Functional Neuroscience

Transcription

1 Functional Neuroscience

2 Springer Science+Business Media, LLC

3 Oswald Steward, Ph.D. Reeve-Irvine Research Center University of California, Irvine Functional N euroscience with 306 Illustrations, 89 in color Springer

4 Oswald Steward, Ph.D. Reeve-Irvine Research Center University of California, Irvine 1105 Gillespie Neuroscience Research Facility Irvine, California USA Library of Congress Cataloging-in -Publication Data Steward, Oswald. Functional neuroscience / Oswald Steward. p. cm. Includes bibliographical references. ISBN ISBN (ebook) DOI / Neurosciences. 1. Title. [DNLM: 1. Nervous System Physiology. 2. Nervous Systemphysiopathology. 3. Nervous System-anatomy & histology. WL 102 S849f 1998] RC341.S dc21 DNLMIDLC for Library of Congress CIP Printed on acid-free paper Springer Science+Business Media New York Originally published by Springer-Verlag New York, Jnc. in 2000 AU rights reserved. This work may not be translated ar copied in whole or in par! without the written permis sion of the publisher Springer Science+Business Media, LLC, except for brief excerpts in connection with reviews ar scholarly analysis. Use in connection with any form of information storage and retrieval electronic adaptation, computer software, ar by similar ar dissimilar methodology now known or hereafter developed is forbidden. The use of general descriptive names, trade names. trademarks, etc., in this publication, even if the former are not especially identified, is not to be taken as a sign that such names, as understood by the Trade Marks and Merchandise Marks Act, may accordingly be used free1y by anyone. While the advice and information in this book are believed ta be true and accurate at the date of going to press, neither the authors nor the editors nor the publisher can accept any legal responsibility for any errors ar omissions that may be made. The publisher makes no warranty, express or implied, with respect to the material contained herein. Production coordinated by Impressions Book and Journal Services, Inc., and managed by Lesley Poliner; manufacturing supervised by Jacqui Ashri. Typeset by Impressions Book and Journal Services, Inc., Madison, W ISBN SPIN

5 To Kathy, Jessie, and Ossie

6 Preface This book is designed to be used as the core neuroscience text for medical students. It presents the key information that is required for a basic understanding of the operation of the nervous system. My goal in writing this text was to integrate and blend two successful styles. One is the style that has dominated the neuroanatomical teaching known as "functional neuroanatomy", in which the focus is on regional anatomy, and how lesions at particular sites disrupt different pathways. The second is the style favored by neurophysiologists known as "systems neuroscience" in which the focus is on the physiological operation of the different functional systems. I use the term "functional neuroscience" to refer to the resulting blend. The overall organization of the presentation, as reflected by the chapter headings, is traditional. We begin by considering the ground plan of the nervous system (that is, regional anatomy and the organization at different levels of the neuraxis). Then, we consider cellular aspects of neuroscience, focusing first on the basic cell biology of neurons and glia, and then on signaling processes. In this, I have made certain choices that reflect the way the medical curriculum is organized in most medical schools. For example, there is no chapter that covers resting membrane potential and action potential, or the elemental aspects of synaptic transmission. These topics are usually taught in the physiology courses in most medical curricula. The present book assumes a background in these subjects, and then moves on to those aspects of synaptic transmission that are especially important for neurons in the central nervous system (that is, integration of information from multiple inputs, interactions between different kinds of neurotransmitter systems, and integration of excitation and inhibition). The third section of the book is the heart of what I call functional neuroscience. In this section, each of the key functional systems are considered one by one. We begin with the somatosensory pathways, and vii

