GRAY’S Clinical Neuroanatomy The Anatomic Basis for Clinical Neuroscience

GRAY’S Clinical Neuroanatomy The Anatomic Basis for Clinical NeuroscienceEditor

Elliott L. Mancall, MDEmeritus Professor of NeurologyDepartment of NeurologyThomas Jefferson UniversityJefferson Medical CollegePhiladelphia, Pennsylvania

Associate Editor

David G. Brock, MD, CIPMedical DirectorNeuronetics, Inc.Malvern, Pennsylvania

Excerpts from Gray’s AnatomySusan Standring, Editor-in-ChiefAlan Crossman, Section Editor

Copyright in the cover image is owned by Thomas Jefferson University 2010, all rights reserved.

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GRAY’S CLINICAL NEUROANATOMY: THE ANATOMIC BASIS FOR CLINICAL NEUROSCIENCE ISBN: 978-1-4160-4705-6

Copyright © 2011 by Saunders, an imprint of Elsevier Inc.

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DedicationTo our wives, J.C.M. and C.A.S.—thank you for your support.

Elliott L. MancallDavid G. Brock

Contributors

Michael W. Devereaux, MDProfessor of NeurologyDepartment of NeurologyCase Western Reserve School of Medicine;Staff NeurologistCase Medical CenterCleveland, Ohio

Karl Doghramji, MDProfessor of Psychiatry and Human Behavior, Neurology, and MedicineProgram Director, Fellowship in Sleep MedicineThomas Jefferson University;Medical Director, Jefferson Sleep Disorders CenterThomas Jefferson University HospitalPhiladelphia, Pennsylvania

Keith Dombrowski, MDFellow, Neurocritical CareDepartment of Medicine, Division of NeurologyDuke University Medical CenterDurham, North Carolina

Laurie Gutmann, MDProfessorNeurology and Exercise PhysiologyWest Virginia University School of Medicine;Professor/CNP Fellowship Program DirectorNeurologyRuby Memorial HospitalMorgantown, West Virginia

John Khoury, MDFellow in Sleep MedicineThomas Jefferson University HospitalPhiladelphia, Pennsylvania

Daniel Kremens, MD, JDAssistant Professor of NeurologyThomas Jefferson University HospitalPhiladelphia, Pennsylvania

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Preface

Gray’s Anatomy has been a cornerstone of medical education since its original appear-ance in 1858. It has provided a remarkably authoritative description of both gross and microscopic anatomy of the human body for many generations of medical students and practicing medical scientists on a worldwide basis. It has been, and remains, cher-ished not only as a primary source of anatomical knowledge but also as a reliable resource to which the student or practitioner might return for many years, indeed, throughout the entire length of a medical career. Although the classical text is regularly updated, recent major developments in both basic and clinical medicine have prompted a major reconsideration of the utility of a single large volume devoted to all of human anatomy. Concerns are especially related to the increasing specialization, if not frank fragmentation, of the medical arts with which the contemporary physician must deal on a day-to-day basis. As a consequence of such a reappraisal, a decision has been made to extract focused portions of the major text devoted to specific conceptual domains. Gray’s Anatomy itself will remain as authoritative as ever but will be expanded by the inclusion of clinical case material to illustrate in depth, whenever possible, the application of anatomical principles to the bedside. The field of neuroanatomy lends itself particularly well to such a departure from the more traditional approach to human anatomy, with the original Gray’s material being utilized as the foundation for such an enhanced pedagogical approach. In Gray’s Clinical Neuroanatomy, virtually all the original neuroanatomical text in the thirty-ninth edition is preserved, although it is transposed and rearranged to meet innovative structural guidelines and is comple-mented by a host of clinical case vignettes, which in turn are augmented by visual materials designed to strengthen the link between the clinic and the dissecting room. It must be emphasized that there has been no attempt to develop yet another com-prehensive textbook of neurology as such; the neurological disorders cited here are entirely exemplary and directly relevant to the underlying anatomical principles of the traditional Gray’s.

Organizationally, Gray’s Clinical Neuroanatomy begins with a selection of general, non-systematized topics that lack a specific regional approach—for example, the general vasculature of the brain and spinal cord, the ventricular system and the menin-ges, as well as the general microstructure of the nervous system. A detailed review of neuroembryology and development is also provided; the extraordinary length here reflects the perceived need for in-depth coverage of these topics, which is not available elsewhere. Following these introductory topics, the remaining sections are devoted to the systematized gross and microscopic anatomy of the central and peripheral nervous systems, considered on a regional and clinically pertinent basis, with direct relevance to the bedside and the clinic and thus with direct applicability to the clinician treating a patient with a neurological disease.

