Autonomic Nervous System

The autonomic nervous system (ANS) serves as the body’s intrinsic control system governing the behaviors of the cardiovascular and pulmonary systems: having significant roles in modulating physiologic activities so as to adapt to daily stressors or conserve bodily functioning. The hypothalamus is the brain’s autonomic control center, which governs all essential “homeostatic” functions of the human body. Its integrative functions include: modulating the ANS, activation of various somatic pathways, and the regulation of the body’s hormonal systems. The autonomic nervous system can be considered to have two subdivisions that are considered antagonistic but also function in a complementary nature; simultaneous changes within the parasympathetic and sympathetic branches of this system allow for rapid and essential changes in cardiac parameters such as heart rate, contractility, and/or stroke volume. Increased sympathetic outflow relative to normal resting conditions most often causes an excitatory response in physiologic parameters (such as increases in heart rate and/or smooth muscle contraction), whereas parasympathetic stimulation usually results in calming adjustments (lower heart rates, decreased contractility, and/or vasodilatation). Alterations of the cardiac and aortic baroreceptors, as well as the autonomic nerves that innervate the heart, are important to consider in many disease states.