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Section 1: Epidemiology and aetiology.
We spend one-third of our lifetime asleep, yet scientists are only now beginning to learn about the complexity of the neuroanatomical/neurochemical networks of sleep and the genetics of the sleep-wake cycle.
For 10-15 per cent of adults the biological state of sleep is disturbed, leading to impaired psychological, cognitive and physical functioning.
Sleep is an active process. The sleep-wake cycle of humans is slightly longer than 24 hours and has to be entrained to a 24-hour cycle. This is achieved by behaviours such as the time we go to school, work, eat, and so on. However, the two most important entrainers of the cycle are light and melatonin, with a negative feedback loop.
When the suprachiasmatic nucleus in the hypothalamus receives the light signal via the photopigment melanopsin in the retina, responsive to short wavelength (blue) light, there is suppression of secretion of melatonin from the pineal gland.
As the environmental light decreases in the evenings, melatonin starts to be secreted, followed by fall in core body temperature, conducive to sleep.2
A number of hormone secretion cycles are closely related to sleep, including growth hormone, which peaks in the early part of sleep, and cortisol, which peaks at the end of night sleep.
The two well-recognised sleep states are non-rapid eye movement (NREM) sleep, alternating in 90-minute cycles with the more primitive rapid eye movement (REM) sleep.
In general, physiological parameters, such as heart rate, respiration and BP, fall in NREM sleep and are relatively unstable in REM sleep.
Insomnia is the most common sleep complaint in primary care; 10-15 per cent of referrals to sleep centres are for insomnia.
ICSD 2 Classification of sleep disorders1
- Sleep-related …