Thumbnail - download.e-bookshelf.de · 2. Nervous system–Diseases. 3. Veterinary neurology. I. Furr, Martin, editor. II. Reed, Stephen M., editor. [DNLM: 1. Central Nervous System

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Equine Neurology

Equine NeurologySEcoNd EditioN

Martin FurrMarion duPont Scott Equine Medical Center

Virginia‐Maryland Regional College of Veterinary Medicine

Leesburg USA

Stephen ReedRood and Riddle Equine Hospital

Lexington USA

This edition first published 2015 copy 2015 by John Wiley amp Sons Inc

First edition 2008 copy Blackwell Publishing Professional

Editorial Offices1606 Golden Aspen Drive Suites 103 and 104 Ames Iowa 50014‐8300 USAThe Atrium Southern Gate Chichester West Sussex PO19 8SQ UK9600 Garsington Road Oxford OX4 2DQ UK

For details of our global editorial offices for customer services and for information about how to apply for permission to reuse the copyright material in this book please see our website at wwwwileycomwiley‐blackwell

Authorization to photocopy items for internal or personal use or the internal or personal use of specific clients is granted by Blackwell Publishing provided that the base fee is paid directly to the Copyright Clearance Center 222 Rosewood Drive Danvers MA 01923 For those organizations that have been granted a photocopy license by CCC a separate system of payments has been arranged The fee codes for users of the Transactional Reporting Service are ISBN‐13 978‐1‐1185‐0147‐42015

Designations used by companies to distinguish their products are often claimed as trademarks All brand names and product names used in this book are trade names service marks trademarks or registered trademarks of their respective owners The publisher is not associated with any product or vendor mentioned in this book

The contents of this work are intended to further general scientific research understanding and discussion only and are not intended and should not be relied upon as recommending or promoting a specific method diagnosis or treatment by health science practitioners for any particular patient The publisher and the author make no representations or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties including without limitation any implied warranties of fitness for a particular purpose In view of ongoing research equipment modifications changes in governmental regulations and the constant flow of information relating to the use of medicines equipment and devices the reader is urged to review and evaluate the information provided in the package insert or instructions for each medicine equipment or device for among other things any changes in the instructions or indication of usage and for added warnings and precautions Readers should consult with a specialist where appropriate The fact that an organization or Website is referred to in this work as a citation andor a potential source of further information does not mean that the author or the publisher endorses the information the organization or Website may provide or recommendations it may make Further readers should be aware that Internet Websites listed in this work may have changed or disappeared between when this work was written and when it is read No warranty may be created or extended by any promotional statements for this work Neither the publisher nor the author shall be liable for any damages arising herefrom

Library of Congress Cataloging-in-Publication Data

Equine neurology [edited by] Martin Furr Stephen Reed ndash Second edition p cm Includes bibliographical references and index ISBN 978-1-118-50147-4 (cloth)1 HorsesndashDiseases 2 Nervous systemndashDiseases 3 Veterinary neurology I Furr Martin editor II Reed Stephen M editor [DNLM 1 Central Nervous System Diseasesndashveterinary 2 Horse Diseasesndashdiagnosis 3 Nervous System Diseasesndashveterinary SF 959N47] SF959N47E68 2015 6361prime08968ndashdc23

2015007228

A catalogue record for this book is available from the British Library

Wiley also publishes its books in a variety of electronic formats Some content that appears in print may not be available in electronic books

Cover image istockphoto-neuron-impulses 10-01-07 copy ChristianAnthony

Set in 85105pt Meridien by SPi Global Pondicherry India

1 2015

v

Contents

Contributors List vii

Preface ix

Video Clips Demonstrating Clinical Signs x

Section 1 Foundations of Clinical Neurology

1 Overview of Neuroanatomy 3Caroline Hahn and Jerry Masty

2 Cerebrospinal Fluid and the BloodndashBrain Barrier 21Martin Furr

3 Immunology of the Central Nervous System 36Martin Furr

4 Pharmaceutical Considerations for Treatment of Central Nervous System Disease 46Veacuteronique A Lacombe and Martin Furr

5 Fundamental Neurophysiology 58Craig Johnson and Caroline Hahn

Section 2 Clinical Equine Neurology

6 Examination of the Nervous System 67Martin Furr and Stephen Reed

7 Differential Diagnosis and Management of Horses with Seizures or Alterations in Consciousness 79Veacuteronique A Lacombe and Martin Furr

8 Differential Diagnosis of Equine Spinal Ataxia 93Martin Furr

9 Differential Diagnosis and Management of Cranial Nerve Abnormalities 99Robert J MacKay

10 Sleep and Sleep Disorders in Horses 123Joseph J Bertone

11 Headshaking 130Monica Aleman and Kirstie Pickles

12 Differential Diagnosis of Urinary Incontinence and Cauda Equina Syndrome 139Melissa Hines

13 Differential Diagnosis of Muscle Tremor and Paresis 149Amy L Johnson

14 Electrodiagnostic Evaluation of the Nervous System 157George M Strain Frank Andrews and Veronique A Lacombe

15 Anesthetic Considerations for Horses with Neurologic Disorders 184Adriana G Silva

16 The Basics of Equine Neuropathology 191Fabio Del Piero and John L Robertson

17 Diagnostic Imaging of the Equine Nervous System 215Katherine Garrett

Section 3 Specific Disease Syndromes

18 Equid Herpesvirus‐Associated Myeloencephalopathy 225Lutz S Goehring

19 Mosquito‐Borne Infections Affecting the Central Nervous System 233Maureen T Long

20 Contagious Neurological Diseases 262Maureen T Long

21 Bacterial Infections of the Central Nervous System 273Martin Furr

22 Equine Protozoal Myeloencephalitis 285Martin Furr and Daniel K Howe

23 Parasitic Infections of the Central Nervous System 306Martin Furr

24 Miscellaneous Infections of the Central Nervous System 314Martin Furr

25 Disorders Associated with Clostridial Neurotoxins Botulism and Tetanus 319Martin Furr

26 Neurodegenerative Disorders 328Robert J MacKay

27 Equine Hepatic Encephalopathy 343Tom Divers

28 Cervical Vertebral Stenotic Myelopathy 349Amy L Johnson and Stephen Reed

vi Contents

29 Electrolyte Abnormalities and Neurologic Dysfunction in Horses 368Ramiro E Toribio

30 Cervical Articular Process Disease Fractures and Other Axial Skeletal Disorders 386Richard Hepburn

31 Congenital Malformation of the Nervous System 401Martin Furr

32 Central Nervous System Trauma 406Yvette S Nout‐Lomas

33 Disorders of the Peripheral Nervous System 429Martin Furr

34 Equine Neurotoxic Agents and Conditions 437Martin Furr

35 Neonatal Encephalopathy and Related Conditions 455Martin Furr

36 Miscellaneous Movement Disorders 465Caroline Hahn

37 Stereotypic and Behavior Disorders 472Carissa L Wickens and Katherine A Houpt

38 Miscellaneous Conditions 484Martin Furr

Index 488

vii

Contributors List

Monica Aleman MVZ Cert PhD Dip ACVIM (Internal Medicine Neurology)College of Veterinary Medicine

