(BQ) Part 1 book “Clinical neuroanatomy” has contents: Introduction and organization of the nervous system; the neurobiology of the neuron and the neuroglia; nerve fibers, peripheral nerves, receptor and effector endings, dermatomes, and muscle activity, the brainstem,… and other contents.
Authors: Snell, Richard S Title: Clinical Neuroanatomy, 7th Edition Copyright ©2010 Lippincott Williams & Wilkins 2010 Lippincott Williams & Wilkins Philadelphia 351 West Camden Street, Baltimore, M D 21201, 530 Walnut Street, Philadelphia, PA 19106 978-0-7817-9427-5 Seventh Edition Copyright © 2010, 2006, 2001, 1997, 1992, 1987, 1980 Lippincott Williams & Wilkins, a Wolters Kluwer business 351 West Camden Street, Baltimore, M D 21201 530 Walnut Street, Philadelphia, PA 19106 Printed in China All rights reserved This book is protected by copyright No part of this book may be reproduced or transmitted in any form or by any means, including as photocopies or scanned-in or other electronic copies, or utilized by any information storage and retrieval system without written permission from the copyright owner, except for brief quotations embodied in critical articles and reviews M aterials appearing in this book prepared by individuals as part of their official duties as U.S government employees are not covered by the abovementioned copyright To request permission, please contact Lippincott Williams & Wilkins at 530 Walnut Street, Philadelphia, PA 19106, via email at permissions@lww.com, or via website at lww.com (products and services) 987654321 Acquisitions Editor: Crystal Taylor Managing Editor: Kelly Horvath Marketing Manager: Emilie Linkins Managing Editor, Production: Eve Malakoff-Klein Designer: Stephen Druding Compositor: Aptara Library of Congress Cataloging-in-Publication Data Snell, Richard S Clinical neuroanatomy / Richard S Snell — 7th ed p ; cm Includes bibliographical references and index ISBN 978-0-7817-9427-5 Neuroanatomy I Title [DNLM : Nervous System—anatomy & histology WL 101 S671c 2010] QM 451.S64 2010 616.8—dc22 2008040897 DISCLAIM ER Care has been taken to confirm the accuracy of the information present and to describe generally accepted practices However, the authors, editors, and publisher are not responsible for errors or omissions or for any consequences from application of the information in this book and make no warranty, expressed or implied, with respect to the currency, completeness, or accuracy of the contents of the publication Application of this information in a particular situation remains the professional responsibility of the practitioner; the clinical treatments described and recommended may not be considered absolute and universal recommendations The authors, editors, and publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accordance with the current recommendations and practice at the time of publication However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any change in indications and dosage and for added warnings and precautions This is particularly important when the recommended agent is a new or infrequently employed drug Some drugs and medical devices presented in this publication have Food and Drug Administration (FDA) clearance for limited use in restricted research settings It is the responsibility of the health care provider to ascertain the FDA status of each drug or device planned for use in their clinical practice To purchase additional copies of this book, call our customer service department at (800) 638-3030 or fax orders to (301) 223-2320 International customers should call (301) 223-2300 Visit Lippincott Williams & Wilkins on the Internet: http://www.lww.com Lippincott Williams & Wilkins customer service representatives are available from 8:30 am to 6:00 pm, EST Authors: Snell, Richard S Title: Clinical Neuroanatomy, 7th Edition Copyright ©2010 Lippincott Williams & Wilkins > Fr ont of Book > Author s Author Richard S Snell M.R.C.S., L.R.C.P., MB, BS, MD, PhD Emeritus Professor of Anatomy George Washington University, School of Medicine and Health Sciences, Washington, DC; Formerly Associate Professor of Anatomy and Medicine, Yale University Medical School; Lecturer in Anatomy King's College University of London; and Visiting Professor of Anatomy, Harvard Medical School Authors: Snell, Richard S Title: Clinical Neuroanatomy, 7th Edition Copyright ©2010 Lippincott Williams & Wilkins > Fr ont of Book > Pr eface Preface This book contains the basic neuroanatomical facts necessary for the practice of medicine It is suitable for medical students, dental students, nurses, and allied health students Residents fnd this book useful during their rotations The functional organization of the nervous system has been emphasized and indicates how injury and disease can result in neurologic deficits The amount of factual information has been strictly limited to that which is clinically important In this edition, the content of each chapter has been reviewed, obsolete material has been discarded, and new material added Each chapter is divided into the following categories: Clinical Example A short case report that serves to dramatize the relevance of neuroanatomy introduces each chapter Chapter Objectives This section details the material that is most important to learn and understand in each chapter Basic Neuroanatomy This section provides basic information on neuroanatomical structures that are of clinical importance Numerous examples of normal radiographs, CT scans, M RIs, and PET scans are also provided M any cross-sectional diagrams have been included to stimulate students to think in terms of three-dimensional anatomy, which is so important in the interpretation of CT scans and M RI images Clinical