McKenna's Pharmacology for Nursing, 2e

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C H A P T E R 2 9 Introduction to the autonomic nervous system

CHAPTER SUMMARY ■■ The autonomic nervous system (ANS) works with the endocrine system to regulate internal functioning and maintain homeostasis. The two parts of the ANS, the sympathetic nervous system (SNS) and the parasympathetic nervous system, work in opposition to maintain minute-to-minute regulation of the internal environment and to allow rapid response to stress situations. ■■ The SNS, when stimulated, is responsible for the fight-or-flight response. It prepares the body for immediate reaction to stressors by increasing metabolism, diverting blood to big muscles and increasing cardiac and respiratory function. ■■ The parasympathetic system, when stimulated, acts as a rest-and-digest response. It increases the digestion, absorption and metabolism of nutrients and slows metabolism and function to save energy. ■■ The SNS is composed of CNS cells arising in the thoracic or lumbar area of the spinal cord, short preganglionic axons, ganglia located near the spinal cord and long postganglionic axons that react with effector cells. The neurotransmitter used by the preganglionic cells is acetylcholine (ACh); the neurotransmitter used by the postganglionic cells is noradrenaline. ■■ One SNS ganglion on either side of the spinal cord does not develop postganglionic axons, but instead secretes noradrenaline directly into the bloodstream to travel throughout the body to react with adrenergic receptor sites. These ganglia evolve into the adrenal medulla. ■■ SNS adrenergic receptors are classified as being alpha 1 -, alpha 2 -, beta 1 - or beta 2 -receptors based on the effectors that they stimulate. ■■ ACh is made by choline from the diet and packaged into storage vesicles to be released by the cholinergic nerve into the synaptic cleft. ACh is broken down to an inactive form almost immediately by acetylcholinesterase. ■■ The parasympathetic system comprises CNS cells that arise in the cranium and sacral region of the spinal cord, long preganglionic axons that secrete ACh, ganglia located very close to or within the effector tissue and short postganglionic axons that also secrete ACh.

■■ Noradrenaline is made by adrenergic nerves using tyrosine from the diet. It is packaged in storage vesicles that align on the axon membrane and is secreted into the synaptic cleft when the nerve is stimulated. It reacts with specific receptor sites and is then broken down by MAO or COMT to relax the receptor site and recycle the building blocks of noradrenaline. ■■ Parasympathetic system receptors are classified as muscarinic or nicotinic, depending on what response they have to these plant alkaloids.

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ONLINE RESOURCES

An extensive range of additional resources to enhance teaching and learning and to facilitate understanding of this chapter may be found online at the text’s accompanying website, located on thePoint at http://thepoint.lww.com. These include Watch and Learn videos, Concepts in Action animations, journal articles, review questions, case studies, discussion topics and quizzes.

BIBLIOGRAPHY

Barrett, K. E. & Ganong, W. F. (2010). Ganong’s Review of Medical Physiology (23rd edn). New York: McGraw-Hill. Davis, G. (2007). The central, peripheral and autonomic nervous system: An overview. Nurse Prescribing, 5(1) , 16–21. Goodman, L. S., Brunton, L. L., Chabner, B. & Knollmann, B. C. (2011). Goodman and Gilman’s Pharmacological Basis of Therapeutics (12th edn). New York: McGraw-Hill. Guyton, A. & Hall, J. (2011). Textbook of Medical Physiology (12th edn) . Philadelphia: Saunders Elsevier. McCorry, L. K. (2007). Physiology of the Autonomic Nervous System. American Journal of Pharmaceutical Education, 71(4) , 78. www.ncbi.nlm.nih.gov/pmc/articles/PMC1959222/. Porth, C. M. (2011). Essentials of Pathophysiology: Concepts of Altered Health States (3rd edn). Philadelphia: Lippincott Williams & Wilkins. Porth, C. M. (2009). Pathophysiology: Concepts of Altered Health States (8th edn). Philadelphia: Lippincott Williams & Wilkins. Robertson, D., Biaggioni, I., Burnstock, G., Low, P. A. & Paton, F. R. (2012). Primer on the Autonomic Nervous System (3rd edn). London: Elsevier.