Autonomic nervous system

Abstract

The autonomic nervous system and the role it plays in governing the behavior of the cardiovascular system is immense in both its complexity and importance to life. The antagonistic nature of the parasympathetic and sympathetic branches of this system allows rapid and essential changes in cardiac parameters such as heart rate, contractility, and stroke volume in order to deliver metabolites and nutrients to tissues and organs that need them at any given time. Increased sympathetic outflow relative to normal resting conditions most often causes an excitatory response in physiologic parameters (such as heart rate and/or smooth muscle contraction), whereas parasympathetic stimulation usually results in calming adjustments (decreased contractility and/or vasodilatation). It is important to note that both branches exhibit influences that do not rigidly fit into these general guidelines. © 2009 Humana Press.