Notes This section provides the practical application of neuroanatomical facts that are essential in clinical practice It emphasizes the structures that the physician will encounter when making a diagnosis and treating a patient It also provides the information necessary to understand many procedures and techniques and notes the anatomical “pitfalls” commonly encountered Clinical Problem Solving This section provides the student with many examples of clinical situations in which a knowledge of neuroanatomy is necessary to solve clinical problems and to institute treatment; solutions to the problems are provided at the end of the chapter Review Questions The purpose of the questions is threefold: to focus attention on areas of importance, to enable students to assess their areas of weakness, and to provide a form of self-evaluation when questions are answered under examination conditions Some of the questions are centered around a clinical problem that requires a neuroanatomical answer Solutions to the problem are provided at the end of each chapter In addition to the full text from the book, an interactive Review Test, including over 450 questions, is provided online The book is extensively illustrated The majority of the figures have been kept simple and are in color As in the previous edition, a concise Color Atlas of the dissected brain is included prior to the text This small but important group of colored plates enables the reader to quickly relate a particular part of the brain to the whole organ References to neuroanatomical literature are included should readers wish to acquire a deeper knowledge of an area of interest R S S Authors: Snell, Richard S Title: Clinical Neuroanatomy, 7th Edition Copyright ©2010 Lippincott Williams & Wilkins > Fr ont of Book > Acknow ledgments Acknowledgments Iam greatly indebted to the following colleagues who provided me with photographic examples of neuroanatomical material: Dr N Cauna, Emeritus Professor of Anatomy, University of Pittsburgh School of M edicine; Dr F M J Fitzgerald, Professor of Anatomy, University College, Galway, Ireland; and Dr A Peters, Professor of Anatomy, Boston University School of M edicine M y special thanks are owed to Larry Clerk, who, as a senior technician in the Department of Anatomy at the George Washington University School of M edicine and Health Sciences, greatly assisted me in the preparation of neuroanatomical specimens for photography I am also grateful to members of the Department of Radiology for the loan of radiographs and CT scans that have been reproduced in different sections of this book I am most grateful to Dr G Size of the Department of Radiology at Yale University M edical Center for examples of CT scans and M RI images of the brain I also thank Dr H Dey, Director of the PET Scan Unit of the Department of Radiology, Veterans Affairs M edical Center, West Haven, Connecticut, for several examples of PET scans of the brain I thank the medical photographers of the Department of Radiology at Yale for their excellent work in reproducing the radiographs As in the past, I express my sincere thanks to M yra Feldman and Ira Grunther, AM I, for the preparation of the very fine artwork Finally, to the staff of Lippincott Williams & Wilkins, I again express my great appreciation for their continued enthusiasm and support throughout the preparation of this book Authors: Snell, Richard S Title: Clinical Neuroanatomy, 7th Edition Copyright ©2010 Lippincott Williams & Wilkins > Fr ont of Book > Color Atlas of Br ain Color Atlas of Brain Figure CA-1 Top: Superior view of the brain Bottom: Inferior view of the brain Figure CA-2 Top: Anterior view of the brain Bottom: Posterior view of the brain Figure CA-3 Top: Right lateral view of the brain Bottom: M edial view of the right side of the brain following median sagitttal section (a) Premotor area (b) Primary somesthetic area (c) Primary visual area (d) Primary motor area (e) None of the above View Answer Figure 8-10 M edial view of the left cerebral hemisphere The answers for Figure 8-10, which shows the medial view of the left cerebral hemisphere, are as follows: Directions: Each case history is followed by questions Read the case history, then select the ONE BEST lettered answer A 54-year-old woman was seen by a neurologist because her sister had noticed a sudden change in her behavior On questioning, the patient stated that after waking up from a deep sleep about a week ago, she noticed that the left side of her body did not feel as if it belonged to her Later, the feeling worsened, and she became unaware of the existence of her left side Her sister told the neurologist that the patient now neglects to wash the left side of her body 17 The neurologist examined the patient and found the following most likely signs except: (a) It was noted that the patient did not look toward her left side (b) She readily reacted to sensory stimulation of her skin on the left side (c) On being asked to move her left leg, she promptly did so (d) There was definite evidence of muscular weakness of the upper and lower limbs on the left side (e) On being asked to walk across the examining room, she tended not to use her left leg as much as her right leg View Answer 18 The neurologist made the following likely conclusions except: (a) The diagnosis of left hemiasomatognosia (loss of appreciation of the left side of the body) was made (b) This condition probably resulted from a lesion of the left parietal lobe (c) In addition, the patient exhibited left hemiakinesia (unilateral motor neglect) (d) There was probably a lesion in areas and of the medial and lateral premotor regions of the right frontal lobe (e) The failure to look toward the left