University of California

Davis USA

Frank Andrews DVM MS Dip ACVIMSchool of Veterinary Medicine

Louisiana State University

Baton Rouge USA

Joseph J Bertone DVM MS Dip ACVIMCollege of Veterinary Medicine

Western University

Pomona USA

Fabio Del Piero DVM PhD Dip ACVPSchool of Veterinary Medicine


Baton Rouge USA

Tom Divers DVM Dip ACVIMCollege of Veterinary Medicine

Cornell University

Ithaca USA

Martin Furr DVM Dip ACVIM PhDMarion duPont Scott Equine Medical Center

Virginia‐Maryland Regional College of Veterinary

Medicine

Leesburg USA

Katherine Garrett DVM Dip ACVSRood and Riddle Equine Hospital

Lexington USA

Lutz S Goehring DVM MS PhD Dip ACVIMCollege of Veterinary Medicine

Ludwig Maximillians University

Munich Germany

Caroline Hahn DVM MSc PhD Dip ECEIM Dip ECVN MRCVSRoyal (Dick) School of Veterinary Studies

The University of Edinburgh

Midlothian UK

Richard Hepburn BVSc MS Cert EM(Int Med) Dip ACVIM MRCVSB amp W Equine Hospital

Gloucestershire UK

Melissa Hines DVM Dip ACVIMCollege of Veterinary Medicine

University of Tennessee

Knoxville USA

Katherine A Houpt VMD PhD Dip ACVBCollege of Veterinary Medicine

Cornell University

Ithaca USA

Daniel K Howe PhDGluck Equine Center

University of Kentucky

Lexington USA

Amy L Johnson DVM Dip ACVIMNew Bolton Center

University of Pennsylvania School of Veterinary Medicine

Kennett Square USA

Craig Johnson BVSc PhD DVA Dip ECVAInstitute of Veterinary Animal and Biomedical Sciences

Massey University

Palmerstown North New Zealand

Veacuteronique A Lacombe DVM PhD Dip ACVIM Dip ECEIMCenter for Veterinary Health Sciences

Oklahoma State University

Stillwater USA

Maureen T Long DVM MS PhD Dip ACVIMCollege of Veterinary Medicine

University of Florida

Gainesville USA

Robert J MacKay BVSc PhD Dip ACVIMCollege of Veterinary Medicine


Gainesville USA

viii Contributors List

Jerry Masty DVM MS PhDCollege of Veterinary Medicine

The Ohio State University

Columbus USA

Yvette S Nout‐Lomas DVM MS PhD Dip ACVIM Dip ACVECCCollege of Veterinary Medicine

Colorado State University

Fort Collins USA

Kirstie Pickles BCMS MSc Dip ECEIM PhDScarsdale Equine Veterinary Practice

Derby UK

Stephen Reed DVM MS Dip ACVIMRood and Riddle Equine Hospital

Lexington USA

John L Robertson VMD PhDVirginia Tech


Medicine

Leesburg USA

Adriana G Silva DVM MSFaculty of Veterinary Medicine

University of Montreal

Saint Hyacinthe Canada

George M Strain PhDSchool of Veterinary Medicine


Baton Rouge USA

Ramiro E Toribio DVM MS PhD Dip ACVIMCollege of Veterinary Medicine


Columbus USA

Tim Vojt MACollege of Veterinary Medicine


Columbus USA

Carissa L Wickens PhDDepartment of Animal Sciences


Gainesville USA

ix

Preface

It has been 6 years since the publication of the first edition of Equine Neurology and new information con-tinues to accumulate about equine neurology hence it seems timely to offer the second edition of this work Our goal in the first edition was to provide a compre-hensive review of the field of equine neurology and to structure a textbook that provided not only the clinical descriptions of various equine neurologic disorders but also foundation material to assist in understanding neu-rologic dysfunction in general With the second edition we have attempted to continue in this same theme with the basic organization remaining the samemdash however all chapters have been reviewed modified and updatedmdashsome a little and others more substan-tially In addition we have added chapters on imaging of the nervous system neuronal physiology sleep dis-orders head shaking differential diagnosis of muscle trembling and weakness and cervical articular process

joint disease The chapters on equine neuropathology and electrodiagnostic evaluation have been substan-tially expanded The major change is the inclusion of videos illustrating many of the described conditions These videos were selected to be representative and high‐quality instructional videos to aid the reader in their understanding of the text and equine nervous system disease in general

We wish to acknowledge the hard work and talent of the many individuals who contributed to this work The time commitment necessary to produce high‐quality chapters is substantial and this edition would not have been produced without their hard work and input We hope that you read and study this text use it aid your clinical work and most of all enjoy learning about equine neurology

Martin FurrStephen Reed

x

Video Clips Demonstrating Clinical Signs

This book is accompanied by a companion website

wwwwileycomgofurrneurology

The website includes

bullensp Web exclusive videos

Section 1

Foundations of Clinical Neurology

3

Equine Neurology Second Edition Martin Furr and Stephen Reed

copy 2015 John Wiley amp Sons Inc Published 2015 by John Wiley amp Sons Inc

Companion website wwwwileycomgofurrneurology

1 Overview of NeuroanatomyCaroline Hahn1 and Jerry Masty2

1 Royal (Dick) School of Veterinary Studies The University of Edinburgh Midlothian UK2 College of Veterinary Medicine The Ohio State University Columbus USA

In order to evaluate a patient with a neurologic disorder a basic understanding of the structure and function of the nervous system is necessary The goal of this chapter is not to expose the reader to intricate and perhaps daunting detail but rather to present a basic overview of neuroanatomy highlighting some of the peculiarities of equine neuroanatomy A basic understanding of the nervous system from an anatomic and functional pershyspective is an absolute prerequisite to interpreting the neurological examination and to assess if there is indeed a lesion in the nervous system and if so where the lesion is located (the ldquoanatomic diagnosisrdquo)

Organization of the nervous system

The nervous system is organized into central and perishypheral divisions The central nervous system (CNS) is composed of the brain and spinal cord and is located within the skull and vertebral column The peripheral nervous system (PNS) is formed by neuronal cell processes that extend from the central axis to the periphery There are also collections of neuronal cell bodies in the periphery (ldquogangliardquo) that contribute to the components of the peripheral system Functionally the nervous system is divided into the somatic nervous system a system under voluntary control that innervates skeletal muscle and whose sensory branch reaches consciousness and the autonomic nervous system which is concerned with subshyconsciously regulating visceral smooth muscle structures Both the somatic and nervous system and CNS have central and peripheral motor and sensory components

Development

The nervous system begins as a thickening of the embryonic layer identified as ectoderm The initial growth of the neural ectoderm forms a thickened layer

of cells identified as the neural plate The neural groove is evident as a depression in the neural plate As continued growth of the developing system occurs neural folds develop at the margins of the neural plate caused by migration of the cells in a dorsal direction Eventually the neural folds meet and fuse at the dorsal midline thereby forming a cylindrical structure identified as the neural tube This simplified explanashytion of the formation of the neural tube is shown in Figure 11

