In mammals, the part of the nervous system 
that controls the involuntary activities of
the smooth muscles (of the digestive tract,
blood vessels), the heart, and the glands. 
The sympathetic system responds to stress,
when it speeds the heart rate, increases 
blood pressure and generally prepares the
body for action.  The parasympathetic system
is more important when the body is at rest,
since it slows the heart rate, decreases
blood pressure, and stimulates the digestive
system.

Subject by: Russell Webb