side (visual extinction) suggested a lesion existed in the right parietooccipital lobes View Answer Additional Reading Adams, J H., and Duchen, L W Greenfield's Neuropathology New York: Oxford University Press, 1992 Bates, D The management of medical coma J Neurol Neurosurg Psychiatry 56:589, 1993 Benson, D F The Neurology of Thinking New York: Oxford University Press, 1994 Bloodstein, O Speech Pathology: An Introduction Boston: Houghton M ifflin, 1979 Brodmann, K Vergleichende Lokalisationslebre der Grossbirnrinde Leipzig: Barth, 1909 Bunch, M Dynamics of the Singing Voice Vienna: Springer, 1997 Campbell, A W Histological Studies on the Localization of Cerebral Function Cambridge, M A: Harvard University Press, 1905 Cowan, N Attention and Memory: An Integrated Framework New York: Oxford University Press, 1995 De Gelder, B., and M orais, J Speech and Reading Hillsdale, NJ: Lawrence Erlbaum Associates, 1995 Easton, J D Coma and related disorders In J H Stein (ed.), Internal Medicine (4th ed.) St Louis: M osby, 1993 Goetz, C G Textbook of Clinical Neurology (2nd ed.) Philadelphia: Saunders, 2003 Guyton, A C., and Hall, J E Textbook of Medical Physiology (11th ed.) Philadelphia: Elsevier Saunders, 2006 Iaccino, J F Left Brain–Right Brain Differences: Inquiries, Evidence, and New Approaches Hillsdale, NJ: Lawrence Erlbaum Associates, 1993 Jackson, J H Selected writings of John Hughlings Jackson In J Taylor (ed.), On Epilepsy and Epileptiform Convulsions (vol 1) London: Hodder & Stoughton, 1931 Jasper, H H., Ward, A A., and Pope, A (eds.) Basic Mechanisms of the Epilepsies Boston: Little, Brown, 1969 Kandel, E R., Schwartz, J H., and Jessell, T M Principles of Neural Science (4th ed.) New York: M cGraw-Hill, 2000 Kapur, N Memory Disorders in Clinical Practice Hillsdale, NJ: Lawrence Erlbaum Associates, 1994 Levin, H S., Eisenberg, H M , and Benton, A L Frontal Lobe Function and Dysfunction New York: Oxford University Press, 1991 M ori, H Molecular Biology of Alzheimer's Disease and Animal Models New York: Elsevier, 1998 Penfield, W., and Boldrey, E Somatic motor and sensory representation in the cerebral cortex of man as studied by electrical stimulation Brain 60:389, 1937 Penfield, W., and Rasmussen, T The Cerebral Cortex of Man: A Clinical Study of Localization of Function New York: M acmillan, 1950 Penfield, W., and Roberts, L Speech and Brain Mechanisms Princeton, NJ: Princeton University Press, 1959 Porter, R The cerebral cortex and control of movement performance In M Swash and C Kennard (eds.), Scientific Basis of Clinical Neurology (p 19) Edinburgh: Churchill Livingstone, 1985 Rhoades, R A., and Tanner, G A Medical Physiology Boston: Little, Brown, 1995 Seeman, P., Gaun, H C., and Van Tol, H H M Dopamine D4 receptors elevated in schizophrenia Nature 365:441–445, 1993 Sholl, D A Organization of the Cerebral Cortex London: M ethuen, 1956 Snell, R S., and Smith, M S Clinical Anatomy for Emergency Medicine St Louis: M osby, 1993 Sperry, R W Lateral specialization in the surgically separated hemispheres In The Neurosciences, Third Study Program (p 5) Cambridge, M A: M IT Press, 1974 Springer, S P Left Brain, Right Brain: Perspectives from Cognitive Neuroscience New York: Freeman, 1998 Standring, S (ed) Gray's Anatomy (39th Br ed.) London: Elsevier Churchill Livingstone, 2005 Authors: Snell, Richard S Title: Clinical Neuroanatomy, 7th Edition Copyright ©2010 Lippincott Williams & Wilkins > Table of Contents > Chapter - The Reticular For mation and the Limbic System Chapter The Reticular Formation and the Limbic System A 24-year-old medical student was rushed by ambulance to the emergency department after an accident on his motorcycle On examination, he was found to be unconscious and showed evidence of severe injury to the right side of his head He failed to respond to the spoken word, and he did not make any response to deep painful pressure applied over his supraorbital nerve The plantar reflexes were extensor, and the corneal, tendon, and pupillary reflexes were absent It was clear that the patient was in a deep coma Further neurologic examination revealed nothing that might add to the diagnosis A computed tomography scan showed a large depressed fracture of the right parietal bone of the skull After a week in the intensive care unit, the patient's condition changed He suddenly showed signs of being awake but not aware of his environment or inner needs To the delight of his family, he followed them with his eyes and responded in a limited manner to primitive postural and reflex movements; he did not, however, speak and did not respond to commands Although he had sleep-awake cycles, he did not respond appropriately to pain The patient's neurologic condition was unchanged months later The neurologist determined that the patient was awake but not aware of his surroundings He explained to the relatives that the part of the brain referred to as the reticular formation in the brainstem had survived the accident and was responsible for the patient apparently being awake and able to breathe without assistance However, the tragedy was that his cerebral cortex was dead, and the patient would remain in this vegetative state Chapter Objectives To provide a brief overview of the structure and function of the reticular formation and present, in the simplest terms, the parts of the limbic system and its functions Not very long ago, the reticular system was believed to be a vague network of nerve cells and fibers occupying the central core of the brainstem with no particular function Today, it is known to play a key role in many important activities of the nervous system Limbic system was a term loosely used to describe the part of the brain between the