It is defined in the Stedmans Medical Dictionary as "A physiologic state of relative unconsciousness and inaction of the voluntary muscles, the need for which recurs periodically". Totora & Grabowski in Principles of Anatomy and Physiology add that "it is a state of unconsciousness from which a person can be aroused; associated with a low level of activity in the reticular activating system".

Sleep and waking are two opposite states of being which compete for consciousness. Wakefulness is maintained by the Reticular Activating System. (RAS) assisted by the catecholaminergic and cholinergic transmitter systems. Sleep is promoted by the activity of the dorsal raphe which acts with other structures to deactivate the RAS. Serotonogenic neurons dampen down sensory activity and inhibit motor activity during sleep - promoting slow wave activity of the cortex. (Culebras 1992)

The reticular activating system (RAS) comprises parts of the medulla oblongata, the pons and midbrain and receives sensory input from the auditory and vestibular aparatus; the eyes, and somatosensory impulses (nocioreceptors, proprioceptors and touch receptors). When the reticular formation (that is, the parts of the RAS) are active, nerve impulses pass upward to widespread areas of the cerebral cortex, both directly and via the thalamus effecting a generalised increase in cortical activity associated with waking or consciousness. The RAS does not receive input from the olfactory nerves (sense of smell) - hence people do not awaken with the smell of smoke during a fire.

Our individual cycles of sleep are closely tied to our circadian rhythms, or daily variations in physiology including body temperature. These rhythms are aligned to our environment, and vary with the season as well as throughout the life cycle. Many creatures possess a pineal gland, which scientists believe to be a kind of 'natural clock', helping us to synchronise our activities with nature. In humans, the pineal gland is a tiny pine-cone shaped gland attached to the roof of the third ventricle deep within the brain and weighs between 0.1-0.2 grams.

The pineal gland helps govern our circadian rhythms, those biological rhythms which take place over a 24-hour day, such as the sleep-wake cycle. It uses melatonin, a hormone secreted by the pineal gland during sleep - normally 'the dark' cycle of the day, as a messenger to communicate with these other systems via the suprachiasmatic nucleus of the hypothalamus. Melatonin production is inhibited by light and the release of norepinephrine - an important neurotransmitter, which is why something as innocuous as the LED of your electric alarm clock could actually be disrupting your sleep. The pineal gland then, helps control what time we eat and rest, our production of natural hormones, changes in body temperature, our immune system and many other body functions, and may be one of the reasons why it feels "natural'' to sleep at night. It coordinates and controls our other hormone-release and immune responses.

As we grow older, from about middle age (35) onwards, our sleep tends to become less and less deep, and this factor appears to be directly related to reduction in melatonin production. Deep sleep is the stage when our body healing, repair and regeneration occurs. These latter stages of the sleep cycle are crucial times for physical recovery and psychological well being. It is also when the body secretes the most growth hormone, amongst other chemicals.

It is the quality of sleep that influences our physical, psychological and social well being, and many people suffer from a sleep disturbance which may be comprised of a broad range of problems.

An interrupted sleep cycle with insufficient Rapid Eye Movement (REM) Periods of sleep can be at root of many physical and psychological effects such as fatigue, inability to concentrate, dizziness, perceptual changes and mood changes. Many sleep disorders cause an increase in daytime sleepiness and there is a direct correlation to an increase in motor vehicle accidents.

The sleep disorders have been connected to attentional and cognitive deficits, which are most commonly observed in the areas of attention and tasks of high level integration such as solutions of problems in arithmetic. Studies have shown that improvements of sleep patterns lead to improvements in function and cognition.