As the neural tube is forming cells in the region of the neural folds pinch off and migrate throughout the developing body These are the neural crest cells that differentiate to become various structures in the adult spinal ganglia sensory ganglia associated with some of the cranial nerves autonomic ganglia associated with various body systems cells of the adrenal medulla and interestingly melanocytes

Closure of the neural tube begins in the midsection of the developing embryo and progresses in a cranial and caudal direction The opening at each end of the tube is identified as the neural pore If complete closure of either neural pore is arrested during development conshygenital malformations may be evident after birth such as anencephaly which results in decreased formation of the cerebral hemispheres In extreme conditions the hemispheres may be completely absent Failure of closhysure of the caudal neuropore results in spina bifida This condition presents as varying degrees of lack of closure and fusion of the neural tissue and the bony tissue of the vertebral canal that would normally enclose the caudal portion of the spinal cord

To understand the basic generalized arrangement of the adult nervous system certain facets of development should be kept in mind As the neural tube completes its closure it becomes a fluid‐filled cylindrical structure that serves as the template for further development of the adult structures Segments of the neural tube undergo differential growth to become the adult divisions and

4 Section 1 Foundations of Clinical Neurology

structures of the nervous system As the process of differential growth occurs the fluid‐filled center of the embryonic neural tube follows this pattern of differential growth to become the ventricular system of the nervous system

Embryonic vesiclesThe adult brain is divided into five regions that have their beginnings localized to specific areas of the developing neural tube As the embryonic brain is developing it is characterized by vesicle formation (swellings) that begins to divide the developing brain topographically into separate regions There is a prishymary stage of development where three vesicles are observed This is followed by a secondary stage where five vesicles subsequently form from the initial three Upon further differentiation and growth these five vesicles give rise to the five topographic regions of the adult brain

From rostral to caudal the vesicles of the primary stage are identified as the prosencephalon (foreshybrain) mesencephalon (midbrain) and rhombenshycephalon (hindbrain) With continued differential growth at the rostral end of the neural tube the prosshyencephalon develops into the telencephalon (cereshybrum) and diencephalon (thalamus) At the caudal end of the tube the rhombencephalon gives rise to the metencephalon (pons and cerebellum) and the more caudally positioned myelencephalon (medulla oblongata) (Figure 12)

Ventricular systemThe fluid‐filled cavity of the developing neural tube follows the differential growth pattern of the neural tissue through the vesicle stages into the formation of the adult brain Therefore a portion of the ventricular system is found at all levels of the adult brain as shown in Figure 13

The right and left lateral ventricles follow the growth of the cerebral hemispheres of the cerebrum as they expand dorsally and caudally over the developing brainstem The interventricular foramen interconnects each lateral venshytricle with the third ventricle The third ventricle located in the thalamus is shaped somewhat like an upright tire encircling the interthalamic adhesion (the connection of the left and right halves of the thalamus across the midshyline of the brainstem) In the midbrain the ventricular system is present as the narrow tubular mesencephalic aqueduct Cerebrospinal fluid (CSF) principally produced by the choroid plexus in the lateral and third ventricles flows through the mesencephalic aqueduct to enter the relatively large fourth ventricle The fourth ventricle is a somewhat diamond‐shaped depression of the dorsal medulla oblongata mostly hidden by the overlying cereshybellum CSF leaves the fourth ventricle through lateral apertures at the junction between the midbrain and the medulla oblongata and enters the subarachnoid space that surrounds the brain and spinal cord CSF can also

(a)

1

2

3

4

5

(b)

(c)

(d)

Figure 11 Stages of neural tube formation (a) Thickening of cells to form neural plate (1) (b) Indentation formed by the neural groove (2) (c) Closure of the neural tube produced by neural folds (3) (d) Neural tube (4) closure completed with formation of neural crest cells (5) Circle in (bndashd) represents the notochord

1

2

3

4

5

6

7

(a) (b)

Figure 12 Embryonic brain vesicles (a) Primary vesicle stage (b) secondary vesicle stage 1 Prosencephalon 2 mesencephshyalon 3 rhombencephalon 4 telencephalon 5 diencephalon 6 metencephalon 7 myelencephalon

Chapter 1 Overview of Neuroanatomy 5

enter the central canal of the spinal cord through the median aperture of the caudal extent of the fourth ventricle there is therefor bulk flow of CSF from a cranial to caudal direction with some modification of the fluid content during this passage Hence CSF collected at the lumbosacral junction has slightly different reference values compared with CSF collected at the atlantooccipital site (see Table 11)

Organization of gray and white matter in the CNS

The two main components of the CNS are the brain and the spinal cord In turn the brain and spinal cord are formed by numerous glial cells a rather smaller number of neurons and neuronal processes (axons with or without surrounding myelin) Cell bodies of neurons and their unmyelinated processes have a somewhat gray appearance and not surprisingly form the gray matter of the nervous system White matter of the nervous system is formed by myelinated axons of the neurons The gray and white matter of the nervous system is organized differently in the brain and spinal cord gray matter of the cerebrum is found either on its surface where it is identified as cortical gray matter or as collecshytions of neuronal cell bodies located deep to the surface the basal nuclei Neurons within a particular cluster generally perform the same function and in the CNS are called nuclei

1

3

4

5

6

7

2

Figure 13 Dorsal view of ventricular system 1 Lateral ventricles 2 interventricular foramen 3 third ventricle 4 mesencephalic aqueduct 5 fourth ventricle 6 lateral aperture 7 extension of ventricular system into central canal of spinal cord

Table 11 Functional classification of the cranial nerves

Cranial nerve Number Function

Sensory

Olfactory CN I Olfaction

Optic CN II Vision

Vestibulocochlear CN VIII Balance and hearing

Motor

Oculomotor CN III Extraocular eye muscles

Parasympathetic to eye

Trochlear CN IV Extraocular eye muscles

Abducens CN VI Extraocular eye muscles

Accessory CN XI Pharyngeal and laryngeal muscles cervical muscles

Hypoglossal CN XII Lingual muscles

Mixed

Trigeminal CN V General sensation to face motor to muscles of mastication

Facial CN VII Taste sensation motor to muscles of facial expression parasympathetic for salivation and

lacrimation

Glossopharyngeal CN IX Pharyngeal sensation taste swallowing muscles parasympathetic for salivation

Vagus CN X Sensation pharynx and larynx swallowing parasympathetic for thoracic and abdominal organs


The white matter of the cerebrum is organized into bundles that form a system of conduction pathways to from and within the cerebrum Three types of white matter fiber systems are recognized consisting of proshyjection fibers commissural fibers and association fibers The critically important projection fibers carry information to and from the cerebrum to form connecshytions with the brainstem and spinal cord principally through the internal capsule Commissural fibers carry information across the midline between the left and right cerebral hemispheres mostly through the prominent corpus callosum Association fibers form more subtle pathways that connect structures within one hemisphere within and between lobes A lobe of

the brain refers to a region of the cortex that tends to have some functional specificity and is named toposhygraphically for the overlying bone of the skull Therefore the frontal parietal occipital and temporal lobes are identified deep to the skull bone of the same name

