Sympathetic Control
Known as the "fight or flight" mechanism the sympathetic
nervous system originates in the thoracic and lumbar regions of
the spinal cord. Most postsynaptic sympathetic nerve endings
release 
adrenaline or
norepinephrine. Sympathetic 
stimulation of
the heart has two effects: (1) it increases the heart rate (250
bpm with maximal stimulation); and (2) it increases the force of
contraction which decreases the duration of systolic contraction
and allows more time for filling during diastole. The innervation
of the small arteries and arterioles allows sympathetic
stimulation to increase the resistance thereby changing the rate
of blood flow through the tissues. The innervation of the 
large
vessels (particularly of the veins) makes it possible for
sympathetic stimulation to change the volume of these vessels and
alter the volume of the peripheral circulatory system. This can
translocate blood into the heart, thus playing a major role in
the regulation of cardiovascular function.
adrenaline or
norepinephrine. Sympathetic 
stimulation of
the heart has two effects: (1) it increases the heart rate (250
bpm with maximal stimulation); and (2) it increases the force of
contraction which decreases the duration of systolic contraction
and allows more time for filling during diastole. The innervation
of the small arteries and arterioles allows sympathetic
stimulation to increase the resistance thereby changing the rate
of blood flow through the tissues. The innervation of the 
large
vessels (particularly of the veins) makes it possible for
sympathetic stimulation to change the volume of these vessels and
alter the volume of the peripheral circulatory system. This can
translocate blood into the heart, thus playing a major role in
the regulation of cardiovascular function.