cerebral cortex and the hypothalamus, a little understood area of the brain Today, it is known to play a vital role in emotion, behavior, drive, and memory Reticular Formation The reticular formation, as its name would suggest, resembles a net (reticular) that is made up of nerve cells and nerve fibers The net extends up through the axis of the central nervous system from the spinal cord to the cerebrum It is strategically placed among the important nerve tracts and nuclei It receives input from most of the sensory systems and has efferent fibers that descend and influence nerve cells at all levels of the central nervous system The exceptionally long dendrites of the neurons of the reticular formation permit input from widely placed ascending and descending pathways Through its many connections, it can influence skeletal muscle activity, somatic and visceral sensations, the autonomic and endocrine systems, and even the level of consciousness General Arrangement The reticular formation consists of a deeply placed continuous network of nerve cells and fibers that extend from the spinal cord through the medulla, the pons, the midbrain, the subthalamus, the hypothalamus, and the thalamus The diffuse network may be divided into three longitudinal columns: the first occupying the median plane, called the median column, and consisting of intermediate-size neurons; the second, called the medial column, containing large neurons; and the third, or lateral column, containing mainly small neurons (Fig 9-1) With the classic neuronal staining techniques, the groups of neurons are poorly defined, and it is difficult to trace an anatomical pathway through the network However, with the new techniques of neurochemistry and cytochemical localization, the reticular formation is shown to contain highly organized groups of transmitter-specific cells that can influence functions in specific areas of the central nervous system The monoaminergic groups of cells, for example, are located in well-defined areas throughout the reticular formation Polysynaptic pathways exist, and both crossed and uncrossed ascending and descending pathways are present, involving many neurons that serve both somatic and visceral functions Inferiorly, the reticular formation is continuous with the interneurons of the gray matter of the spinal cord, while superiorly, impulses are relayed to the cerebral cortex; a substantial projection of fibers also leaves the reticular formation to enter the cerebellum Afferent Projections M any different afferent pathways project onto the reticular formation from most parts of the central nervous system (Fig 9-2) From the spinal cord, there are the spinoreticular tracts, the spinothalamic tracts, and the medial lemniscus From the cranial nerve nuclei, there are ascending afferent tracts, which include the vestibular, acoustic, and visual pathways From the cerebellum, there is the cerebelloreticular pathway From the subthalamic, hypothalamic, and thalamic nuclei and from the corpus striatum and the limbic system, there are further afferent tracts Other important afferent fibers arise in the primary motor cortex of the frontal lobe and from the somesthetic cortex of the parietal lobe Efferent Projections M ultiple efferent pathways extend down to the brainstem and spinal cord through the reticulobulbar and reticulospinal tracts to neurons in the motor nuclei of the cranial nerves and the anterior horn cells of the spinal cord Other descending pathways extend to the sympathetic outflow and the craniosacral parasympathetic outflow of the autonomic nervous system Additional pathways extend to the corpus striatum, the cerebellum, the red nucleus, the substantia nigra, the tectum, and the nuclei of the thalamus, subthalamus, and hypothalamus M ost regions of the cerebral cortex receive efferent fibers as well Functions of the Reticular Formation From the previous description of the vast number of connections of the reticular formation to all parts of the nervous system, it is not surprising to find that the functions are many A few of the more important functions are considered here Control of skeletal muscle Through the reticulospinal and reticulobulbar tracts, the reticular formation can influence the activity of the alpha and gamma motor neurons Thus, the reticular formation can modulate muscle tone and P.307 reflex activity It can also bring about reciprocal inhibition; for example, when the flexor muscles contract, the antagonistic extensors relax The reticular formation, assisted by the vestibular apparatus of the inner ear and the vestibular spinal tract, plays an important role in maintaining the tone of the antigravity muscles when standing The so-called respiratory centers of the brainstem, described by neurophysiologists as being in the control of the respiratory muscles, are now considered part of the reticular formation Figure 9-1 Diagram showing the approximate positions of the median, medial, and lateral columns of the reticular formation in the brainstem Figure 9-2 Diagram showing the afferent fibers of the reticular formation The reticular formation is important in controlling the muscles of facial expression when associated with emotion For example, when a person smiles or laughs in response to a joke, the motor control is provided by the reticular formation on both sides of the brain The descending tracts are separate from the corticobulbar fibers This means that a person who has suffered a stroke that involves the corticobulbar fibers and exhibits facial paralysis on the lower part of the face is still able to smile symmetrically (see p 361) Control of somatic and visceral sensations By virtue of its central location in the cerebrospinal