The Physiology of Sleep: Function Of Sleep, Stages, Age, Cycles and Gender

Editor's Note: This article has been recently updated with latest information and research studies.
 

Our brain is not as responsive to external stimulus in the unconscious state of sleep as it is during waking hours. Sleep is triggered by the hypothalamus (the area of the brain that makes the transition from fully conscious to the slumber). It is a non arguemental fact that sleep is necessary and we are unable to function without it.

Physiological changes that occur during sleep include:

    The Physiology of Sleep
  • Cardiovascular changes occur when a person is asleep, specifically with heart rate and blood pressure. Myocardial infarction is increased upon awakening due to a spike in pressure of the blood and heart rate
  • The central nervous system relaxes* as NREM sleep deepens
  • Respiratory flow becomes erratic and quickens, especially during the REM cycle
  • Excretion of potassium, sodium, calcium and chloride is reduced* during sleep which allows urine to be concentrated
  • The Endocrine System is also affected during sleep

Stages of Sleep

There are stages of sleep that are repeated every hour and a half to two hours (90 to 120 minute cycles).

The first stage is a light sleep. This is the time when you can easily become fully awake by a disturbing noise (such as a telephone ring or a loud clap of thunder).

The next stage is when physical changes occur including a drop in body temperature. Also, your breathing will become even and rhythmical. Your mind begins to disengage itself from the current surrounding.

Finally, in this next stage your body begins to restore itself. Your muscles become relaxed and blood flow (throughout the body) increases* so any damage can be repaired and tissue growth can occur naturally. Hormones are also released during this stage of sleep, these hormones are vital for development (especially of muscle tissue). Energy that has been depleted during the day is also restored during this time so you can awake feeling rested and refreshed.

All mammals sleep in two major phases; the REM (rapid eye movement) and NREM (non rapid eye movement or also known as slow wave sleep)

Sleep Cycle

REM (rapid eye movement) and NREM (non-rapid eye movement) are the two major stages of sleep. The NREM sleep happens first and this is where your sleep becomes steadily deeper and REM sleep follows. It is in the REM sleep that our muscles are totally relaxed and eye movement is present. This is also the stage that we experience dreams.

On average, an adult has about 5 cycles of sleep per night and each cycle lasts about 60 to 90 minutes. During sleep there is a pattern that is followed, alternating between deep sleep (referred to as restorative sleep) and REM sleep (the time in which you spend dreaming). These two main stages of sleep complete the sleep cycle.

It is important to note that even though the pattern is predicable, the time spend at each stage can and will change as the evening wears on. Restorative sleep happens during the beginning of the sleep pattern and as the night goes on, the REM portion of sleep becomes longer. Because of this, it is most common to wake up during the early hours of morning instead of the first few hours that you begin the sleep cycle.

A persons biological clock also known as “circadian rhythm” is the 24 hour period that we are awake and asleep. Once night fall approaches, the body produces* a natural sleep hormone called melatonin. The sunlight limits the release of this hormone so you feel alert during daylight hours.

This natural sleep cycle can be disrupted by travel and/or nighttime work shifts leaving a person feeling disoriented, groggy and sleepy. Melatonin production can be off schedule if an individual does not get enough natural sunlight or being exposed to artificial light (especially at night) by television, computers, cellular phones and e-readers.

If you were to “chart” your sleep patterns and stages, it would resemble the skyline of a city. This is referred to as “Sleep Architecture”

Reasons We Need Sleep

There are a few different theories and facts as to why we sleep:

The first is that it is a time to rest and restore much needed energy to the body and mind and also to repair any damage to our muscles and immune system. Sleep provides* us relief* from the stresses of daily life and outside stimuli.

Sleep is needed to assist in the healing* process and boost* the immune system to help the body fight off the common cold and other diseases. Sleep also assists in energy conservation for when we need it the most.

Sleep allows us to learn more effectively and our brain has a chance to become organized. For example, memories are tucked away and unneeded information that we gathered during the day is discarded. In extensive clinical studies, problem solving became more challenging when a person was deprived of sleep. It has also been shown that REM (rapid eye movement) sleep is necessary to perform everyday tasks and our memory is dependent on “slow wave sleep”.

Sleep Requirements and Age

Sleep requirements change as we age, but never ending on more than 6 to 7 hours a sleep.

Humans start out (the first four weeks of life) requiring 16 to 17 hours of sleep within a 24 hour period and is reduced* (usually by 60 to 90 minutes) with each stage of life.

Sleep and Gender

It seems that women may sleep slightly longer than men, but not a significant amount. It does appear, through scientific study, that the sleep pattern changes in elderly women happen much later than in men. It should come as no surprise that women also dream differently than men when they sleep.

Females are prone to sleep lighter and are more susceptive to insomnia (a sleep disorder). Hormonal changes, emotions, pregnancy and menopause have a direct impact on the quality of sleep a woman receives.

Compared to working fathers, the sleep of working mothers is interrupted 2 ½ times more.

Functions of Sleep

One of the main reasons that we require sleep is repair and restores the immune system and nervous system. When proper sleep is not achieved, neurons can become clogged and polluted and they are not able to “shut down” and allow much needed restoration to happen.

Another valuable function of sleep is that it conserves our energy; sleep provides* our body and mind with time to rest so we can awaken feeling fully refreshed to face a new day and all its challenges.

From a psychological viewpoint, we sleep to give our brain a chance to relax and reorganized all the information that has been gathered during the waking state. In other words, if you are deprived of sleep, your ability to learn, retain and remember information is clouded.

In addition, sleep is helpful to remove* and forget unwanted and unnecessary information from our brains. Sleep gives our brain the opportunity to consolidate the latest information and create more “room” for more learning. This is one theory as to why brain waves are very active during slumber.

There are many “theories” as to why we sleep, some of them are backed up with scientific study and have been proven* to be true but more research needs to be done regarding the function of sleep.

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Author

Expert Author : Kelly Everson (Consumer Health Digest)

Kelly Everson is an independent editor, an award-winning writer and an editorial consultant in the health and fitness industries. Currently, she is a contributing editor at Consumer Health Digest.