Cambridge University Press
0521845181 - The Integrative Action of the Autonomic Nervous System - Neurobiology of Homeostasis - by Wilfrid Jänig
Frontmatter/Prelims

The Integrative Action of the Autonomic Nervous System

Almost all bodily functions are dependent on the functioning of the autonomic nervous system – from the cardiovascular system, the gastrointestinal tract, the evacuative and sexual organs, to the regulation of temperature, metabolism and tissue defense. Balanced functioning of this system is an important basis of our life and well-being. The Integrative Action of the Autonomic Nervous System: Neurobiology of Homeostasis gives a detailed description of the cellular and integrative organization of the autonomic nervous system, covering both peripheral and central aspects. It brings to light modern neurobiological concepts that allow understanding of why the healthy system runs so smoothly and why its deterioration has such disastrous consequences. This broad overview will appeal to advanced undergraduate and graduate students studying the neurobiology of the autonomic nervous system within the various biological and medical sciences and will give access to ideas propagated in psychosomatic disease and alternative medicines.

Wilfrid Jänig is Professor of Physiology at the Christian-Albrechts University in Kiel, Germany.

The Integrative Action of the Autonomic Nervous System

Neurobiology of Homeostasis

Wilfrid Jänig
Physiologisches Institut, Christian-Albrechts-Universität zu Kiel, Kiel, Germany
Supported by the German Research Foundation and the Max-Planck Society

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© W. Jänig 2006

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First published 2006

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ISBN-13 978-0-521-84518-2 hardback

ISBN-10 0-521-84518-1 hardback

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Contents

Foreword

Elspeth M. McLachlan, Prince of Wales Medical Research Institute and the University of New South Wales, Sydney, NSW, Australia.

The autonomic nervous system carries the signals from the central nervous system to all organs and tissues of the body except skeletal muscle fibers. It is made up of preganglionic and postganglionic neurons linked together in functionally distinct pathways. The postganglionic terminals have specific relationships with their target tissue. As well as distributing centrally derived command signals, this system can also integrate reflex interactions between different parts of the peripheral nervous system, even without involving the spinal cord. All of these activities are specific for each organ system and attempts to generalize have often proved incorrect. The breadth and scope of involvement of this system in body function are obvious. The autonomic nervous system controls not only the quantity and quality of tissue perfusion in response to varying needs, and the maintenance of secretions for protection of the body’s orifices and the lining of the gastrointestinal tract, but it also regulates the usually intermittent but complex functions of the abdominal viscera and pelvic organs, the mechanical aspects of the eye and the communication between the nervous system and the immune system. Many autonomic pathways are continuously active but they can also be recruited when the environmental and/or emotional situation demands it. This system is essential for homeostasis – hence the subtitle of this book.

Despite its enormous importance for the maintenance of normal physiology in all vertebrate species, and for the understanding of many clinical symptoms of disease, the autonomic nervous system has not, even transiently, been the center of attention in neuroscience research internationally over the past 40 years. Many seem to think that this system has been worked out and there is nothing new to investigate. The discovery of neuropeptides as putative transmitters was probably the only interlude that triggered widespread excitement. Others simply forget that the system exists except for emergencies.

Two views about the autonomic nervous system are often encountered:

1. that this system is similar to the endocrine system and its functions can all be explained by the pharmacological actions of the major neurotransmitters, noradrenaline and acetylcholine, possibly involving modulation by cotransmitters and neuropeptides, or

2. that the functions of this system are not important as life continues without them.

For anyone who thinks about it, at least the latter of these concepts is obviously not true. Life can be maintained in a cocoon in individuals with autonomic failure but the ability to cope with external stressors severely compromises their quality of life. The extent to which the practical difficulties of daily life for people with spinal cord injury, which disrupts the links between the brain and the autonomic control of the body’s organs, absorb personal energy and resources should not be underestimated by those who take their bodies for granted. Elderly people face similar problems as some of their autonomic pathways degenerate.

On the other hand, the former of the above two concepts dominates almost all current textbooks of physiology and neuroscience. It is true that some of the effects of autonomic nerve activity can be mimicked by the application of neurotransmitter substances locally or systemically. However, the mechanisms by which the same substances released from nerve terminals produce responses in the target tissue have proved to be quite different in most cases so far analyzed. This helps to explain the failure of many pharmaceutical interventions based on this simplistic idea as outlined above. What is important here is that the present volume collates the evidence against both these ideas and develops the factual and conceptual framework that describes how an organized system of functional nerve connections that operate with distinct behaviors is coordinated to regulate the workings of the organ systems of each individual.

Nevertheless, over the past 40 years, there have been remarkable strides in our understanding. Technical problems limit how the complexities of this system can be unraveled. There are enormous challenges involved in investigating a complex interconnected system made up of small neurons that are not always packaged together in precisely the same way between individuals. Even in the spinal cord, the neuroanatomical distribution and apparent imprecision have been daunting. To study this system requires patience and persistence in the development of manipulative and analytical skills. These attributes are relatively rare.

Fortunately, over this period, a small but steady stream of researchers has persisted in their endeavors to clarify how this functionally diverse system works. One of the most significant players has been Wilfrid Jänig. Wilfrid and his many students and collaborators at the Christian-Albrechts-Universität in Kiel have pursued a major and uniquely productive approach to understanding how sympathetic pathways work. This has been to apply the technique of extracellular recording from single identified axons dissected from peripheral nerves projecting to particular target tissues and therefore acting in known functional pathways. Over the 40 years, this work, originally in cats and latterly in rats, has revealed the principles underlying reflex behavior of sympathetic axons in the anaesthetized animal. The characteristic behavior of pre- and postganglionic neurons in over a dozen functional pathways has been defined. As the reader progresses through the book, it will become clear that many of these reflexes are also present in humans. The parallel technique of microneurography, pioneered by Hagbarth, has been

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