Chapter 12 - Autonomic Nervous System Physiology

A specialized taxonomy of the autonomic nervous system (ANS) has been developing since the time of Galen (ad 130200). In the early 1900s, Langley first referred to the ANS. He used the term sympathetic nervous system (SNS) as described by Willis in 1665, and introduced the second division as the parasympathetic nervous system (PNS) in 1921. Although Langely initially described only the visceral motor system (efferent fibers), the existence of visceral reflex arcs necessitated the inclusion of the sensory (afferent) portions of the ANS. Early anesthesia textbooks dealt with the practice of anesthesia, elucidating basic considerations, pharmacology and techniques, but did not contain explicit information dealing with the ANS. The evolution of the comprehensive anesthesia textbook has led to extensive chapters on the ANS. The ANS maintains cardiovascular, thermal, and gastrointestinal homeostasis. A firm understanding of the basic anatomy and physiology of the ANS forms an important foundation for the practice of anesthesiology. ANS structure, function, and reflexes are critical to the support of the circulation under anesthesia. This chapter reviews anatomy and physiology of the ANS relevant to anesthesia.