Acknowledgments

Dr. David Brock accepted the role of Associate Editor without hesitation and has played a major role not only in refining the clinical parameters of this new Gray’s but also in resolving a number of technical issues inherent in a departure of this sort. This project would never have developed as it did without the input of the other major clinical contributors, Drs. Michael Devereaux and Laurie Gutmann, who took time away from their busy academic and clinical lives to provide the clinical and supplemental illustra-tive material so vital to this effort. Drs. Keith Dombrowski and Karl Doghramji contrib-uted additional clinical material for inclusion, and Drs. Daniel Kremens and John Khoury reviewed manuscript and provided clinical images for which we are grateful. Finally, I would be remiss if I did not cite those who contributed so successfully to the parent Gray’s Anatomy, the remarkable work from which Gray’s Clinical Neuroanatomy is derived.

Special thanks go to the members of the Elsevier community: Susan Pioli, who in a very real sense was vital to the initiation of this project, and Madelene Hyde, Christine Abshire and Cheryl Abbott, who managed to keep us on track and guided us through the intricacies of the contemporary publishing world. Last, Valerie Cabrera handled the secretarial tasks so essential to a project of this sort.

Elliott L. Mancall, MD

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Overview of the Organization of the Nervous System

The human nervous system is the most complex product of biological evolution. The constantly changing patterns of activity of its billions of interactive units represent the fundamental physical basis of every aspect of human behaviour and experience. Many thousands of scientists and clinicians around the world, whether driven by intellectual curiosity or the quest for better methods of disease prevention and treatment, have studied the nervous system over many years. However, our understanding of complex neural organization and function is still quite rudimentary, as is our ability to deal with its many pathologies. Multidisciplinary research into the nervous system is one of the most active areas of contemporary biology and medicine, and rapid advances across a range of fronts bring the realistic prospect of better prevention and treatment of many neurological disorders in the future.

The functional capabilities of the nervous system are a product of its vast population of intercommunicating nerve cells, or neurones, estimated to number on the order of 1010. Neurones encode information, conduct it, sometimes over considerable distances, and then transmit it to other neurones or to non-neural tissues (muscles or glandular cells). Most neurones consist of a central mass of cytoplasm within a limiting cell membrane (the cell body or soma) from which a number of branched processes, termed neurites, extend (Fig. 1.1). One of these, the axon, is usually much longer than the others and normally conducts information away from the cell body. The other processes are termed dendrites, and these typically conduct information toward the soma. The nerve cell membrane is polarized, the inside of the cell being around 70 mV negative with respect to the outside. Information is coded in the form of patterns of transient depolarizations and repolarizations of this membrane potential, known as nerve impulses or action potentials. These are conducted along the axon, which may have collateral branches that permit information to be distributed simultaneously to several targets (Fig. 1.2). Axons possess specialized endings, or axon terminals, that come into close apposition with the membrane of the target cell at synapses, where information passes from one cell to another. Axon terminals may form synaptic contacts with dendrites (axodendritic), cell bodies (axosomatic), other axons (axoaxonic) or non-neural tissue such as muscle cells (neuromuscular junction). Transmission of information to other cells is brought about when action potentials cause the release of specific neurotransmitter substances stored in synaptic vesicles within the presynaptic nerve terminal. Specialized receptors are located on the postsynaptic target cell membrane. The neurotransmitter binds to these and, depending on the nature of the chemical and the receptor, either elicits an excitatory (depolarizing) or inhibitory (hyperpolarizing) response or modulates intracellular second messenger systems.

The huge complexity of the nervous system reflects the fact that individual neurones may make synaptic contact with hundreds or even thousands of other neurones via profuse axonal and dendritic branching (arborization). This is exemplified by the extensive dendritic field of the cerebellar Purkinje cell, which is traversed by thousands of axons, each of which makes synaptic contact as it passes. At the level of the individual neurone, competing incoming excitatory and inhibitory synaptic potentials are summated in time (temporal summation) and between synapses (spatial summation). If the postsynaptic neurone is depolarized above a certain threshold, it fires action potentials that are conducted along the axon to the next target cells.

The nervous system contains far more supporting cells (neuroglia) than neurones. Glia are responsible for creating and maintaining an appropriate environment in which the neurones can operate efficiently; they are not electrically excitable in the same way as neurones.

