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Sympathetic nerve - Definition


A sympathetic or orthosympathetic nerve belongs to the sympathetic nervous system, which in turn is part of what is called the autonomic or vegetative nervous system. This system is comprised of nerve fibers that primarily innervate organs of the chest cavity or abdomen, with automatic control of their activities. The sympathetic nervous system functions with the help of two chemical mediators: adrenalin and noradrenalin, which enable an increase or reduction, depending on which receptor they affect, in the strength of involuntary functions, in particular that of blood vessel constriction or dilation, increased cardiac rhythm, and relaxation of certain involuntary muscles. Sympathetic nerves are frequently stimulated when the body is being attacked, particularly in order to adapt to systemic consequences by increasing blood pressure and the force of heart contraction, as well as prioritizing blood supply to what in the past were called the "noble" organs, such as the heart and brain.