The amount of sleep a person need
depends a lot on his age. We need less sleep, as we grow older.
Babies sleep a whole lot - about 16 or 17 hours a day! But
a 12-year-old sleeps only 9 hours; a young adult for 7 hours
and 20 minutes; and a 65-year-old, for 6 hours.
Skipping one night's sleep makes a person cranky and clumsy.
two nights of sleep, a person will have problems thinking
and doing things;
his brain and body can't do their normal tasks nearly as well.
nights without sleep, a person will hallucinate. Eventually,
impossible for the brain to give its directions to the rest
of the body
In spite of a century of scientific study of sleep, including
three decades of modern intensive research, the function of
sleep remains a biological enigma. This is not to say that
there is a paucity of theories of sleep function. On the contrary,
there are perhaps too many, given the relatively slim body
of unambiguous data that can be marshalled in support of any
one of them.
[ Restoration and Recovery
One hypothesis is that sleep serves to reverse and/or restore
biochemical and/or physiological processes that are progressively
degraded during prior wakefulness. For example: repairing
tissues and grow new cells. This classical view of sleep function
has prevailed over competing hypotheses, largely because it
is so intuitively reasonable, and especially in light of the
widespread detrimental psychological and behavioural effects
that we all experience with a loss of sleep. Also consistent
with this hypothesis is increased growth hormone secretion
immediately following sleep onset in humans which remains
synchronised with sleep even when normal sleep patterns are
inverted from nighttime to daytime. This hypothesis is not
supported by the finding of a decrease rather than increase
in protein synthesis of the whole body during sleep in humans.
The decrease in protein synthesis is attributed to sleep being
a period of overnight fasting. Consistent with the restorative
theory of sleep function are the increased amounts and "intensity"
of sleep during a period of sleep recovery after 24 hours
of sleep deprivation in humans and most other mammals.
[ Functions of R.E.M
As we go to sleep, our heart rate falls, our blood pressure
drops and our breathing becomes slow and regular. After about
20 minutes, our body usually stops shifting around and we
settle into a deep sleep called orthodox sleep. During this
stage, our muscles are relaxed and our brain activity is slowed.
It is during orthodox sleep that most the growth, maintenance,
and repair of our body occurs. This sleep is broken down into
periods of shallow sleep and REM (rapid eye movement) sleep.
There have been numerous speculations on the functions of
REM sleep, including stimulation of brain growth, fine tuning
of the binocular oculomotor system, consolidation of memory,
erasure of inappropriate memories, and the harmless discharge
of strong emotions during sleep which would otherwise intrude
into waking behaviour. There is limited evidence favouring
any one of these hypotheses.
Clearly, more research is needed before firm conclusions
can be drawn
regarding either the functions of sleep as a whole or of its
stages, but the fact that we all sleep and that there is such
drive to attain sleep suggests that it serves a vitally important
that enables us to remain alive on earth.