Gray matter in the brainstem is arranged in columns of cells with broadly similar functions often broken into nuclei of neurons with an even more specific function Thus the ventrally located somatic motor column of neurons is arranged into nuclei that innervated specific cranial nerves associated with specific functions such as cranial nerve V for innervation of the muscles of masticashytion and cranial nerve VII for innervation of muscles of facial expression A similar arrangement is evident for the medially located column consisting of parasympathetic autonomic neurons innervating for example the constrictor muscles of the pupil (cranial nerve III) or the lacrimal glands (cranial nerve VII) (see Figure 14) Furthermore more dorsal structures tend to be sensory while those on the ventral aspect tend to have motor functions this arrangement is followed through into the gray columns of the spinal cord whereby the neurons of the dorsal horns are principally sensory while the ventral horns comprise motor neurons In the thoracic and lumbar segments of the spinal cord an additional column is present in a lateral position approximately midway between the dorsal and ventral columns This lateral horn of gray matter contains cell bodies that function as the presynaptic (preganglionic) lower motor neurons (LMNs) in the autonomic nervous system

The anatomic segregation of sensory and motor cells can be appreciated in the embryonic spinal cord as shown in Figure 15 The dorsal half of the developing gray

1

2

3

Figure 15 Neuron segregation in the developing spinal cord (schematic) 1 Alar plate containing sensory neurons 2 sulcus limitans 3 basal plate containing motor neurons

1

106

7

14

8

15

1112

16

13

9

2

4

5

3

Figure 14 Schematic view of the dorsal brainstem Sensory nuclei are indicated on the left motor nuclei on the right Motor nuclei with similar shading form functional groups for target structures as described in the text 1 Mesencephalic nucleus of the trigeminal nerve 2 pontine sensory nucleus of the trigeminal nerve 3 spinal nucleus of the trigeminal nerve 4 vestibular and cochlear nuclei 5 solitary nucleus 6 oculomotor nucleus 7 trochlear nucleus 8 abducens nucleus 9 hypoglossal nucleus 10 parasympathetic nucleus of the oculomotor nerve 11 parasympathetic nucleus of the facial nerve 12 parasympathetic nucleus of the glossopharynshygeal nerve 13 parasympathetic nucleus of the vagus nerve 14 motor nucleus of the trigeminal nerve 15 motor nucleus of the facial nerve 16 nucleus ambiguus


matter is identified as the alar plate neurons in this region will become the sensory neurons in the dorsal gray column in the adult spinal cord The ventral half of the gray matter is referred to as the basal plate neurons in this region will become the motor neurons in the venshytral column of gray matter The hollow portion of the embryonic tube will persist in the adult spinal cord as its central canal There is a slight evagination within the central embryonic cavity identified as the sulcus limitans and this serves as a dividing line between the sensory and motor neurons of the developing spinal cord

Spinal cord white matter (Figure 16) meanwhile is located superficial to the gray columns and is arranged into large bundles called funiculi which are organized by function Dorsal funiculi for the most part carry sensory information to the forebrain lateral funiculi connect the spinal cord and the cerebellum and ventral funiculi principally consist of somatic motor axons on their way to synapse with LMNs in the ventral horn of the spinal cord

Organization of gray and white matter in the PNS

The PNS is located peripheral to the skull and vertebral column By convention a cluster of neuronal cell bodies located outside the CNS is called a ganglion and consist of somatic sensory and autonomic motor neurons that is there are no somatic motor neurons outside of the CNS Equine spinal ganglia are easily identified on dissection while those associated with the sensory branches or cranial nerves tend to be much smaller An exception is the trigeminal ganglion in the base of the skull which is comparatively enormous

The white matter of the peripheral system is comshyposed of axons covered by Schwann cells and may be myelinated or unmyelinated somatic or autonomic

Gross anatomy of the CNS

An overview of the surface anatomy of the brain is described here Readily observed structures of each of the five adult divisions of the brain will be highlighted From rostral to caudal the divisions of the brain are the medulla oblongata pons and cerebellum midbrain thalamus and cerebrum As each division is described the reader should refer to the diagrams of the ventral surface of the brain (Figure 17) the dorsal surface of the brainstem (Figure 18) and the median section of the brain (Figure 19) to see the location of the referenced structures

1

2

3

4

5

6

Figure 16 Arrangement of gray and white matter in the spinal cord 1 Dorsal gray column 2 lateral gray column 3 ventral gray column 4 dorsal funiculus 5 lateral funiculus 6 ventral funiculus

1

2

34

5

6

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25

8

9

10

11

12

13

14

15

16

1718

26

27

28

29

19

20

21

22

23

24

Figure 17 Ventral view of the brain (schematic) 1 Olfactory bulb 2 olfactory peduncle 3 lateral olfactory tract 4 lateral rhinal sulcus 5 piriform lobe 6 optic nerve 7 optic chiasm 8 optic tract 9 tuber cinereum 10 hypothalamus 11 mammillary body 12 oculomotor nerve 13 interpedunshycular fossa 14 crus cerebri 15 trochlear nerve 16 trigeminal nerve 17 abducent nerve 18 facial nerve 19 vestibulocoshychlear nerve 20 glossopharyngeal nerve 21 vagus nerve 22 accessory nerve 23 hypoglossal nerve 24 spinal root of accessory nerve 25 transverse fibers of the pons 26 trapezoid body 27 cerebellum 28 pyramid 29 ventral median fissure


Cerebrum (telencephalon)The telencephalic vesicle in the developing embryo gives rise to the cerebrum formed by the left and right cerebral hemispheres The cerebrum is the large superstructure that is connected to and covers the rostral brainstem On the ventral surface the olfactory bulbs are located at the rostral limit of each hemisphere Olfactory receptors located in the nasal cavity transmit impulses along the olfactory nerve ((cranial nerve (CN) I) to synapse in the olfactory bulbs The name olfactory ldquonerverdquo is actually a misnomer since it consists entirely of CNS tissue but in humans is so diminutive as to resemble a nerve The olfactory tract is visible on the ventral surface in its posishytion between the olfactory bulbs and the piriform lobe of the cerebrum These olfactory structures contribute to the formation of that part of the cerebrum identified as the rhinencephalon for processing olfactory information this is demarcated from the rest of the cerebral cortex by the lateral rhinal sulcus

The surface of the cerebrum is characterized by ridges identified as gyri and grooves identified as sulci The left and right cerebral hemispheres are separated along the midline by the longitudinal cerebral fissure while the caudal aspect of each hemisphere is separated from the cerebellum by the transverse cerebral fissure The surface of the cerebrum is divided into lobes that are named topographically for the overlying bone of the skull the cerebral lobes are thus identified as frontal parietal temporal and occipital each with broad functional specificities but no very detailed anatomical delineation A greatly simplified listing of cerebral function suggests the following associations the frontal lobe in horses is likely the motor cortex and association area involved in planning actions and movement The parietal lobe is found just caudal to the motor cortex and consists of somesthetic regions and cognitive association areas involved in perceiving sensory input while auditory information is processed in the temporal lobe ventrolateral to the parietal lobe The occipital lobe processes visual information

