how does overall sympathetic or parasympathetic nervous system control effect blood pressure
Sympathetic nervous system Messages travel through the sympathetic nervous system in a bi-directional flow. Efferent messages can trigger changes in different parts of the body simultaneously. For example, the sympathetic nervous system can accelerate heart rate; widen bronchial passages; decrease motility (movement) of the large intestine; constrict blood vessels; increase peristalsis in the oesophagus; cause pupillary dilation, piloerection (goose bumps) and perspiration (sweating); and raise blood pressure. One exception is with certain blood vessels such as those in the cerebral and coronary arteries, which dilate (rather than constrict) with an increase in sympathetic tone. This is because of a proportional increase in the presence of β2 adrenergic receptors rather than α1 receptors. β2 receptors promote vessel dilation instead of constriction like α1 receptors. An alternative explanation is that the primary (and direct) effect of sympathetic stimulation on coronary arteries is vasoconstriction followed by a secondary vasodilation caused by the release of vasodilatory metabolites due to the sympathetically increased cardiac inotropy and heart rate. This secondary vasodilation caused by the primary vasoconstriction is termed functional sympatholysis, the overall effect of which on coronary arteries is dilation.[9]