gland which in turn instructs the adrenal glands to release cortisol.
Cortisol mobilizes our energy stores and raises blood sugar.
This increased supply of blood sugar is the fuel our brain, our internal organs and our muscles need to get us going when we wake up.
The Insomnia Stress Connection We said that the brain signals the brain to wake up in the morning with a message to the adrenal glands.
The adrenal glands secrete cortisol which raises blood sugar.
The adrenal glands are part of the body's stress response.
The same brain sequence which wakes up up in the morning also functions (with slight variations on a theme) during stress.
Cortisol rises whenever your body becomes stressed.
With stress there are also local hormonal changes within the brain.
The purpose of the stress response is prepare you for activity and to maintain your alertness.
The stress response was meant to help us to deal with temporary crises.
When the crisis is over the stress response ends, the body de-stresses and the levels of stress hormones revert to normal.
With the chronic stresses of modern life, we tend to have higher levels of stress hormones all the time.
Since the function of stress hormones is partly to keep you alert, they can also keep you alert at night.
That is they keep you awake and prevent you from going to sleep.
In fact, stress is the most common cause of insomnia.
But sleep is also quite complicated.
Let's look at how we fall asleep and move through the different stages of sleep.
Your body begins to prepare for sleep the moment the sun goes down.
As the levels of light diminish the pineal gland begins to secrete more and more melatonin.
Melatonin is often referred to as the body's primary sleep hormone.
The rising level of melatonin has a calming and soothing effect.
Recall a time when you went camping.
You may have sat in the dark in front of a fire with thousands of stars overhead.
The crackling and warmth of the fire has an entrancing effect, taking your mind off your worries.
The darkness (the melatonin) coaxes you to sleep.
Falling Asleep Once in you are in your warm sleeping bag, your mind begins to drift and you begin to forget about the outside world.
You are now entering Stage 1 sleep.
The faster alpha waves of the full waking state are replaced by slower theta waves.
At the same time your body eases into a more relaxed state.
Your breathing begins to slow, your heart beat becomes more regular and your blood pressure begins to decrease.
The blood flow to your brain and your brain's temperature also start to decline.
At this stage you can be awakened easily, and you may even feel that you never really got to sleep.
Light Sleep Over the next 15 to 20 minutes, you descend into Stage 2 sleep.
If your brain were monitored, it would now show a new set of characteristic brain waves.
Your senses continue to disengage from the external environment and at this stage you would not awaken as easily.
If someone were to push back an eyelid, you would be oblivious to the outside world, seeing nothing.
But a sound in the room might still awaken you.
Most of your body organ systems continue to slow down (lowered blood pressure, heart rate, muscle tension, body secretions).
Deep Sleep About 30-45 minutes after falling asleep, your brain wave patterns change again, and for the first time the delta waves of deep sleep emerge.
You are now moving into Stages 3 and 4 of deep sleep.
(Stage 3 and 4 are distinguished from each other only by the amount of Delta wave activity measured in the brain.
Together they are called deep sleep.
) At this point it would take a lot more effort to wake you up-only loud noises and some jostling could awaken you.
If you are awakened from sleep at this stage you may be groggy, even confused or disoriented, as if drunk from sleep.
You may not be able to function normally for some time.
Sleep walking, sleep talking or bed wetting usually occur during deep sleep.
At this stage of sleep your body's systems have slowed to the deepest state of physical rest.
The Rejuvenating Effects Of Deep Sleep While in deep sleep your body replenishes and repairs itself.
At this stage the hypothalamus (part of the brain) signals the anterior pituitary gland at the base of the brain to increase secretion of human growth hormone (HGH).
(HGH is sometimes referred to as the hormonal "fountain of youth" because of its ability to restore adult bodies to a more youthful state.
In children it promotes tissue building and growth.
)As your body cycles in and out of deep sleep through the rest of the night, additional spurts of HGH are released.
During deep sleep the overall metabolic activity of the brain decreases.
Rapid Eye Movement Sleep (REM) After a period of deep sleep, your brain waves shift again and your eyes begin to flutter back and forth under closed eyelids.
You are now dreaming, having moved into what is referred to as REM sleep (for Rapid Eye Movement).
REM sleep has been shown to be essential for integrating recent experiences into memory.
During REM sleep there is an increase in blood flow to certain areas of the brain.
These areas include the areas that process visual stimuli, and information from our senses.
This may explain the vivid nature of the dreams we often experience.
Blood flow to the prefrontal cortex which governs our ability to evaluate and analyze experience remains decreased during REM sleep.
This could explain why when we're dreaming we accept the most bizarre dream content.
Sleep Cycling Through the rest of the night you continue to cycle through stages II, III and IV of unconscious sleep, then back into dreaming with Rapid Eye Movement three to four more times.
With each cycle of sleep, as you move into deeper sleep your brain releases surges of human growth hormone to restore and repair my body.
This is followed by more dreaming, helping your brain to integrate your recent experiences into memory and knowledge.
Preparing For Daytime Activity As the light of the dawn begins to reveal that morning is approaching, your brain stops producing as much melatonin.
But how is that possible? After all your eyes are closed.
Researchers have found that the brain responds to light on the skin.
When researchers shined light on the back of the knee of volunteers they were able to measure significant changes in the circadian rhythm of the brain.
That is the light stimulated changes in our brains biological clock.
Numerous other hormonal changes occur in early morning hours before we awaken.
One of the key shifts is the rise in cortisol.
The brain begins to signal the pituitary gland which in turn instructs the adrenal glands to release cortisol.
Cortisol mobilizes our energy stores and raises blood sugar.
This increased supply of blood sugar is the fuel our brain, our internal organs and our muscles need to get us going when we wake up.
The Insomnia Stress Connection We said that the brain signals the brain to wake up in the morning with a message to the adrenal glands.
The adrenal glands secrete cortisol which raises blood sugar.
The adrenal glands are part of the body's stress response.
The same brain sequence which wakes up up in the morning also functions (with slight variations on a theme) during stress.
Cortisol rises whenever your body becomes stressed.
With stress there are also local hormonal changes within the brain.
The purpose of the stress response is prepare you for activity and to maintain your alertness.
The stress response was meant to help us to deal with temporary crises.
When the crisis is over the stress response ends, the body de-stresses and the levels of stress hormones revert to normal.
With the chronic stresses of modern life, we tend to have higher levels of stress hormones all the time.
Since the function of stress hormones is partly to keep you alert, they can also keep you alert at night.
That is they keep you awake and prevent you from going to sleep.
In fact, stress is the most common cause of insomnia.
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