The nervous system consists of three basic functional types of neurone: afferent (sensory), efferent (motor) and interneurones. At the simplest level of interpretation, they allow the nervous system to detect changes in the internal and external environments and to respond appropriately. The sensory elements are able to detect a wide range of stimuli and subserve the general senses (touch, pressure, temperature, etc.) and the special senses (vision, hearing, smell, taste, vestibular sensation). Motor neurones send axons from the central nervous system to effector organs, chiefly muscles and glands.

Neurones that are confined to the central nervous system and that possess neither sensory nor motor terminals are called interneurones. They greatly outnumber sensory and motor neurones and confer on the nervous system its prodigious capacity to analyse, integrate and store information.

The nervous system is customarily divided into two major parts: the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS consists of the brain and spinal cord. The PNS is composed of cranial nerves and spinal nerves together with their ramifications and certain groupings of cell bodies that constitute the peripheral ganglia. Another convention divides the nervous system into somatic and autonomic components. Anatomically, both of these have elements in the CNS and PNS. The autonomic nervous system, which consists of sympathetic and parasympathetic divisions, is made up of neurones concerned primarily with control of the internal environment through innervation of secretory glands and cardiac and smooth muscle. It is considered in detail in Chapter 21. The wall of the gastrointestinal tract contains neurones capable of sustaining local reflex activity independent of the CNS, which are known as the enteric nervous system.

CENTRAL NERVOUS SYSTEMThe brain and spinal cord (Fig. 1.3) contain the great majority of neuronal cell bodies in the nervous system. In many parts of the CNS the cell bodies of neurones are grouped together and are more or less segregated from axons. The generic term for such collections of cell bodies is grey matter. Smaller aggregations of neuronal cell bodies, which usually share a common functional role, are termed nuclei. It follows that neuronal dendrites and synaptic interactions are mostly confined to grey matter. Axons tend to be grouped together to form white matter, so called because axons are often ensheathed in myelin, which confers a paler colouration. Axons that pass between similar sources or destinations within the CNS tend to run together in defined pathways or tracts. These often cross the midline (decussate), which means that half of the body is, in many respects, controlled by and sends information to the opposite side of the brain.

Some groups of neurones in the spinal cord and brain stem that subserve similar functions are organized into longitudinal columns. The neurones in these columns may be concentrated into discrete, discontinuous nuclei in some areas, such as the cranial nerve nuclei of the brain stem, or they may form more or less continuous longitudinal bands, as in much of the spinal cord (Fig. 1.4). Efferent neurones constitute three such columns. The somatic motor column contains motor neurones, the axons of which serve muscles derived from head somites. The two other columns are related to specialized features of head morphology. Of these, the branchial motor column innervates muscles derived from the wall of the embryonic pharynx (branchial muscles), and the visceral motor column supplies preganglionic parasympathetic fibres to glands and visceral smooth muscle. There are four longitudinal cell columns related to sensory functions. The general somatic sensory column essentially deals with information from the head. Special somatic sensory neurones are related to the special senses and receive vestibular and auditory input. General visceral sensory neurones deal with information from widespread and varied visceral sensory endings, and special visceral sensory neurones are related to the special sense of taste.

The brain and spinal cord receive information from, and send it to, the rest of the body through cranial and spinal nerves, respectively. These contain afferent fibres carrying information from sensory receptors and efferent fibres running to effector organs. Through inherent connections of varying complexity between afferent and efferent components of spinal and cranial nerves, the spinal cord and brain stem have the innate capacity to control many aspects of body function and respond to external and internal stimuli by reflex action. Such functions are under the modulatory influence of rich descending connections from the brain. In addition, afferent input to the spinal cord and brain stem is channelled into various ascending pathways, some of which eventually impinge on the cerebral cortex, conferring conscious awareness.

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Section I / General

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Fig. 1.1 Dark-field illuminated micrograph of a CA3 pyramidal cell in a hippocampal slice culture, intracellularly injected with the dye biocytin. Scale bar 50 μm. (Courtesy of R. Anne McKinney, McGill University, and Mathias Abegg, Brain Research Institute, University of Zurich.)

Axon

Fig. 1.2 Structure of a typical neurone.

Axon collateral

Cell body

Dendrite

Axosomatic synapse

Axodentritic synapse

Axon

Axoaxonic synapse

Synaptic terminals Fig. 1.3 Brain and spinal cord with attached spinal nerve roots and dorsal root ganglia, photographed from the dorsal aspect. (Photograph by Kevin Fitzpatrick on behalf of GKT School of Medicine, London.)

Cerebral hemisphere

Cerebellum

C1

T1

L1

S1

Cervical enlargement

Spinal nerve roots

Lumbar enlargement

Chapter 1 / Overview of the Organization of the Nervous System

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Fig. 6.8). Ascending in sequence from the spinal cord, the principal divisions are the rhombencephalon or hindbrain, the mesencephalon or midbrain and the prosencephalon or forebrain.