7 viii PREFACE then consider the motor pathways and sensory motor integration. The reason for considering somatosensory and then somatomotor is that the two are mapped in parallel throughout the neuraxis, and there important function interactions between sensory and motor components at each level. We then consider the systems that control the output of the somatic motor pathways, the cerebellum and the basal ganglia, and follow with a consideration of the special senses: vision, audition, vestibular system, and the chemical senses (taste and smell). The final section considers the systems that mediate associative and integrative functions, and the "higher" functions mediated by the cerebral cortex. Some instructors who are used to the "functional neuroanatomy" style may be surprised that there is no separate chapter on the cranial nerves. Instead cranial nerves belonging to a particular functional system are described in the chapter pertaining to that system. The cranial nerves that are involved in somatic sensation are described in the somatosensory section; the cranial nerves that control the muscles of the face are described in the motor system, and the cranial nerves that control autonomic functions are described in the chapter on the autonomic nervous system, and finally there is a separate chapter that considers the control of eye movement. This book is designed for medical students. I have attempted to keep the presentation as concise as is consistent with accuracy. There is minimal consideration of original data, and the only references are the ones indicated as sources for the figures. The cost of maintaining brevity is that I do not cite the thousands of individuals whose research forms the basis of the material presented herein, or provide a view of how the knowledge was actually derived. Also missing is a consideration of the limitations of our present knowledge. For this reason, instructors will need to provide supplementary material for graduate students or medical students interested in neuroscience research. How TO ApPROACH THE SUBJECT OF NEUROSCIENCE The information that is encompassed by Functional Neuroscience is of critical importance to physicians of all types. The importance of the information to a specialist is obvious, however, family physicians must also use this information on virtually a daily basis. Whenever a patient walks into your office for whatever reason, you will be carrying out a basic neurological exam. This means observing the patient for any signs and symptoms suggestive of disease of the nervous system. When you first see the patient, you check for general demeanor. When you shake their hand, you check their hand strength. You watch their eyes to detect any abnormalities in eye movement. You observe how they hold themselves in order to detect any postural asymmetries. You listen to what they say to detect any difficulties with speech or difficulties with cognition. Part of your routine neurological exam will involve watching your patient move across the room. This will give you an initial indication of their motor status. You will likely do a simple check of reflexes, and you may carry out simple tests of eye movements to track visual stimuli. You may ask to the patient to stand with their eyes closed to check their balance, to touch their nose or ear with their eyes closed, to rapidly pat the back and front of their hands to check for cerebellar function. And then of course, you will listen to what the patients say about any problems they are experiencing. Everything that you learn in this way is then integrated into an opinion about the patient's functional situation. If you detect no abnormalities, and in the absence of any complaints from the patient, you will conclude that their nervous system is functioning normally. Any complaints, however minor, will cause you to formulate hypotheses about what may be wrong. The important question that you must ask yourselves is, "is there a lesion involving the nervous

8 PREFACE ix system, and if so where is it localized?". The answer to these questions will tell you whether you handle treatment yourself or refer the patient to a specialist. Learning neuroscience is a challenge. One reason is that it is difficult to begin by presenting the "big picture" and then move to the details. Instead, in most cases one can't understand the big picture without knowing the details. Usually it is not until the end of the course that all the pieces start to "come together". This causes anxiety. The most important advice I can give is, be patient. The big picture will eventually become clear. The other difficulty is in the nature of the information that must be learned. Physicians must understand the pathways that mediate particular functions. One must be able to predict the site of a lesion on the basis of a certain symptom complex, and one must be able to predict the symptoms from a known lesion. This requires integration of a variety of types of information. Students must also learn about the way signaling occurs in the nervous system. This is a different kind of information, more conceptual in nature than the memorization required to know where a particular pathway lies. Some students excel at learning one type of information, others excel at learning the other. It may help to recognize individual differences in order to focus one's efforts for maximal efficiency. One important aspect of neuroscience is that one can't learn something and then put it aside to move on to something else. At each stage, students must make use of information learned at earlier stages. This becomes apparent when trying to understand the consequences of lesions at particular sites. To understand the consequences of a lesion involving the brain stem, one must know the distribution of the somatosensory pathways, the motor pathways, the organization of the cranial nerve nuclei, the descending autonomic pathways, and the functional role that the cerebellum plays in modulating motor output. The big picture comes from the details. This type of learning is challenging and sometimes frustrating, but IS what you need to know. An important skill that physicians must develop is the ability to identify structures from histological sections, CT scans, or magnetic resonance images (MRI). This skill requires an understanding of regional neuroanatomy and three-dimensional structure. In this regard, memorization of a particular photograph or drawing is not sufficient, since any section or image may be taken at a slightly different angle or magnification. One must be able to generalize in order to recognize structures in configurations that have not previously been seen. Although sections and diagrams are included in this book, the full development of the ability to identify structures will require practice with a variety images. Students are encouraged to explore image-based self-study programs which are available by subscription, or to use any of a number of human brain atlases.

