Nature of Sleep.

All animals sleep, therefore it is necessary for survival.
Patterns are different between species.

Newborns: Have different patterns and stages of sleep.
                   Tend to sleep for about 16 hours a day but wake every hour as their
                   sleep cycle is shorter.
                   Young babies have an initial light period of sleep.
                   Half of baby sleep is REM.
                   By 6 months a circadian rhythm should have been established.
                   By one the baby sleeps at night, with a few naps during the day.
                   REM is reduced.

Adaptive mechanism to make parents lives easier.
Waking in the night is also beneficial as they have smaller stomachs and need regular feeding.
Greater REM due to immature brains and great deal of learning takes place now.
Premature babies spent 90% of their time in active sleep.

By 5 a childs EEG is the same as an adults.
Sleep around 12 hours a night and REM takes up around 30% of this.
Boys usually sleep more than girls.

Developmental Approach: Assumes behaviour changes over a persons life span.
          Used to believe behaviour became stable at adulthood and then stopped.
Focuses on averages but individual differences are in all age groups, this can be applied to sleep.

Need for sleep increases again in adolescence to about 9-10 hours.
Their circadian rhythm also shifts so they feel more awake at night and find it harder to get up of a morning.

This change may be linked to hormones changing.
As hormones are released at night could cause sleep disruption.
Many sleep deprivation symptoms are the same as puberty; Irritability, moodiness.

Wolfson and Carskadon school should start later  (2005)

Average sleep is 8 hours a night.
REM accounts for 25% of this.
Increase in insomnia and apnoea.

Several studies have shown increased morality rate with too much sleep.
Kripke et al (2002) surveyed one million men and women and found that those slepeing for 6-7 hours a night had a reduced mortality risk compared to those who slept 8 hours, who had a 15% increased risk and those who slept 10 hours which jumped to 30%.
This is however only a correlation so can't prove a cause and effect.
It could be that illness leads to increased sleep and eventually mortality.

• Find it harder to get to sleep and wake up more.
• Have naps during the day to compensate for this.
• REM sleep reduces to 20%
• Also want to go to bed earlier and get up earlier.

 Sleep apnoea and medical illness can result in problems staying asleep in old age.
Deep sleep's reduced so they are more easily woken.
This leads to a decrease in the production of growth hormones and could explain the lack of energy and lower bone density.

Reseach into the nature of sleep has practical applications and can help to reduce the effects of ageing by improving the healthiness of sleep.

Cultural Differences-

 Tynjala (1993), Shin et al (2003) and Ghanizadeh et al (2008)
Sleep can be affected by age, cultural values and lifestyle habits i.e smoking and alcohol.