Homeostasis is the process by which
the body maintains a “steady state”
of internal conditions such as blood
pressure, body temperature, and
acid-base balance. The amount
of sleep each night is also under
homeostatic control. From the time
that we wake up, the homeostatic
drive for sleep accumulates, reaching
its maximum in the late evening when
most individuals fall asleep. Although
the neurotransmitters of this sleep
homeostatic process are not fully
understood, there is evidence to
indicate that one may be the sleepinducing
chemical, adenosine. As long
as we are awake, blood levels of
adenosine rise continuously, resulting
in a growing need for sleep that
becomes more and more diffi cult
to resist. Conversely, during sleep,
levels of adenosine decrease, thereby
reducing the need for sleep. Certain
drugs, like caffeine, work by blocking
the adenosine receptor, disrupting
this process.