There are many theories-it has even
been suggested that sleep kept our evolutionary ancestors
safely out of harm's way during the nighttime hours
when predators roamed the landscape. However, a more
widely accepted view is that we sleep to restore our
depleted energy resources and to dissipate accumulated
wastes.
Our body is the ultimate smarty-pants.
It knows how to signal hunger and pain to us through
chemicals and electrical impulses, and sleepiness
is not an exception. Several chemical substances seem
to be associated with sleep, although none of them
has been shown conclusively to cause sleep. Analysis
of cerebrospinal fluid (the liquid that protects the
brain and spinal cord) of sleep deprived goats has
showed that it is a peptide made up of five amino
acids, including muramic acid, which is known to stimulate
the body's immune-system defenses against foreign
substances. Another sleep-producing compound, sleep-promoting
substance (SPS) has been isolated, but its chemical
composition is yet to be identified. Delta-sleep-inducing
peptide (DSIP) has also been isolated, as well as
some of the many chemicals that presumably induce
drowsiness in us when the body is in need of rest.
Foreword
