Sleep is a state of altered consciousness or partial unconsciousness from which an individual can be aroused by many different stimuli. Prolonged wakefulness or sleep deprivation causes fatigue plus it lowers the immune system, increasing both the urge to sleep and the deepness of sleep once it occurs. Also reoccurring illness can be a product of sleep deprivation as can mood swings and erratic behaviour patterns.

insomniaAlthough the exact triggers for sleep are still unclear, several lines of evidence suggest the existence of sleep-inducing chemicals in the brain. One apparent sleep-inducer is adenosine, which accumulates during period of high ATP (adenosine triphosphate) use by the nervous system. Adenosine binds to specific receptors, called A1 receptors and inhibits certain cholinergic (acetylcholine-releasing) neurons of the RAS that participate in arousal. Thus activity in the RAS during sleep is low due to the inhibitory effect of adenosine. Caffeine (in coffee) and theophylline (in tea) substances known for their ability to maintain wakefulness bind to and block the A1 receptors, preventing adenosine from binding and inducing sleep.

Just as there are different levels of awareness when a person is awake there are different levels of sleep. Normal sleep consists of 2 components: non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep. NREM sleep consists of four gradually merging stages each of which is characterized by a different kind of EEG activity.

1. Stage 1 – is a transition stage between wakeful ness and sleep that normally lasts 1-7 minutes. The person is relaxed with eyes closed and has fleeting thought. People awakened during this stage often say that they have not been sleeping. Alpha waves which are present in people awake with eyes closed diminish and are replaced by lower frequency, slightly larger amplitude EEG waves.

2. Stage 2 or light sleep- is the first stage of true sleep. In it a person is a little more difficult to awaken. Fragments of dreams may be experienced and the eyes may slowly roll from side to side.

3. Stage 3 is a period of moderately deep sleep. Body temperature and blood pressure decrease. It is difficult to awaken the person and the EEG shows a mixture of sleep and larger lower frequency waves. This stage occurs about 20 minutes after falling asleep

4. Sage 4 or slow-wave sleep is the deepest level of sleep. The person responds slowly if awakened and the EEG is dominated by slow large amplitude Delta waves. Although brain metabolism decreases significantly during slow-wave sleep and body temperature drops slightly most reflexes are intact and muscle tone is decreased only slightly. When sleepwalking occurs it does so during this stage.

Typically a person goes from stage 1-4 of NREM sleep in less than an hour. During a typical 7-8 hour sleep period there are 3 to 5 episodes of REM sleep during which the eyes move rapidly back and forth under closed eyelids. The person may rapidly ascend through stage 3 and 2 before entering REM sleep. The first episode of REM sleep lasts 10-20 minutes and is followed by another interval of NREM sleep.

Most dreaming occurs during REM sleep and the EEG readings are similar to those of an awake person. With the exception of motor neurons that govern breathing and eye movements most somatic motor neurons are inhibited during REM sleep which decreases muscle tone and even paralyse the skeletal muscles. Many people experience a momentary feeling paralysis if they are awakened during REM sleep.
The autonomic nervous system becomes more active during REM sleep heart rate and blood pressure increase. In men autonomic excitation causes erection of the penis during most REM intervals even when dream content is not sexual. Presence of penile erections during REM sleep in a man with erectile dysfunction (inability to attain an erection while awake) indicates a psychological rather than a physical cause of his problem.

REM and NREM sleep alternate throughout the night. REM periods which occur approximately every 90 minutes gradually lengthen until the final one lasts about 50 minutes. In adults REM sleep totals 90-120 minutes during a typical sleep period. AS a person ages the average total time spent sleeping decreases: moreover the percentage of REM sleep declines. AS much as 50% of an infant’s sleep is REM sleep as opposed to 35% for a 2 year old and 25% for adults.
Although we do not yet understand the function of REM sleep the high percentage of REM sleep in infants and children is thought to be important for the maturation of the brain. Neuronal activity is high during REM sleep-brain oxygen use is higher during REM sleep than during intense mental or physical activity while awake.

imagesNO LIGHT
The importance of sleeping in total darkness at night to optimise the production of melatonin. Melatonin is a cancer preventing hormone that helps you sleep and also contributes to the timing of the biological clock of the body. The effects of artificial light on the brain at night can be detrimental to your health. The eyelids even when closed are translucent and allow waves of photic stimulation to travel deep into the pineal gland in the brain.

The illuminated faces of bedside clocks, red charge lights from beside phones, T V and computer screen left on standby during the hours of sleep and light from street lamps and children’s night lights, will enter the eye through the closed lids, strike the retina and stimulate the photo receptors.

The chemical chain reaction continues, ultimately inhibiting the production of melatonin by the cells of the pineal gland. This could in part lead to hyperactivity in children and severely disrupted sleep patterns in adults with possible severe mood swings and behavioural changes. A few simple strategies can help prevent light at night entering the eyes:

 Cover the windows with dark lined curtains or blinds, to cut out the light from street lamps
 Switch off computers and TV’s in the bedroom at night when sleeping
 Cover clock faces and phone chargers with a piece of material
 Shut the bedroom door and cover the cracks if a light is left on in the hall
 Train small children to sleep without a night-light


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