axis, the reticular formation can influence all ascending pathways that pass to supraspinal levels The influence may be facilitative or inhibitory In particular, the reticular formation may have a key role in the “gating mechanism” for the control of pain perception (see p 147) Control of the autonomic nervous system Higher control of the autonomic nervous system, from the cerebral cortex, hypothalamus, and other subcortical nuclei, can be exerted by the reticulobulbar and reticulospinal tracts, which descend to the sympathetic outflow and the parasympathetic craniosacral outflow Control of the endocrine nervous system Either directly or indirectly through the hypothalamic nuclei, the reticular formation can influence the synthesis or release of releasing or release-inhibiting factors and thereby control the activity of the hypophysis cerebri Influence on the biologic clocks By means of its multiple afferent and efferent pathways to the hypothalamus, the reticular formation probably influences the biologic rhythms The reticular activating system Arousal and the level of consciousness are controlled by the reticular formation M ultiple ascending pathways carrying sensory information to higher centers are channeled through the reticular formation, which, in turn, projects this information to different parts of the cerebral cortex, causing a sleeping person to awaken In fact, it is now believed that the state of consciousness is dependent on the continuous projection of sensory information to the cortex Different degrees of wakefulness seem to depend on the degree of activity of the reticular formation Incoming pain sensations strongly increase the activity of the reticular formation, which, in turn, greatly excites the cerebral cortex Acetylcholine plays a key role as an excitatory neurotransmitter in this process From the above description, it must be apparent that the reticular formation, almost totally ignored in the past, is now being shown to influence practically all activities of the body Limbic System The word limbic means border or margin, and the term limbic system was loosely used to include a group of structures that lie in the border zone between the cerebral cortex and the hypothalamus Now it is recognized, as the result of research, that the limbic system is involved with many other structures beyond the border zone in the control of emotion, behavior, and drive; it also appears to be important to memory Anatomically, the limbic structures include the subcallosal, the cingulate, and the parahippocampal gyri, the hippocampal formation, the amygdaloid nucleus, the mammillary bodies, and the anterior thalamic nucleus (Fig 9-3) The alveus, the fimbria, the fornix, the mammillothalamic tract, and the stria terminalis constitute the connecting pathways of this system Hippocampal Formation The hippocampal formation consists of the hippocampus, the dentate gyrus, and the parahippocampal gyrus The hippocampus is a curved elevation of gray matter that extends throughout the entire length of the floor of the inferior horn of the lateral ventricle (Fig 9-4) Its anterior end is expanded to form the pes hippocampus It is named hippocampus because it resembles a sea horse in coronal section The convex ventricular surface is covered with ependyma, beneath which lies a thin layer of white matter called the alveus (Fig 9-5) The alveus consists of nerve fibers that have originated in the hippocampus, and these converge medially to form a bundle called the fimbria (Figs 9-4 and 9-5) The fimbria, in turn, becomes continuous with the crus of the fornix (Fig 9-4) The hippocampus terminates posteriorly beneath the splenium of the corpus callosum The dentate gyrus is a narrow, notched band of gray matter that lies between the fimbria of the hippocampus and the parahippocampal gyrus (Fig 9-4) Posteriorly, the gyrus accompanies the fimbria almost to the splenium of the corpus callosum and becomes continuous with the indusium griseum The indusium griseum is a thin, vestigial layer of gray matter that covers the superior surface of the corpus callosum (Fig 9-6) Embedded in the superior surface of the indusium griseum are two slender bundles of white fibers on each side called the medial and lateral longitudinal striae The striae are the remains of the white matter of the vestigial indusium griseum Anteriorly, the dentate gyrus is continued into the uncus The parahippocampal gyrus lies between the hippocampal fissure and the collateral sulcus and is continuous with the hippocampus along the medial edge of the temporal lobe (Figs 9-4 and 9-5) Figure 9-3 M edial aspect of the right cerebral hemisphere showing structures that form the limbic system Figure 9-4 Dissection of the right cerebral hemisphere exposing the cavity of the lateral ventricle, showing the hippocampus, the dentate gyrus, and the fornix Figure 9-5 Coronal section of the hippocampus and related structures Figure 9-6 Dissection of both cerebral hemispheres showing the superior surface of the corpus callosum Amygdaloid Nucleus The amygdaloid nucleus is so named because it resembles an almond It is situated partly anterior and partly superior to the tip of the inferior horn of the lateral ventricle (see Fig 7-15) It is fused with the tip of the tail of the caudate nucleus, which has passed anteriorly in the roof of the inferior horn of the lateral ventricle The stria terminalis emerges from its posterior aspect The amygdaloid nucleus consists of a complex of nuclei that can be grouped into a larger basolateral group and smaller corticomedial group The mammillary bodies and the anterior nucleus of the thalamus are considered elsewhere in this text Connecting Pathways of the Limbic System The