Therapy Analysis - Sleep, A Mental Mystery
Why do we sleep?
Having seen how we sleep, the next obvious question is why, though this is still yet to be conclusively answered. There are two general theories that try to explain this: firstly, that sleep gives the body necessary recuperative time after the activities of the day; and secondly, that vital physiological process and activities occur during this time for growth, development and general metabolic 'housekeeping'.
The body is 'programmed' to sleep and to do so at particular times of the day. When we are awake we accumulate high levels of adenosine, as the day's activities require the catabolism of ATP to provide cellular energy. These high levels of adenosine are thought to be a major cause in giving rise to feelings of drowsiness, and as such have also been linked to the cause of jet lag. The cycles of biological processes that occur between sleep give rise to the 'circadian rhythm'. This rhythm is largely regulated by a small group of cells called the suprachiasmatic nucleus (SCN), often referred to as the internal biological clock, located in the hypothalamus, just above the crossing of the optic nerves. When light stimulates the photoreceptors in the retina, signals are carried back to the SCN, as well as other regions of the brain. At particularly low levels of light, the signals received by the SCN travel to the pineal gland, which stimulates the secretion of melatonin, causing the onset of sleep. During sleep the circadian rhythms induce the decrease in heart and breathing rate and the secretion of growth hormones, melatonin and cortisol.
Researchers such as Jim Horne of Loughborough University, the UK, and Dr. Michael Jouvet of Claude Bernard University, France, have indicated that the brain uses sleep to sort information gathered from the day to fill in some long-term memory and it is essential to maintaining normal levels of cognitive skills such as speech. It has also been stated that hormones that stimulate growth in tissues and bones are released in larger doses during slow-wave sleep. It is clear that sleep does have a physiological function, but the particulars of this function remain largely unknown.
Perhaps one of the best and oft-tried ways to gain understanding of why we need to sleep is to observe the effects when sleep is withheld. When someone is deprived of sleep they will experience increasing mental and physical fatigue, often becoming irritable, groggy and forgetful. Sleep deprivation studies, headed by researchers at the University of Chicago, have found that severe lack of sleep has associations with the inability to metabolise glucose as hormones and chemicals controlling appetite and weight gain are released as we sleep, potentially leading to conditions such as Type II diabetes and obesity. Further studies have also revealed that sleep deprivation interferes with many other body processes including wound healing, cognitive function, growth and other day-to-day activities. Patients and volunteers in sleep deprivation studies at the UCSD School of Medicine experienced a range of symptoms including hallucinations, hypertension, paralysis, delirium, depression and weakened immune systems, all as a result of the lack of sleep.
Sleep being such a crucial part of healthy life means that there exist many ailments which are linked directly to sleep or the lack thereof. Insomnia, of course, the inability to achieve or maintain satisfactory sleep, is very common and most people will experience it at least once in their lifetime. However, there are a variety of less common but still debilitating diseases related to sleep. Narcolepsy, classified as excessive daytime sleepiness, is a sleep-related disorder which affects 1 in every 2,000 people. It is characterized by the sudden onset of muscle weakness (sleep paralysis) and the induction of sleep at unintended times, often due to strong emotions. This condition is associated with the ineffective control of REM.
Another common sleep disorder is sleep apnoea, characterised by interruptions in breathing during sleep and estimated to affect 1 in 15 of the population. The muscles in the throat relax, obstructing the airways, and causing one or more breaths to be missed. This condition can potentially prove fatal, and often remains undiagnosed for years, with the patient remaining unaware of the sleep disturbance and becoming used to the daytime fatigue that results. A primary contributory cause of sleep apnoea is obesity, and so a great deal of success in patients can be achieved by treatment of this factor. The most common method of treatment is known as 'continuous positive airway pressure', which involves using a mask during sleep pushing pressurised air into the lungs, effectively forcing the airways to stay open.
Periodic limb movement disorders (PLMD) such as restless leg syndrome (RLS) are sleep-related disorders characterised by repetitive cramping or jerking of the legs during sleep, interrupting sleep and leading to sleepiness during the day. RLS differs from PLMD (although 80% of RLS patients have PLMD) due to the patient's experience of strange and uncomfortable sensations in their limbs resulting in an uncontrollable urge to move, stretch or shake their arms or legs. This condition has associations with Parkinson's disease, iron deficiency, diabetes, rheumatoid arthritis and sleep apnoea, and affects 5-10% of adults in Western countries.
