Physiologic Effects of Sleep
Sleep causes two major types of physiologic effects: first, effects
on the nervous system itself, and second, effects on other functional systems
of the body. The nervous system effects seem to be by far the more important
because any person who has a transected spinal cord in the neck (and therefore
has no sleep-wakefulness cycle below the transection) shows no harmful effects
in the body beneath the level of transection that can be attributed directly to
a sleep-wakefulness cycle.
Lack of sleep certainly does, however, affect the functions of the
central nervous system. Prolonged wakefulness is often associated with
progressive mal-function of the thought processes and sometimes even causes
abnormal behavioral activities.
We are all familiar with the increased sluggishness of thought that
occurs toward the end of a prolonged wakeful period, but in addition, a person
can become irritable or even psychotic after forced wakefulness. Therefore, we
can assume that sleep in multiple ways restores both normal levels of brain
activity and normal “balance” among the different functions of the central
nervous system. This might be likened to the “rezeroing” of electronic analog
computers after pro-longed use, because computers of this type gradually lose
their “baseline” of operation; it is reasonable to assume that the same effect
occurs in the central nervous system because overuse of some brain areas during
wakefulness could easily throw these areas out of balance with the remainder of
the nervous system.
We might postulate that the
principal value of sleepis to restore natural balances among the neuronal
centers. The specific physiologic functions of sleepremain a mystery, and
they are the subject of much research.
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