connecting pathways of the limbic system are the alveus, the fimbria, the fornix, the mammillothalamic tract, and the stria terminalis The alveus consists of a thin layer of white matter that lies on the superior or ventricular surface of the hippocampus (Fig 9-5) It is composed of nerve fibers that originate in the hippocampal cortex The fibers converge on the medial border of the hippocampus to form a bundle called the fimbria The fimbria now leaves the posterior end of the hippocampus as the crus of the fornix (Fig 9-4) The crus from each side curves posteriorly and superiorly beneath the splenium of the corpus callosum and around the posterior surface of the thalamus The two crura now converge to form the body of the fornix, which is applied closely to the undersurface of the corpus callosum (Fig 9-3) As the two crura come together, they are connected by transverse fibers called the commissure of the fornix (see Fig 7-17) These fibers decussate and join the hippocampi of the two sides Anteriorly, the body of the fornix is connected to the undersurface of the corpus callosum by the septum pellucidum Inferiorly, the body of the fornix is related to the tela choroidea and the ependymal roof of the third ventricle The body of the fornix splits anteriorly into two anterior columns of the fornix, each of which curves anteriorly and inferiorly over the interventricular foramen (foramen of M onro) Then, each column disappears into the lateral wall of the third ventricle to reach the mammillary body (Fig 9-3) The mammillothalamic tract provides important connections between the mammillary body and the anterior nuclear group of the thalamus The stria terminalis emerges from the posterior aspect of the amygdaloid nucleus and runs as a bundle of nerve fibers posteriorly in the roof of the inferior horn of the lateral ventricle on the medial side of the tail of the caudate nucleus (Fig 9-3) It follows the curve of the caudate nucleus and comes to lie in the floor of the body of the lateral ventricle Structure of the Hippocampus and the Dentate Gyrus The cortical structure of the parahippocampal gyrus is six layered (Fig 9-5) As the cortex is traced into the hippocampus, there is a gradual transition from a six- to a three-layered arrangement These three layers are the superficial molecular layer, consisting of nerve fibers and scattered small neurons; the pyramidal layer, consisting of many large pyramid-shaped neurons; and the inner polymorphic layer, which is similar in structure to the polymorphic layer of the cortex seen elsewhere The dentate gyrus also has three layers, but the pyramidal layer is replaced by the granular layer (Fig 9-5) The granular layer is composed of densely arranged rounded or oval neurons that give rise to axons that terminate on the dendrites of the pyramidal cells in the hippocampus A few of the axons join the fimbria and enter the fornix Afferent Connections of the Hippocampus Afferent connections of the hippocampus may be divided into six groups (Fig 9-7): Fibers arising in the cingulate gyrus pass to the hippocampus Fibers arising from the septal nuclei (nuclei lying within the midline close to the anterior commissure) pass posterior in the fornix to the hippocampus Fibers arising from one hippocampus pass across the midline to the opposite hippocampus in the commissure of the fornix Fibers from the indusium griseum pass posteriorly in the longitudinal striae to the hippocampus Fibers from the entorhinal area or olfactory-associated cortex pass to the hippocampus Fibers arising from the dentate and parahippocampal gyri travel to the hippocampus Efferent Connections of the Hippocampus Axons of the large pyramidal cells of the hippocampus emerge to form the alveus and the fimbria The fimbria continues as the crus of the fornix The two crura converge to form the body of the fornix The body of the fornix splits into the two columns of the fornix, which curve downward and forward in front of the interventricular foramina The fibers within the fornix are distributed to the following regions (Fig 9-7): Fibers pass posterior to the anterior commissure to enter the mammillary body, where they end in the medial nucleus Fibers pass posterior to the anterior commissure to end in the anterior nuclei of the thalamus Fibers pass posterior to the anterior commissure to enter the tegmentum of the midbrain Fibers pass anterior to the anterior commissure to end in the septal nuclei, the lateral preoptic area, and the anterior part of the hypothalamus Fibers join the stria medullaris thalami to reach the habenular nuclei Consideration of the above complex anatomical pathways indicates that the structures comprising the limbic system not only are interconnected but also send projection fibers to many different parts of the nervous system Physiologists now recognize the importance of the hypothalamus as being the major output pathway of the limbic system Figure 9-7 Diagram showing some important afferent and efferent connections of the limbic system Functions of the Limbic System The limbic system, via the hypothalamus and its connections with the outflow of the autonomic nervous system and its control of the endocrine system, is able to influence many aspects of emotional behavior These include particularly the reactions of fear and anger and the emotions associated with sexual behavior There is also evidence that the hippocampus is concerned with converting recent memory to long-term memory A lesion of the hippocampus results in the individual being unable to store long-term memory M emory of remote past events before the lesion developed is unaffected This condition is called anterograde amnesia It is interesting to note that injury to the