The rhombencephalon is subdivided into the myelencephalon or medulla oblongata, the metencephalon or pons and the cerebellum. The medulla oblongata, pons and midbrain are collectively referred to as the brain stem, which lies on the basal portions of the occipital and sphenoid bones (clivus). The medulla oblongata is the most caudal part of the brain stem and is continuous with the spinal cord below the level of the foramen magnum. The pons lies rostral to the medulla and is distinguished by a mass of transverse nerve fibres that connect it to the cerebellum. The midbrain is a short segment of brain stem, rostral to the pons. The cerebellum consists of paired hemispheres united by a median vermis; it lies within the posterior cranial fossa, dorsal to the pons, medulla and caudal midbrain, areas with which it has rich fibre connections.

The prosencephalon may be subdivided into the diencephalon and the telencephalon. The diencephalon comprises mostly the thalamus and

To sustain the energy required by constant neuronal activity, the CNS has a high metabolic rate and a rich blood supply. The blood–brain barrier controls the neuronal environment and imposes severe restrictions on the types of substances that can pass from the blood stream into nervous tissue.

Spinal CordThe spinal cord is located within the vertebral column, lying in the upper two-thirds of the vertebral canal (Ch. 8). It is continuous rostrally with the medulla oblongata. For the most part, the spinal cord controls the functions of, and receives afferent input from, the trunk and limbs. Afferent and efferent connections travel in 31 pairs of segmentally arranged spinal nerves. These attach to the cord as dorsal and ventral rootlets that unite to form the spinal nerves proper (Fig. 1.5). The dorsal and ventral roots are functionally distinct. Dorsal roots carry primary afferent nerve fibres from cell bodies located in dorsal root ganglia. Ventral roots carry efferent fibres from cell bodies located in the spinal grey matter.

Internally, the spinal cord is differentiated into a central core of grey matter surrounded by white matter. The grey matter is configured in a characteristic H, or butterfly, shape that has projections known as dorsal and ventral horns (Fig. 1.6). In general, neurones situated in the dorsal horn are primarily concerned with sensory functions, and those in the ventral horn are mostly associated with motor activities. At certain levels of the spinal cord a small lateral horn is also present, marking the location of the cell bodies of preganglionic sympathetic neurones. The central canal, which is a vestigial component of the ventricular system, lies at the centre of the spinal grey matter and runs the length of the cord. The white matter of the spinal cord consists of ascending and descending axons that link spinal cord segments to one another and link the spinal cord to the brain.

BrainThe brain (encephalon) lies within the cranium. It receives information from, and controls the activities of, the trunk and limbs, mainly through rich connections with the spinal cord. It possesses 12 pairs of cranial nerves through which it communicates mostly with structures of the head and neck. The brain is divided into major regions on the basis of ontogenetic growth in individuals and phylogenetic principles (Figs. 1.7–1.9; see also

Fig. 1.4 Arrangement of sensory and motor cell columns in the spinal cord and brain stem. A, Organization of the primitive spinal cord with a dorsal sensory column (blue), a ventral column (red) and segmentally arranged dorsal and ventral nerve roots. B, Arrangement of adult spinal cord serving the thorax, with sensory and somatic motor columns colour-coded in the same way as in A, with an additional intermediate (lateral) visceral motor column (orange). C, Arrangement of multiple longitudinal columns in the brain stem, where the motor column is now subdivided into three parts and the sensory column into four. For further information about the embryological aspects of the early nervous system, consult Chapter 3. See also Fig. 10.1.

Special somatic sensory (vestibulocochlear)General somatic sensory

Special visceral sensory (taste)General visceral sensory

Visceral motorBranchial motor

Somatic motor

A

B

C

Fig. 1.5 Transverse section through the spinal cord illustrating the disposition of grey and white matter and the attachment of dorsal and ventral spinal nerve roots.

Dorsal root of spinal nerve Dorsal root ganglion

Dorsal horn

Ventral root of spinal nerve

Ventral horn

Efferent neurone cell body

Afferent neurone cell body

Grey matter

White matter

Spinal nerve

Lateral horn

Central canal

Fig. 1.6 Transverse section through the human spinal cord at the lumbar level, stained to demonstrate myelinated nerve fibres in the white matter (blue-black). Grey matter remains relatively unstained. (Figure enhanced by B. Crossman.)

Dorsal hornWhite matter

Grey matter Ventral horn