Discuss The Nature Of Sleep

Discuss the nature of sleep ( AO1= 8, AO2=16)
In this essay I will discuss the nature of sleep, in terms of: REM, NREM, and the physiology of sleep.
There are two sorts of sleep: REM and NREM. REM and NREM are as different from each other as each is from wakefulness. NREM sleep is characterised by an idle brain in a very relaxed body; whereas REM sleep is characterised by a brain that appears to be wide awake in a virtually paralysed body. There are 4 stages to NREM sleep: ‘falling’, easily woken is the 1st stage. Second stage is responsive to external stimuli. Third stage is difficult to wake, and the 4th is deep sleep, which is occasionally characterised by sleep walking in some individuals. It has been found that younger people sleep more than older ones; it’s also true that babies spend far more time than REM sleep; up to 50% of their sleep is REM. Young adults spend about 20% of sleep in REM and elderly adults only about 15% in REM. This is supported by Zimbardo et al; and further support is given by Okai et al who found a correlation between sleep changes and development of the brain. However there are very few studies on school age children and adolescents and on middle year’s adults, so this lack of data means that little that is useful can be concluded about those age groups.
The American Academy of Sleep Medicine suggests the daily hours of sleep for an infant is much higher than compared to adults; infants spend 14-15 hours whilst adults spend 7-8 hours. This is supported by Armstrong et al, who found daytime sleep becomes less regular as age increases, and also found there’s a wide variation of normal early childhood sleep behaviour. These findings suggest that childhood sleep behaviour shows variation as it mirrors human variation in general, particularly adult behaviour. Similarly, Armstrong et al also found circadian rhythms aren’t well established until 4 months of age, suggesting the development of the rhythm could be well be in line with early brain development and growth. This is supported by Harrison, who found infants exposure to light promoted the development of their circadian sleep rhythm. However, Armstrong’s study provides weak evidence because it’s only carried out on Australian children, so cannot be generalised to the whole population, and therefore lacks population validity.
The stereotype of elderly people often includes frequent dozing. This is supported by Foley et al who found napping in the elderly has been positively correlation between excessive daytime sleepiness and depression. However, this study provides weak evidence because it is a correlational study, so a cause and effect cannot be established. On the other, a contrasting study, which surveyed 2000 women, found normal sleep with no perceived sleep problems was linked to healthy aging, so older women who slept well were less likely to suffer from mood, attention, or memory problems.
Also, we have 5 cycles of sleep which occur for 90 minutes during an average night’s sleep. This supported by Jouvet who believes these cycles of sleep occur as a result of the relationship between the raphe nuclei and locus coeruleus, which generate the NREM and REM cycle.
Evolutionary functions of sleep is supported by Meddis, who found sleep keeps ‘prey safe’ from preditors, which suggests the patterns