CSF within the respective cerebral hemispheres is contained in the left and right lateral ventricles which intercommunicate at the midline with the third venshytricle through the small interventricular foramen

Thalamus (diencephalon)The thalamus is located rostral to the midbrain and is part of the forebrain and not the brainstem Strictly speaking the anatomical structure is best termed the

10 11 12 13

14

1516171819

4321

5

6 89

7

Figure 19 Median section of the brain (schematic) 1 Olfactory bulb 2 optic nerve 3 optic chiasm 4 hypothalshyamus (pituitary gland removed) 5 interthalamic adhesion 6 corpus callosum 7 lateral ventricle 8 hippocampus 9 fornix 10 habenula 11 pineal body 12 rostral colliculus 13 caudal colliculus 14 cerebellum 15 fourth ventricle 16 arbor vitae (cerebellar white matter) 17 pons 18 mesenshycephalic aqueduct 19 third ventricle

1

2

3

4

5

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7

8

12

13

1415

16

17

18

19

9

1011

IV

Figure 18 Dorsal view of the brainstem (schematic) 1 Stria habenularis thalami 2 thalamus 3 lateral geniculate body 4 pineal body 5 medial geniculate body 6 rostral colliculus 7 caudal colliculus 8 trochlear nerve 9 middle cerebellar peduncle 10 caudal cerebellar peduncle 11 rostral cerebellar peduncle 12 vestibulocochlear nerve 13 sulcus limitans 14 median sulcus 15 obex 16 cuneate tubercle 17 fascicshyulus gracilis 18 fasciculus cuneatus 19 spinal tract of the trigeminal nerve


diencephalon which is composed of five separate parts thalamus epithalamus metathalamus hypothalamus and subthalamus The largest portion of this however is the thalamus and it is reasonable to refer to this strucshyture by that name

On the ventral surface of the thalamus is found the hypothalamus bounded by the mammillary bodies caushydally and the optic chiasm rostrally The pituitary gland is attached to the hypothalamus by the tuber cinereum a slightly elevated ridge of hypothalamic tissue between the two landmarks identified earlier but because it is firmly adhered to the skull the pituitary is rarely removed along with the brain The mammillary bodies appear as the two small prominences and are the most caudally located structures of the ventral surface of the thalamus These act as relay stations interconnecting olfactory behavioral and autonomic areas of the brain The optic nerve (CN II) fibers enter at the rostral edge of the diencephalon and form the optic chiasm Calling this structure a ldquonerverdquo is strictly speaking incorrect as it is merely an extension of the brain with axons surrounded by oligodendrocytes not Schwann cells

The dorsal surface of the thalamus is visible once the cerebrum has been removed The left and right lateral geniculate nuclei are dorsocaudal projections at the most caudal margin of the thalamus and are vital relay stations that send information into the cerebrum Slightly ventral to each lateral geniculate nucleus on either side are the medial geniculate nuclei which send auditory information to the cerebrum On the caudal dorsal surface of the thalamus is found a small unpaired prominence so important in regulating mare seasonal reproduction the pineal gland

At the level of the thalamus the ventricular system resembles a tire which encircles the median section of the thalamus This is where the left and right divisions of the thalamus are joined across the midline by thalamic tissue identified as the interthalamic adhesion A midsagshyittal view of the brainstem in Figure 19 reveals the third ventricle encircling the interthalamic adhesion

Midbrain (mesencephalon)A further prominent division of the brain is midbrain Ventrally it is covered by conspicuous bundle fibers known as the crus cerebri These relatively large bundles are formed by fibers of the motor system as they pass through the midbrain to reach the pyramids in the caudal portions of the brainstem The oculomotor nerve (CN III) emerges from the ventral surface of the mesencephshyalon The mesencephalic aqueduct is that part of the ventricular system located in the mesencephalon and interconnects the third and fourth ventricles

The dorsal surface of the mesencephalon is charactershyized by two pairs of rounded prominences the rostral and caudal colliculi (ldquohillockrdquo) Each rostral colliculus serves as a synaptic site in the pathway for visual

reflexes while the caudal colliculus serves as a synaptic site in the pathway for auditory reflexes activity The region of the midbrain dorsal to the mesencephalic aqueduct is known as the tectum and tectospinal tracts running from the tectum to LMNs in the spinal tract regulate movement associated with auditory reflexes and visual reflexes

The other cranial nerve associated with the midbrain is the trochlear nerve (CN IV) and unusually the fibers from that nucleus emerge from the dorsal surface of the mesencephalon and cross to reach the opposite ventral surface of the brainstem as it travels toward the orbit

Pons (ventral metencephalon)Moving caudally the next division of the brain is the pons The ventral surface is formed by the transverse fibers of the pons a wide bundle of fibers that transmits information from the forebrain to the cerebellum As the transverse fibers of the pons move laterally and dorshysally they form the middle cerebellar peduncle which can be seen entering into the cerebellum The only nucleus in the pons is the prominent motor nucleus of the trigeminal nerve It innervates the muscles of mastishycation and is not infrequently affected by Sarcocystis neurona (the causative agent of equine protozoal myeloshyencephalitis) The large trigeminal nerve (CN V) leaves the ventral surface of the pons at the rostral edge of the transverse fibers of the pons

Cerebellum (dorsal metencephalon)The cerebellum (ldquolittle brainrdquo) is the superstructure seen on the dorsal surface of the pons Embryologically this is part of the metencephalon however it is not considshyered part of the brainstem The role of the cerebellum is to monitor sensorimotor information that travels through the nervous system and it acts to integrate this information to produce smooth coordinated movement It is separated from the cerebrum by an intervening space in which lies the bony tentorium cerebelli an immovable object under which the brain can herniate with devastating consequences should disease result in swelling of the neural structures rostral or caudal to it

Anatomy of the cerebellumThe cerebellar surface is divided into a midline strip the vermis and the tissues lateral to the vermis are the left and right cerebellar hemispheres The cerebellar surface is characterized by alternating grooves and ridges of tissue identified as the sulci and folia respectively As a general guideline the primary fissure separates the rosshytral lobe of the cerebellum from the caudal lobe on the dorsal surface On the ventral surface the caudolateral fissure separates the caudal lobe of the cerebellum from the flocculonodular lobe (Figure 110)

Figure 111a b shows that the anatomic arrangeshyment of the gray and white matter in the cerebellum


is analogous to the arrangement that was seen in the cerebrum Gray matter composed of a staggering number of small neurons covers the cerebellar corshytical surface that surrounds the deeper white matter The cortical gray matter is dived into three layers From superficial to deep these layers are identified as the molecular Purkinje and granular layer Significantly Purkinje fibers are the only neurons whose axons send efferent information from the cershyebellar cortex Subcortical gray matter is innervated by the Purkinje neurons and appears as three pairs of cerebellar nuclei embedded in the white matter From medial to lateral these deep cerebellar nuclei are identified as the fastigial interpositus and lateral nuclei respectively