amygdaloid nucleus and the hippocampus produces a greater memory loss than injury to either one of these structures alone There is no evidence that the limbic system has an olfactory function The various afferent and efferent connections of the limbic system provide pathways for the integration and effective homeostatic responses to a wide variety of environmental stimuli Clinical Notes Reticular Formation The reticular formation is a continuous network of nerve cells and fibers that extend through the neuroaxis from the spinal cord to the cerebral cortex The reticular formation not only modulates the control of motor systems but also influences sensory systems By means of its multiple ascending pathways, which project to different parts of the cerebral cortex, it is believed to influence the state of consciousness Loss of Consciousness In experimental animals, damage to the reticular formation, which spares the ascending sensory pathways, causes persistent unconsciousness Pathologic lesions of the reticular formation in humans can result in loss of consciousness and even coma It has been suggested that the loss of consciousness that occurs in epilepsy may be due to inhibition of the activity of the reticular formation in the upper part of the diencephalon Limbic System The anatomical connections of the limbic system are extremely complex, and since their significance is not fully understood, it is unnecessary for a student of medicine to commit all of them to memory The results of neurophysiologic experiments, which have included stimulation and ablation of different parts of the limbic system in animals, are not entirely clear Nevertheless, certain important roles have been inferred: (1) The limbic structures are involved in the development of sensations of emotion and with the visceral responses accompanying those emotions, and (2) the hippocampus is concerned with recent memory Schizophrenia The symptoms of schizophrenia include chronically disordered thinking, blunted affect, and emotional withdrawal Paranoid delusions and auditory hallucinations may also be present Clinical research has shown that if the limbic receptors to dopamine are blocked by a pharmacologic agent, the worst symptoms of schizophrenia are lessened Phenothiazine administration, for example, blocks the dopamine receptors in the limbic system Unfortunately, this drug, as well as most other antipsychotic drugs, has major motor side effects on the dopaminergic receptors within the extrapyramidal system, producing abnormal involuntary movements Research is now concentrating on finding a drug that will block the limbic dopamine receptors but without effect on the receptors of the extrapyramidal system (substantia nigra–corpus striatum) It is clear, however, that there is still no direct evidence that excessive production of dopamine by certain neurons actually contributes to schizophrenia Destruction of the Amygdaloid Complex Unilateral or bilateral destruction of the amygdaloid nucleus and the para-amygdaloid area in patients suffering from aggressive behavior in many cases results in a decrease in aggressiveness, emotional instability, and restlessness; increased interest in food; and hypersexuality There is no disturbance in memory Monkeys that have been subjected to bilateral removal of the temporal lobes demonstrate what is known as the Klüver-Bucy syndrome They become docile and show no evidence of fear or anger and are unable to appreciate objects visually They have an increased appetite and increased sexual activity Moreover, the animals indiscriminately seek partnerships with male and female animals Precise stereotactic lesions in the amygdaloid complex in humans reduce emotional excitability and bring about normalization of behavior in patients with severe disturbances No loss of memory occurs Temporal Lobe Dysfunction Temporal lobe epilepsy may be preceded by an aura of acoustic or olfactory experience The olfactory aura is usually an unpleasant odor The patient is often confused, anxious, and docile and may perform automatic and complicated movements, such as undressing in public or driving a car, and then, following the seizure, may have no memory of what occurred previously Clinical Problem Solving While discussing the neurologic basis of emotions during a ward round, a neurologist asked a third-year medical student what she knew about the Klüver-Bucy syndrome What would be your answer to that question? Does KlüverBucy syndrome ever occur in humans? View Answer A 23-year-old woman with a 4-year history of epileptic attacks visited her neurologist A friend of hers vividly described one of her attacks For a few seconds before the convulsions began, the patient would complain of an unpleasant odor, similar to that encountered in a cow shed This was followed by a shrill cry as she fell to the floor unconscious Her whole body immediately became involved in generalized tonic and clonic movements Clearly, this patient had a generalized form of epileptic seizure Using your knowledge of neuroanatomy, suggest which lobe of the brain was initially involved in the epileptic discharge View Answer A 54-year-old man died in the hospital with a cerebral tumor He had always been intellectually very bright and could easily recall events in his childhood For the past months, his family had noticed that he had difficulty in recalling where he had placed things, such as his pipe He also had difficulty in recalling recent news events, and just before he died, he could not remember that his brother had visited him the day before Using your knowledge of neuroanatomy, suggest which part of the brain was being affected by the expanding and highly invasive tumor View Answer P.314 