9 Acknowledgments I would like to thank two colleagues have played an especially important role in shaping my philosophy regarding the teaching of neuroscience. The first is Edwin R. Rubel, formerly of the University of Virginia, and now at the University of Washington. Dr. Rubel's lectures on sensory systems were my first exposure to what I now call functional neuroscience. The second key colleague is Dr. Gary Banker who directed the neuroscience course at the University of Virginia, and was a master in the "functional neuroanatomy" style. Both of these individuals as well as other colleagues as the University of Virginia will certainly detect elements of their own teaching style in this book. The original drawings and diagrams in this book are the work of a single artist, Ms. Ann Dunn. I would like to acknowledge her creativity and her tolerance for the uneven schedules, and what must sometimes have seemed like artistic whims of the author. Thanks also to Paula Falk for help in assembling the figures and to Elaine Lowe, who helped with the proofreading of the manuscript. Finally, I would like to thank William Day, Senior Medical Editor at Springer-Verlag from the time I began this project through the time that I submitted the manuscript. His confidence in the concept of the book helped to motivate me during those times when progress was slow. xi

10 Contents Part I The Ground plan of the Nervous System Ground Plan of the Nervous System I Principles of Central Nervous System Development Ground Plan of the Nervous System II Levels of the Neuraxis Central Nervous System Vasculature, Blood-Brain Barrier, and Cerebrospinal Fluid Part 2 Cellular Basis of Neuronal Signaling Cell Biology of Neurons Cell Biology of Glia Presynaptic Mechanisms Underlying Neurotransmitter Synthesis, Storage, Release and Inactivation Postsynaptic Mechanisms: Neurotransmitter Receptors and Signal Transduction Cascades Neuronal Integration xiii

11 xiv CONTENTS Part] The Somatosensory System Somatic Sensation I Peripheral Receptors and Primary Afferent Neurons Somatic Sensation II Ascending Pathways From the Spinal Cord and Brainstem to the Thalamus Somatic Sensation III The Physiology of Somatic Sensation Somatic Sensation IV Pain Part 4 The Motor System Motor System I The Anatomical Organization of the Motor System Motor System II Segmental Control of Movement: The Motor Unit and Segmental Reflexes Motor System III Supraspinal Control of Movement The Basal Ganglia Role ofthe Cerebellum in Motor Function PartS The Visual System Visual System I The Retina Visual System II Central Pathways That Mediate Visual Perception Visual System III Visual Neurophysiology and Visual Perception Visual System IV Visual Afferent Pathways That Control Eye Movement and Ocular Reflexes Part 6 The Auditory System Auditory System I The Ear and the Auditory Receptive Apparatus in the Cochlea Auditory System II Central Auditory Pathways Auditory System III Auditory Neurophysiology and Auditory Perception

12 CONTENTS XV Part 7 The Vestibular System The Vestibular System Part 8 The Chemical Senses The Chemical Senses Part 9 The Autonomic Nervous System The Autonomic Nervous System Part 10 The Hypothalamus and Limbic System: Substrates of Motivation, Emotion, and Memory The Hypothalamus Coordination of Visceral Operation and the Behaviors That Maintain Bodily Homeostasis The Limbic System Circuits that Underlie Affect and Memory Part 11 Arousal, Attention, Consciousness Modulatory Systems of the Brainstem Higher Cortical Functions, Localization of Function, and Regulation of Consciousness Index