Dement and Klietman (1957) classified sleep into four distinct stages:
Stage 1 Sleep or onset is characterised by low voltage random EEG activity. This is the transitionary stage between wakefulness and sleep and last between 1 and 7 minutes. (People wakened at this stage of sleep will often say that they have not been sleeping).
Stage 2 Sleep or light sleep is categorised by an irregular EEG pattern with 12-14 Hz (alpha) "sleep spindles" and the "K complex" - a 75uV burst of EEG activity. This is really the first stage of 'true' sleep. The person is a little more difficult to awaken. Here, fragments of dreams may be experienced, and the eyes may slowly roll from side to side.
Stage 3 Sleep shows alternate fast activity, low voltage waves and large slow waves (delta - 0.5-3.0 Hz). This is a period of moderately deep sleep which occurs approximately 20 minutes after first falling asleep. Body temperature and blood pressure decrease, and the person is difficult to awaken.
Stage 4 Sleep is comprised of the "K complex" wave and is present in more than 50% of the epoch (20-30 seconds of unit measurement). This is the deepest level of sleep. Most reflexes are intact, although the person will respond very slowly upon awakening. When sleepwalking occurs, this is the stage that it does so. Here we find REM or the Rapid Eye Movement stages followed by Non-REM (NREM) - which comprises a combination of stages 1,2,3 & 4 but no rapid eye movements.

Typically, the person goes from Stage 1 to Stage 4 NREM sleep in less than an hour. A person has 3-5 episodes of REM sleep in each 7-8 hour sleep period, and the autonomic nervous system becomes more active during REM sleep. It has been found that during REM, our brain uses up to 20% more oxygen - more than it does during intense physical activity while awake.

REMs were found to be associated with vivid dreaming (Aserinsky and Klietman 1953). The presence of REMs alone is not sufficient to denote the presence of dreaming, but the activity appears to coincide with the emergent stage 1 of a new sleep cycle.

A person goes through these stages of sleep many times a night, and a full cycle - from stage 1 back to stage 1 again takes approximately 90-100 minutes (Dement and Klietman 1957), but stages 3 and 4 occur more rarely as sleep progresses. That is, the person sleeps more lightly as the end of the sleep period approaches. Dreaming then, occurs approximately four times per night, and if awakening occurs during the REM Stage, we remember our dreams.

It is interesting to note that researchers have observed that the newborn infant spends around 50% of its time in REM, and premature infants as much as 75%. A child of 2 years has 35% REM sleep, whilst an adult usually has around 25%. The higher proportion of REM sleep in infants is thought to be important for brain maturation.

Over a prolonged period, lack of REM sleep can cause serious illness and premature ageing. Most important in maintaining quality REM sleep throughout the lifetime is maintaining consistency and regularity of the sleeping period - getting into the habit of retiring at a specific time each night and awakening (without the use of an alarm clock ideally) at a specific time each morning.

Day time sleep differs from night time sleep, but a permanent night work schedule appears to allow the body to adjust.

Sleep has been studied extensively by researchers and clinical research has revealed that there are more than 80 sleeping disorders. Some of the more common ones are listed below.

Many people resort to prescription or over the counter sleeping medications and preparations, but these do not cure sleeping disorders, and they interfere with the quality of REM sleep. There are natural solutions to these common and debilitating sleep disruptions, and by enhancing your sleeping hours naturally, your waking ones will improve as well. 

Symptoms of Obstructive Sleep Apnea (OSA) are listed below.

Intervention for Restless Legs Syndrome and Periodic Limb Movements is highly effective for 90 percent of patients seeking help.

Parasomnia refers to a wide variety of disruptive, sleep-related events or "disorders of arousal." These arousal disorders include:

Children are subject to sleep disorders too and they can be affected at many levels. The disorder(s) themselves may be indicative of other problems.

There are many natural interventions which can help people to sleep better. These include counselling, guidance and education, dietary guidelines, nutritional supplements, SAMONAS Sound therapy (via bone conduction for sleep apnoea), EEG Biofeedback and Alpha-Theta, Hypnotherapy, CranioSacral and Bowen therapy, Bach Flower remedies and aromatherapy. Different combinations of the above interventions devised to cater for individual needs have been successful with a range of sleeping problems.

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