Three pairs of cerebellar peduncles connect the cereshybellum to the brainstem From lateral to medial these stalk‐like connections are identified as the middle caudal and rostral cerebellar peduncles (ldquofeetrdquo) respectively (Figure 18) The peduncles are named based on their connections to the brainstem not on their position relative to each other Therefore the middle cerebellar peduncle is the most lateral of the three and has been described previously as fibers that represent the continshyuation of the transverse fibers of the pons carrying information into the cerebellum The caudal cerebellar

peduncle is so named because it is formed by various tracts that pass through the caudal portion of the brainshystem to reach the cerebellum The most medial of the cerebellar peduncles is the rostral cerebellar peduncle It solely carries efferent fibers originating in the cereshybellum that travel rostrally into the brainstem As a general rule of thumb the caudal cerebellar peduncle carries a majority of fibers that represent afferent tracts

987

6

1 3

45

6

2

(a)

(b)

1 2345

Figure 111 (a) Schematic view of the sagittally sectioned cerebellum Inset shows cerebellar cortical layers 1 Rostral lobe 2 primary fissure 3 caudal lobe 4 caudolateral fissure 5 flocculonodular lobe 6 white matter (arbor vitae) 7 granular layer 8 Purkinje cell layer 9 molecular layer (b) Schematic view of transversely sectioned cerebellum dorsal to the brainstem 1 Cerebellar gray matter 2 cerebellar white matter 3 fastigial nucleus 4 interpositus nucleus 5 lateral nucleus

12

5

6

8

10

9

7

3

4

Figure 110 Schematic view of the cerebellum indicating anatomic regions The cerebellum has been ldquounfoldedrdquo with the flocculonodular lobe positioned at the bottom of the diagram 1 Vermis 2 hemisphere 3 intermediate hemishysphere 4 primary fissure 5 rostral lobe 6 caudal lobe 7 caudolateral fissure 8 flocculonodular lob 9 flocculus 10 nodulus


entering the cerebellum and the rostral cerebellar peduncle primarily carries fibers that represent efferent tracts leaving the cerebellum

Functional organization of the cerebellumWhile the cerebellum is a complex structure in terms of its role in the nervous system a simplified overview can be presented to gain a fundamental understanding of cerebellar function The cerebellum receives general proprioceptive information from the periphery along with information from both the pyramidal and extra motor systems Information about head position and movement also enters the cerebellum

The Purkinje cells in the cortex monitor and process all the incoming information When activated as a result of the net summation of all the afferent impulses the Purkinje cells send normally inhibitory impulse to the appropriate cerebellar nuclei The cerebellar nuclei in turn stimulate upper motor neurons (UMNs) in the brainstem which in turn project to LMNs in the spinal cord as well as the cerebral cortex to produce coordishynated movement

While there is some degree of overlap it is possible to correlate functional areas of the cerebellar lobes with the type of movement that is regulated and coordishynated The flocculonodular lobe (Figure 110) on the ventral surface of the cerebellum maintains balance and equilibrium and controls head and conjugate eye moveshyments through the input of the vestibular system This part of the cerebellum is identified as the vestibulocershyebellum The vermis and paravermal areas of the cereshybellum coordinate activity for muscle tone and posture control and functionally are identified as the spinocershyebellum Finally the cerebellar hemispheres lateral to the intermediate zone are known as the cerebrocerebelshylum as they coordinate voluntary and highly skilled movement

Neurologic signs of cerebellar dysfunctionAlthough this is a greatly simplified explanation of cerebellar connections it is through these complex interactions that the cerebellum monitors motor proprioceptive and vestibular (balance) information to maintain muscle tone and equilibrium and produce smooth coordinated movement The clinical signs of cerebellar disease can be related to the area of the cerebellum that has been affected and results in loss of its regulatory ability The most common signs of cereshybellar dysfunction relate to the function of the spinocershyebellum and a loss of inhibition of UMNs due to a loss of inhibitory Purkinje cell output This results in increased range of movement (hypermetria) and increased tone (spasticity) If the vestibulocerebellum is involved either directly or indirectly by altered input from the vestibular system then vestibular signs such as a swaying posture

wide‐based stance nystagmus and ventral strabismus may be noted A loss of feedback pathways between the cerebrocerebellum and the forebrain results in asynshychrony in movements and clinical signs of overshooting of body parts as well as tremor that is exacerbated as the animal attempts to make a voluntary movement (intenshytion tremor)

Medulla oblongata (myelencephalon)The medulla oblongata is the most caudal part of the brainstem located between the trapezoid body rostrally and the junction of the brainstem with the spinal cord at the level of the emergence of the first cervical spinal nerve The ventral median fissure divides the ventral surface into right and left halves Immediately adjacent to the fissure are the fiber bundles identified as the pyrshyamids The pyramids consist of descending motor fibers traveling through the brainstem Given the lack of a corshyticospinal tract in equids (see ldquoDescending tracts of the spinal cordrdquo) it is likely that the pyramidal tracts consist of fibers destined for LMNs in cranial nerve nuclei the so‐called corticonuclear fibers The rectangular‐shaped trapezoid body at the rostral edge of the medulla oblonshygata is formed by fibers associated with the auditory system The fibers of cranial nerves VI through XII exit the brainstem on the ventral surface of the medulla oblongata

The caudal portion of the medulla oblongata is a tubular structure but the rostral portion is open dorshysally and forms the fourth ventricle Three white matter fiber bundles occupy the dorsal surface beneath the ventricle the bundle closest to the midline is the fascicshyulus gracilis formed by fibers that carry conscious proshyprioceptive impulses from the pelvic limb to the forebrain via the thalamus Just lateral to the fasciculus gracilis is the fasciculus cuneatus which transmits simshyilar fibers arising from the thoracic limbs Moving latershyally the next bundle is the spinal tract of the trigeminal nerve this tract is formed by fibers that carry nocicepshytive information from the head to conscious perception by the forebrain

The rostral portion of the fourth ventricle lies in the dorsal pons and the caudal half makes up the dorsal portion of the rostral medulla oblongata The roof of the fourth ventricle is formed by the rostral and caudal medullary velum These are a thin membranous covshyering made up of ependymal and pial cells of the meninges respectively located rostral and caudal to the cerebellum respectively and function to prevent the escape of CSF into the subarachnoid space The caudal angle of the fourth ventricle forms a topographic landshymark identified as the obex and the groove along the midline in the floor of the ventricle that separates the two halves of the medulla oblongata is called the median sulcus


Topographic features of the spinal cord

Since a large number of neurologic cases presenting to clinicians do so due to lesions to the spinal cord it behooves clinicians to have a good understanding of the functional neuroanatomy relating to this structure The white matter of the spinal cord is formed by ascending and descending pathways that transmit sensory and motor information through the nervous system Ascending pathways originate in the spinal cord and travel to higher levels in the brain Analogously descendshying pathways that regulate motor activity originate in higher levels of the brain and descend through the CNS to reach spinal cord levels Details of pathways are shown in Figure 112 but it is worth remembering that these repshyresent extrapolations from other better studied species

