Anatomy And Physiology

Our Bodies at Rest what happens when we Sleep



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Life for many of us consists of work, school, family, social life and many unexpected events that occur throughout our daily lives, keeping us busy most of the day. How many times have you thought "there is just not enough time in the day to finish everything I need to get done"? How many times have you given up some or all of your much needed sleep to finish it all? Many of us would be more than happy if we did not have to sleep at all, but this is just not possible if we want to survive and be productive each day. Our bodies have an internal rhythm or clock known as the circadian clock which regulates the way our bodies work during the day. It is made up of a tiny bundle of neurons that release melatonin, the hormone that makes us drowsy, and it is responsible for making us alert during the daytime and sleepy at night. As more of this hormone is released we get drowsy and then drift off to sleep. In addition to melatonin being released to make us drowsy, the cortisol hormone level dips at bedtime and increases over the night to promote alertness in the morning.

Giving up sleep affects every aspect of our lives including how we look, feel and perform on a daily basis, and it can have a major impact on our overall quality of life. So, what actually happens when we sleep?

Scientists can recognize different stages in sleep by tracking the changes in the brain waves during sleep. The body cycles through five stages as many as five times each night while we are asleep, so the body is quite busy during this time. To get the best benefit, we need quality sleep and enough sleep to complete all of the necessary phases for muscle repair, memory consolidation and release of hormones regulating growth and appetite. If sleep is cut short, the body cannot complete all of these phases and we are less prepared to concentrate, make decisions or engage fully in school, work or social activities during the day.

Our sleep follows a pattern of alternating REM, rapid eye movement, and NREM, non-rapid eye movement, sleep throughout a typical night in a cycle that repeats itself about every 90 minutes. As the night progresses each cycle lengthens and REM sleep, in which most dreaming takes place, extends. During the first cycle, REM lasts about 10 minutes, and lengthens a little during each cycle until it lasts about an hour.

As we fall asleep we enter NREM, non-rapid eye movement sleep, which consumes about 75% of the night and is composed of four stages.

Stage One

During this stage we are between being awake and falling asleep. The brain waves slow and the body drifts off to sleep.

Stage Two

During this stage our heartbeat and breathing slows down, we become disengaged from our surroundings, body temperature drops and sleep is deeper than in stage one.

Stages Three and Four

These are the stages in which sleep is the deepest and most restorative. Breathing and heartbeat slow further and muscles relax allowing our bodies to repair and restore itself for the next day. During these stages our blood pressure drops, the blood supply to the muscles increases, tissue growth and repair occurs, energy is restored and hormones, such as growth hormone, are released for growth and development. Our brain waves are the slowest during this stage.

As the night progresses and REM increases breathing becomes more shallow and eyes move rapidly, muscles are relaxed and dreams are most vivid. REM consumes about 25% of the night and it first occurs about 90 minutes after falling asleep and recurs about every 90 minutes.

This cycle provides energy to the brain and body and supports daytime performance. The brain is active and dreams occur, the eyes dart back and forth beneath the eye lids and the body becomes immobile and relaxed as the muscles are turned off.

Sleep helps us thrive by contributing to a healthy immune system and can also balance our appetites by helping to regulate levels of the hormones ghrelin and leptin, which play a role in our feelings of hunger and fullness. So when we are sleep deprived, we may feel the need to eat more, which can cause weight gain.

We spend one-third of our lives sleeping, and though it may seem we are being unproductive during such a large part of our lives, our sleep has a direct effect on how full, energetic and successful the other two-thirds of our lives can be.

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