The autonomic nervous system and the role it plays in governing the behavior of the cardiovascular system is dramatic 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 parameters such as heart rate, contractility, and stroke volume 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 physiological parameters (such as heart rate and/ or smooth muscle contraction), whereas parasympathetic stimulation usually results in calming adjustments (decreased contractility and/or vasodilation). It is important to note that both branches exhibit influences that do not rigidly fit into these general guidelines.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.