The spinal cord is divided into left and right halves by the dorsal median sulcus and the ventral longitudinal fissure as shown in Figure 113 The spinal cord is composed of gray and white matter with the white matter superficial to the deeper embedded gray matter Large bundles of white matter in the spinal cord are identified as funiculi Each funiculus in turn is formed by smaller bundles of white matter identified as the various ascending or descending tracts of the spinal cord Spinal nerve roots enter and leave the spinal cord dividing it in a segmental manner

The left and right dorsal roots enter the spinal cord at the dorsolateral sulcus the large bundle of white matter located between the dorsal roots is the left and right dorsal funiculus Fibers located in the dorsal funiculus of the spinal cord are predominately fibers for conscious proprioception heading to the thalamus and subseshyquently the forebrain The dorsal funiculus is further divided by the intermediate sulcus into the fasciculus gracilis medially and the fasciculus cuneatus laterally the fasciculus gracilis carries information related to conshyscious proprioception from the pelvic limb while the fasciculus cuneatus carries information related to conshyscious proprioception from the thoracic limbs The function of the dorsal funiculus is described in the secshytion on conscious proprioception

The lateral funiculus is the large bundle of white matter located between dorsal and ventral roots on either half of the spinal cord The principle components of the lateral funiculus are the spinocerebellar tracts that is fibers running from the spinal cord to the cereshybellum for subconscious proprioception These are important components of the subconscious propriocepshytive system discussed later

The ventral funiculus is located between the ventral roots It is also formed by a mixture of ascending and descending tracts This principally consists of descending tracts carrying UMN axons to the LMNs further caudal in the spinal cord

The peripheral nervous system

Peripheral nerves transmit a mix of sensory and motor information Sensory impulses are detected by numerous and varied nerve receptors in the periphery

13

12

11

10

1415

8

65

4

3

2

9

Figure 112 Position of ascending and descending tracts in the spinal cord (schematic) Descending tracts are numbered on the right ascending tracts are numbered on the left 2 Rubrospinal tract 3 medullary reticulospinal tract 4 lateral vestibulospinal tract 5 pontine reticulospinal tract 6 tectoshyspinal tract 8 medial longitudinal fasciculus 9 spinothalamic tract 10 ventral spinocerebellar tract 11 fasciculus proprius (contains ascending and descending fibers) 12 dorsal spinocerebellar tract 13 dorsolateral fasciculus (Lissauerrsquos tract) 14 fasciculus cuneatus 15 fasciculus gracilis

1 23

4

5

6

78

9

10

11

Figure 113 Spinal cord crossshysection (schematic) The fiber of a sensory neuron is shown as it enters the spinal cord through the dorsal root The fiber of a motor neuron is shown as it leaves the spinal cord through the ventral root 1 Median sulcus 2 dorsal intermediate sulcus 3 dorsolateral sulcus 4 dorsal root 5 spinal ganglion 6 spinal nerve proper 7 ventral root 8 ventral median fissure 9 ventral funiculus 10 lateral funiculus 11 dorsal funiculus


and are transmitted toward the CNS while motor impulses originate in LMNs of the CNS and travel through the peripheral nerves to provide motor innershyvation to somatic or visceral target structures of the body The combined motor neuron soma peripheral nerve neuromuscular junction and muscle are called a motor unit and dysfunction of any portion of the motor unit will result in paresis with diminished reflexes and decreased muscle tone

There are two broad categories of peripheral nerves spinal nerves and cranial nerves Both perform the same function of transmitting sensory and motor innershyvation between the CNS and peripheral structures with the distinction between spinal and cranial nerves being simply their anatomic location At the level of the spinal cord each spinal nerve is attached to the cord by dorsal and ventral roots The dorsal root of the spinal cord repshyresents the equivalent of axonal processes that origishynated from sensory cell bodies located in the spinal ganglion as shown in Figure 114 The ventral root is formed by axons that originated in large motor neuron soma located in the spinal cord ventral gray column and leave the spinal cord to innervate target structures in the periphery The spinal nerve proper is a relatively short segment located at the level of the intervertebral foramen At this level the spinal nerve is composed of the intermingling of nerves of sensory nerve fibers from peripheral nerve receptors and the motor nerve fibers traveling to peripheral target structures The spinal nerve divides into dorsal and ventral branches that carry sensory and motor impulses throughout the periphery

Afferent function of peripheral nervesSpinal and cranial peripheral nerves will transmit afferent (sensory) information from somatic and visceral structures This includes impulses of nociception temshyperature touch position and movement that is nocishyception and proprioception and autonomic impulses that originate within body viscera related to temperashyture blood pressure gas and chemical concentrations and dilation pressure and movement of the body organs For the spinal division of peripheral nerves the sensory cell bodies are segmentally distributed and located in the spinal ganglia Axons from these primary sensory cells generally synapse in the dorsal gray column and then ascend to higher centers in the nervous system

Sensory information from the head is transmitted by specific cranial nerves (see Table 11) Proprioceptive and nociceptive information from the head travels through the trigeminal nerve (CN V) This information is processed through a column of cells in the brainstem identified as the trigeminal sensory nucleus Sensory afferents for balance and equilibrium travel through the vestibular portion of the vestibulocochlear nerve and synapse in the brainstem in the vestibular nuclei The cochlear division of the vestibulocochlear nerve carries auditory afferents that synapse in the brainstem cochlear nuclei Autonomic afferent (via glossopharyngeal and vagus nerves) and taste fibers (via the facial nerve and glossopharyngeal nerve) synapse in another large sensory nucleus of the brainstem the solitary nucleus Afferent impulses for vision travel through the optic nerve (CN II) and synapse in the lateral geniculate nucleus of the thalamus Sensory input for olfaction travels through the olfactory nerve (CN I) to synapse in the olfactory bulb of the rhinencephalon These sensory cranial nerve nuclei are presented in Figure 14

Efferent function of peripheral nervesMotor neurons are distributed along the length of the spinal cord in the ventral gray column Motor fibers leave the spinal cord to travel through the spinal nerve to provide innervation to the skeletal muscles in the body Motor innervation to the muscles of the head travels through various cranial nerves Motor nerve fibers travel through select cranial nerves to provide autonomic innervation The cranial nerves with motor function originate from nuclei scattered throughout the brainstem The cells of the motor nuclei are arranged in three fragmented columns that can be functionally organized based on their target structures as described later and shown in Figure 14

Autonomic system targetsThe target structures for this group are glandular tissue and cardiac and smooth muscle cells that receive parasympathetic motor innervation via the cranial

1

2

3

4 5

6

Figure 114 Spinal nerve anatomy The dorsal root is formed by sensory neurons the ventral root is formed by motor neurons Arrowheads indicate sensory impulses travel toward the spinal cord and motor impulses travel toward the periphery 1 Dorsal root 2 spinal ganglion (dorsal root ganglion) 3 ventral root 4 spinal nerve proper 5 dorsal branch of the spinal nerve 6 ventral branch of the spinal nerve


nerves The efferent motor fibers originate in the parasympathetic motor nuclei of cranial nerves III VII IX and X A summary of cranial nerve function is found in Table 11

