• Every one has a sleep need that is likely determined by genes or genetic formation. This need is the amount of sleep our body requires for us to wake up feeling refreshed. This difference likely occurs across spectrum, with “short sleepers” needing less than average, and “long sleepers” needing more sleep.
• Every person has a natural rhythm of sleeping and waking, that is based on his daily rhythm cycle. About one-third of a person’s life is spent in this state of near unconsciousness(sleep).
What causes sleep?
• It is not known what mechanism triggers off sleep. Different theories suggest that it is due to:
1) A reduction in the amount of oxygen reaching the brain.
2) A reduction in the number of impulses reaching the conscious centres.
3) A chemical process in the brain.
4) The repeated promptings of a conditioned reflex.
5) It is also known that there are certain cell groups through out the brain which bring about sleep, when stimulated, and others that cause a sleeper to wake. A Nobel prize is waiting for any doctor or scientist who specifically pinpoints what causes sleep.
What are the daily sleep requirements for each age?
• The average amount of sleep needed changes over our lifetime, especially during childhood and adolescence. Listed below are the daily sleep requirements for each age group.
1) Infants – 3 to 11 months need 14 – 18 hours of sleep.
2) Toddlers – 12 to 35 months need 12 – 14 hours of sleep.
3) Preschoolers – 3 to 6 years need 11 – 13 hours of sleep.
4) School age – 6 to 10 years need 10 – 11 hours of sleep.
5) Adolescents – 11 to 18 years need 9 – 10 hours of sleep.
6) Adults need 7 – 8 hours of sleep.
7) Elderly adults – need less sleep 6 – 7 hours.
What are the stages of sleep?
There are two stages of sleep- 1) Orthodox sleep and 2) Paradoxical sleep(Rapid Eye Movement – REM.
1)Orthodox sleep is characterised by a fall in the heart rate, blood pressure and metabolic rate.
• Breathing is regular but slow. In light orthodox sleep, movement may occur, up to 40 changes of position at night. But in deep orthodox sleep both muscles and brain are at their most relaxed and there is no movement.
• The electrical activity of the brain becomes markedly different from the waking state. It is during this deep stage that there is a rise in the output of the growth hormone, and protein production is stepped up. The body repairs itself, and dead cells are replaced.
2) Paradoxical Sleep(REM)
• This is the stage in which dreams occur. Breathing and heartbeat become irregular, and there is Rapid Eye Movement – REM, behind the closed eyelids. Each cycle of REM takes only 90 minutes.
• The electrical activity of the brain resembles that of a waking state. Although movement may occur, the muscles are often as relaxed as in orthodox sleep, and the sleeper is just as difficult to wake.
Why do we need sleep?
• People die more quickly from lack of sleep, than they do from lack of food. A person kept awake for long periods of time, becomes increasingly disorientated, and subsequently becomes both mentally and physically exhausted.
• After 10 days of sleep deprivation death usually occurs.
What is the role of sleep in the body?
• It seems we do not sleep just because the body needs to rest. Lying down would be adequate for that. In fact the body shifts regularly during sleep, to prevent our muscles seizing up, and if we do have to do without sleep for several days, our automatic body processes can go on functioning in a fairly steady way.
• The body does not rest during sleep – but it does not seem to be sleep’s special purpose.
The brain and sleep.
• What cannot go on in a normal way, without sleep, is the brain. Lack of sleep brings irritability, irrationality, hallucinations, growing mental derangement and finally insanity, before death occurs.
• This, and the steady way body processes carry on, suggest that our feelings of physical exhaustion are also produced by the brain in its unwillingness to go on controlling the body.
• Sleep, then, “rests” the brain. But the brain’s electrical activity carries on during sleep. It certainly does not “switch-off”. So are the special deeds of the brain that are being satisfied?
What is the need to dream?
a) A famous experiment gave the answer. One group of sleepers, was woken whenever their REM sleep began, so preventing them from dreaming. They soon showed all the signs of mental disturbance.
b) Another group, woken equally but only in other stages of sleep, hardly suffered. So sleep occurs because the brain needs to dream – and when sleep is prevented, the hallucinations which eventually occur are in roughly the same pattern as dreams would occur in a sleep.
Our lesson this week – please always make out time to sleep.
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