Autonomic Nervous System (ANS) Sympathetic and Parasympathetic Innervations of Visceral Structures and Functioning

Abstract

Without Abstract Synonyms Vegetative nervous system; Visceral nervous system Definition The autonomic nervous system (ANS) is a part of the efferent (i.e., outgoing) division of the peripheral nervous system. It adapts the organism to internal and external changes, maintaining bodily homeostasis and coordinating bodily responses. Description The autonomic nervous system (also known as the visceral nervous system and vegetative nervous system) combines with the somatic nervous system to form the efferent (i.e., outgoing) division of the peripheral nervous system. It innervates glands, the heart, and smooth muscles of all visceral structures and adapts the organism to internal and external changes by regulating a wide range of bodily functions such as blood circulation, body temperature, respiration, and digestion. The basic tasks of the autonomic nervous system are to maintain bodily homeostasis and coordinate bodily responses. In contrast to regulatory processes of the somatic nervous The autonomic nervous system is comprised of two main branches or subsystems, (1) the sympathetic nervous system and (2) the parasympathetic nervous system. A third nervous system – the enteric system – is considered by some physiologists to be a part of the autonomic nervous system and by others to be independent of that system. The enteric nervous system consists of two large nerve networks located in the walls of the digestive tract, identified as the submucosal plexus and the myenteric plexus. It innervates the smooth muscle cells of the digestive tract as well as exocrine and endocrine cells, controlling local activity within the digestive tract (e.g., secretion of digestive juices and digestive motility). The enteric system can act autonomously, but also in response to sympathetic and parasympathetic input. Basic functional units of the sympathetic and the parasympathetic nervous systems are preganglionic and postganglionic neurons. Preganglionic neurons have cell bodies in the spinal cord or brainstem and axons that extend to cell bodies of postganglionic neurons. Postganglionic neurons have cell bodies that are clustered in so-called ganglia and axons that innervate target visceral structures. Notably, preganglionic neurons typically synapse with more than one postganglionic neuron. Similarly, postganglionic neurons typically synapse with visceral structures in multiple locations, allowing pervasive structural influence. An anatomical exception to the above is seen in the adrenal medulla. Although the adrenal medulla is a part of the adrenal gland, its cells are modified postganglionic neurons directly innervated by preganglionic neurons.