Hi all,
Thanks for the excellent discussion! I haven't read such good
spirited discussion on internet for quite some time.
Since one can not keep taking without giving back, I will chip
in my two cents:
I believe the basic function of sleep is to stop the
fully-awake cycle and start a maintenance cycle. The Hypothalamus
determines when sleep is needed:
(a) To refresh the body: human body generates many waste and
some of them are poisonous if not clean up in timely fashion.
Hypothalamus monitors the contents of blood and orders
a maintenance cycle should body is in bad shape. This is
when a sick patient starts to feel sleepy.
(b) To refresh the brain: as a special case to (a), the brain
is often the first components of the body that signals the
need for a maintenance cycle. The brain consumes the majority
of energy and blood supply in normal condition. A high school
student often feels sleepy due to heavy homework.
(c) To refresh the memory: as a special case to (b), the memory
encoding/retrieval is heavy part of the overall consciousness
process in brain. The cortex that dominates the memory and
thinking process is the prefrontal lobe, it consumes most of
the blood supply and energy of the brain. Thus it is often the
first components in the brain that triggers the signal for a
maintenance cycle.
The maintenance cycle is signified by a 7-13 Hz alpha wave.
It may not actively clean up the neuron, but it does help
inhibit the neuron and send them back to initial state.
(d) To calm the emotion: as another special case to (b), the
emotion system (limbic) is also part of the consciousness.
The limbic system causes emergency reaction and results in
consuming large amount of blood supply and energy. The
consequence is also signals for the need of maintenance
cycle after the emotional reaction.
However trying to sleep after an emotional event is very hard
since many neurons are fired up to the fullest and is
extremely hard to tame them with the alpha wave. Sleeping pill
is often needed in these cases.
(e) To preserve energy: Even if none of the above occurs, the
hypothalamus has an internal biological clock to mandate
the 'wake' and 'sleep' cycle. It is normally coincide with
the 'day' and 'night' cycle to preserve energy when there is
nothing to do.
In modern society this biological clock is often disturbed by
the artificial light. Many young people stay up all night
dancing until cases a-d arises.
We still have a lot to learn in this subject. Again, thanks
for the excellent dialog!
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