Review Questions Directions: Each of the numbered items in this section is followed by answers Select the ONE lettered answer that is CORRECT The following statements concern the reticular formation: (a) Reticulobulbar and reticulospinal tracts form the afferent pathways from the reticular formation to the motor nuclei of the cranial nerves and the anterior horn cells of the spinal cord, respectively (b) The reticular formation extends through the neuroaxis from the spinal cord to the midbrain (c) The main pathways through the reticular formation may easily be traced from one part of the central nervous system to another using silver stains (d) Superiorly, the reticular formation is relayed to the cerebral cortex (e) Afferent pathways project into the reticular formation from only a few parts of the central nervous system View Answer The following statements concern the functions of the reticular formation: (a) It influences the activity of the alpha and gamma motor neurons (b) It opposes the actions of the vestibular spinal tract (c) It does not bring about reciprocal inhibition during contraction of the prime mover muscles (d) It plays no part in maintaining the tone of the antigravity muscles (e) It cannot modulate reflex activity View Answer The following statements concern the functions of the reticular formation: (a) It does not affect the reception of pain (b) It cannot influence all ascending pathways to the supraspinal levels (c) By means of its reticulobulbar and reticulospinal tracts, it can control the parasympathetic and sympathetic outflows (d) It has no effect on the biologic rhythms (e) It does not influence the degree of wakefulness of an individual View Answer Anatomically, the following structures collectively form the limbic system: (a) The amygdaloid nucleus, the red nucleus, and the vestibular nuclei (b) The pulvinar of the thalamus and the substantia nigra (c) The hippocampal formation (d) The cingulate gyrus and the uncus (e) The subcallosal, the cingulate, and the parahippocampal gyri, the hippocampal formation, the amygdaloid nucleus, the mammillary bodies, and the anterior thalamic nuclei View Answer The following statements concern the efferent connections of the hippocampus: (a) They arise from the small granular cells of the cortex (b) They travel through the fornix (c) None of the fibers enter the mammillary body (d) The fibers within the fornix pass posterior to the interventricular foramen (e) Some of the fibers end in the posterior nuclei of the thalamus View Answer The following statements concern the functions of the limbic system: (a) It is not concerned with the reactions of fear and anger (b) It is concerned with visual experiences (c) The hippocampus is concerned with recent memory (d) The limbic system plays an important role in olfactory function (e) It directly influences the activity of the endocrine system View Answer Figure 9-8 M edial aspect of the right cerebral hemisphere showing structures that form the limbic system The answers for Figure 9-8 are as follows: Matching Questions Directions: The following questions apply to Figure 9-8 Match the numbers listed on the left with the appropriate lettered structure listed on the right Each lettered option may be selected once, more than once, or not at all Number (a) Uncus (b) Body of fornix (c) Parahippocampal gyrus (d) Dentate gyrus (e) None of the above View Answer Number (a) Uncus (b) Body of fornix (c) Parahippocampal gyrus (d) Dentate gyrus (e) None of the above View Answer Number (a) Uncus (b) Body of fornix (c) Parahippocampal gyrus (d) Dentate gyrus (e) None of the above View Answer 10 Number (a) Uncus (b) Body of fornix (c) Parahippocampal gyrus (d) Dentate gyrus (e) None of the above View Answer Additional Reading Aggleton, J P (ed.) The Amygdala: Neurobiological Aspects of Emotion, Memory, and Mental Dysfunction New York: Wiley-Liss, 1993 Goldman-Rakic, P S Working memory and the mind Sci Am 267:110, 1992 Guyton, A C., and Hall, J E Textbook of Medical Physiology (11th ed.) Philadelphia: Elsevier Saunders, 2006 Jasper, H H., Descarries, L., Castelluci, V F., and Rossignol, S (eds.) Consciousness: At the Frontiers of Neuroscience Philadelphia: Lippincott-Raven, 1998 Kiernan, J A The Human Nervous System (7th ed.) Philadelphia: Lippincott Williams & Wilkins, 1998 Klemm, W R Ascending and descending excitatory influences in the brain stem reticulum: A re-examination Brain Res 36:444, 1972 M ega, M S., Cummings, J L., Salloway, S., and M alloy, P The limbic system: An anatomic, phylogenetic, and clinical perspective J Neuropsychiatry Clin Neurosci 9:315, 1997 Rowland, L P Merritt's Textbook of Neurology Baltimore: Williams & Wilkins, 1995 Ryan, P M Epidemiology, etiology, diagnosis and treatment of schizophrenia Am J Hosp Pharm 48:1271, 1991 Seeman, P., Guan, H C., and Van Tol, H H M Dopamine D4 receptors elevated in schizophrenia Nature 365:441–445, 1993 Standring, S (ed.) Gray's Anatomy (39th Br ed.) London: Elsevier Churchill Livingstone, 2005 Steriade, M Arousal: Revisiting the reticular activating system Science 272:225, 1996 ... 19 106 978-0-7 817 -9427-5 Seventh Edition Copyright © 2 010 , 2006, 20 01, 19 97, 19 92, 19 87, 19 80 Lippincott Williams & Wilkins, a Wolters Kluwer business 3 51 West Camden Street, Baltimore, M D 212 01. .. lateral ventricles (Fig 1- 11) The hypothalamus forms the lower part of the lateral wall and floor of the third ventricle (Fig 1- 11) Cerebrum The cerebrum, the largest part of the brain, consists... 978-0-7 817 -9427-5 Neuroanatomy I Title [DNLM : Nervous System—anatomy & histology WL 10 1 S671c 2 010 ] QM 4 51. S64 2 010 616 .8—dc22 2008040897 DISCLAIM ER Care has been taken to confirm the accuracy of