REM sleep is (rapid eye movement) it occurs in brief spurts of increased activity in the brain and body. REM is considered the dreaming stage of sleep and is characterised by the rolling of the eyes under the eyelids.
NonREM is a state of sleep that is characterised by four stages that range from light dozing to deep sleep. 75% of sleep is spent in NREM.
One main researcher Oswald (1970) suggested that both REM and NREM sleep is needed to restore us both physiologically and psychologically. He suggested that NREM sleep is needed more to restore bodily processes so a relinquish of energy as it has been used up during the day and that REM sleep is when neurochemicals that have been used up in the day are regenerated by protein synthesis.
We can break down restoration into two parts psychological restoration is mainly dealing with insomniacs these are sleep problems that are characterised by difficulty in falling asleep this is more clear to see by looking at the symptoms of jet lag. The symptoms are thought to be caused by the releases of the hormone melatonin which is out of step with the environment the person now finds themselves in. This results in drowsiness during the day and insomnia during the night.
The second part of restoration is physiological restoration this is shown by the sleep pattern of babies and foetuses they spend an average of 18hours a day sleeping and use about half of the 18hours in REM sleep. This is opposed to 8 hour sleep that adults have and they spend about a quarter of that in REM sleep. This shows the larger amount of brain activity that occurs in developing brains and a lot of protein synthesis is needed for cell and synaptic growth. From this both physical and brain protein synthesis are dependant on growth hormones which are secreted after the first bit of delta activity in slow wave sleep.
The second theory is the evolutionary theory this has two parts to it the conservation part and the protection part. Meddis (1979) suggested that in order for animals to protect themselves they would sleep and this would increase there chances of safety as the animals would be immobile and therefore would be less likely to be noticed by predators.
An example of this would be the sleeping pattern of dolphins. The dolphins in the River Indus only sleep for a few seconds at a time repeatedly through 24 hours. Marine dolphins only sleep with one hemisphere at a time showing that they do this to protect themselves from predators, the theorist Webb (1982) supported the view that sleep helps to conserve energy but also thought it allowed animals to become more aware of an able to avoid predators.
Apart from looking at marine animals it’s clear to see animals that graze such as sheep need little sleep as they are vulnerable and need to eat in order to gain energy and also it makes them more vigilant as they are moving about a lot more and can attract the attention of predators.
Animals that hunt are at little risk from predators for example lions these need lots of sleep as this is away to keep them safe and conserve a lot of energy.
The evolutionary theory can be directly linked to Darwin’s theory of ‘survival of the fittest’ as any properties we have now are a result of what has been useful in the past therefore we sleep as it has been useful for our survival or it was at one time.
Conservation was an idea that the theorist Webb came up with he suggested that those animals that slept more were more likely to survive such as hedgehogs. Conservation is where the body slows down the metabolism and heart rate as no food is being consumed and no energy is being used up as the animal is not moving about. Webb’s theory is linked to hibernation mostly as his theory is more suggesting the likelihood of surviving due to sleeping.
By looking at both theories I can now come to the conclusion that the restoration theory is more logical in its use of energy as it suggests that the more energy you use up in the day the more you look forward to going to bed to restore tissue and save energy.
It also suggests that even if you don’t fully exert yourself in a day it doesn’t mean that your not going to sleep for long and this can be fully evident in teenagers as even if they do or don’t exert themselves they still sleep a lot more as there bodies are developing and they need more sleep then the rest to gain in energy and also to give there bodies a time to relax as there bodies will be constantly secreting hormones.
The cause and effect of insomnia still aren’t clear as the Pineal gland in the brain converts the neurotransmitter serotonin into the hormone melatonin. Melatonin is released into the blood stream and causes rhythmic changes around the body although the need for sleep is not affected by light. Melatonin plays a role in the co-ordination of the sleep wake cycle. So as sleep isn’t affected by light then the cause of insomnia can’t be known as you can’t determine what effects the body that causes insomnia.
REM sleep involves an increase in energy expenditure and blood flow which inhibits protein synthesis on the other hand it is known that amino acids are not stored by the body and last in the body for bout 4 hours after a meal. This means that protein synthesis maybe stopped half way through sleep because the amino acids have run out.
Also people will sleep more after stress and it is known to improve moods which again can be explained by the fact that with NREM sleep occurring during slow wave so enables the body to repair itself and there is an increase in secretion of growth hormones.
By looking at the evolutionary theory I can also conclude that the arguments presented for the evolutionary theory contradict themselves as some suggest that some animals sleep less to keep a vigil while others suggest that animals sleep longer to keep motionless thus staying away from harm.
Also it is clear to see that animals such as lions do sleep longer as they are at less of a risk from being hunted so don’t need that much sleep and animals like cattle need very little sleep and this puts them in danger of being hunted.