Functional systems for clinicians

Neurological cases generally are presented to clinicians not with a complaint within a specific structure of the nervous system instead clinical signs are primarily related to a functional system be it paresis due to a lesion in the motor system ataxia due to a deficit in general proprioception or the vestibular system or a clinical sign related to the autonomic nervous system Having an understanding of the organization of the nershyvous system provides the basis for understanding the disorders that affect the various components of the nershyvous system The sensory and motor pathways (and associated clinical signs) that will be reviewed in the folshylowing sections include the somatic motor system (paresis) general proprioception (ataxia) nociception (pain perception) vestibular system (vestibular ataxia) and the autonomic system

Somatic motor systemThe control of voluntary movements is complex Many different systems across numerous brain areas need to work together to ensure proper motor control Neurons of the motor system send their axons from higher levels of the CNS to regulate and influence the activity of the motor neurons in the brainstem and spinal cord that leave the CNS to innervate target structures in the periphery Motor neurons in the higher levels of the CNS are defined as upper motor neurons and motor neurons that send their axons to provide motor innershyvation to peripheral targets are defined as lower motor neurons The descending tracts of the spinal cord are formed by axons of UMNs that descend through the brain and spinal cord to provide a regulatory influence on the lower motor cells The descending tracts of the spinal cord are shown opposite the ascending tracts in Figure 112 Unlike the autonomic system there is only one LMN in this chain that is one UMN synapses (directly or indirectly) with one LMN whose axon then influences a number of skeletal muscle fibers in the periphery Damage to UMNs or LMNs result in the inability to initiate movement or bear weight (ie paresis) but the quality of the paresis is different for the two and will be described in the subsequent section

In primates the UMN system is organized into two components the pyramidal motor system responsible for fine isolated precise and specific movements and the extrapyramidal system responsible for gross

synergic movements which require the activity of large groups of muscles There is no evidence that horses have significant pyramidal tracts in the spinal cord the only direct motor cortex to LMN pathways in equids likely terminates in the brainstem and so this system will not be reviewed further

Extrapyramidal motor organizationThe extrapyramidal motor system is so named because the nuclei and tracts contained within this division do not contribute to formation of the pyramids seen on the ventral surface of the medulla oblongata Anatomically the extrapyramidal part of the motor system is comshyposed of a myriad of nuclei and tracts located within all divisions of the brain In general the extrapyramidal system principally provides regulatory influence on the LMNs that are responsible for muscle tone and posture The mechanism for the maintenance of muscle tone is further described in Chapter 36 and Figure 361

UMN nuclei in the brainExtrapyramidal structures are widespread throughout the CNS and provide multiple polysynaptic pathways to ultimately regulate the activity of LMNs The cerebrum contains cortical and subcortical collections of extrapyshyramidal motor cells and further nuclei are found in the brainstem

Motor neurons in the cerebral hemisphere are scatshytered in the cerebral cortex but also in the gray matter deep to the cortex in the basal nuclei The nuclei of sigshynificance are the caudate nucleus putamen and globus pallidus White matter between the caudate nucleus and the putamen appear grossly as stripes and the collective term for those two nuclei is the corpus striatum (Figure 115) Generally speaking within the processing network of the corpus striatum the caudate nucleus and the putamen act as afferent centers that receive and process information The globus pallidus acts as an efferent center to send information to other extrapyramidal censhyters in the thalamus and brainstem

Many motor nuclei are also found within the brainshystem In the midbrain the major extrapyramidal nuclei are the red nucleus the tegmental nucleus and the subshystantia nigra Of these three the red nucleus is of particular importance It gives rise to the rubrospinal tract that descends through the rest of the brainstem and the lateral funiculus in the spinal cord to reach the LMNs of the spinal cord In the pons a nuclear area deep in the reticular formation plays a role in extrapyramidal regushylation and the medullary reticular nucleus is located in the reticular formation of the medulla oblongata

Although the extrapyramidal motor system is characshyterized by numerous structures descending regulation likely reaches the LMNs in the spinal cord mainly


through three contralateral pathways the rubrospinal tract of the midbrain the pontine reticulospinal tract and the medullary reticulospinal tract (See Figure 112)

Neurologic signs of UMN dysfunctionUMNs regulate LMNs both initiating movement and of principal importance in the extrapyramidal system regulating tone Indeed the vast majority of UMN axons function to inhibit extensor tone A lesion that involves UMN structures or pathways essentially decreases or eliminates the regulatory control of the UMN on the LMN resulting in increased extensor tone and reflexes and diminished ability to initiate voluntary movements The clinical signs that are considered to be hallmarks of UMN disease include hypertonus (ldquospasshyticityrdquo) hyperreflexia (commonly examined in small animals but almost impossible to elicit in ambulatory adult horses) and UMN paresis The most straightforshyward way to test for UMN paresis in horses is to firmly and consistently pull on the horsersquos tail as it is walking in a straight line an animal with UMN paresis will not be able to initiate the ipsilateral limb extension required

to counteract this maneuver and particularly patients with acute spinal cord compression can be remarkably easy to pull over UMN paresis differs from LMN paresis by the preservation and often increase of reflexes and muscle tone

Somatic sensory systemsThere are two principal sensory systems of the body a system responsible for detecting body position and a system responsible for detecting the sensation of noxshyious stimuli These two functional systems are defined as proprioception and nociception respectively The major pathways that monitor proprioception and nocishyception are described as follows

General proprioceptionDefinition of general proprioception and ataxiaGeneral proprioception is a sensory system that detects the state of the position and the movement in muscles and joints The clinical sign resulting from a deficit in general proprioception is called ldquoataxiardquo an inconsisshytent gait with alterations in the rate range and force

(a)

12

3

45

6

7

(b)

1

2

34 5

678

9101112

13

Figure 115 (a) Transverse section of the brain at the level of the mammillary body showing the corpus striatum 1 Lateral ventricle 2 caudate nucleus 3 internal capsule 4 globus pallidus (pallidum) 5 putamen 6 corpus callosum 7 hippocampus (b) Schematic topographic organization of extrapyramidal motor centers Nuclei 6 7 and 8 are in the diencephalon 9 10 and 11 are in the midbrain 12 is in the pons and 13 is in the medulla oblongata 1 Cerebral cortex 2 caudate nucleus 3 globus pallidus (pallidum) 4 putamen 5 thalamus 6 zona incerta 7 endopeduncular nucleus 8 subthalamic nucleus 9 red nucleus (arrow represents rubrospinal tract that decussates and descends to spinal cord levels) 10 tegmental nucleus 11 substantia nigra 12 pontine reticular nucleus (arrow represents pontine reticulospinal tract that decussates and descends to spinal cord levels) 13 medullary reticular nucleus (arrow represents medullary reticulospinal tract that decussates and descends to spinal cord levels)


of movement An ataxic gait is characterized by being inconsistent and having components of hypometria (too little joint movement spasticity) and hypermetria (high striding) movement Depending on the nature of the lesion hypometria or hypermetria may predomishynate Ataxia is purely due to a deficit in proprioception not strength however since the majority of cases have spinal cord compression with lesions in the UMN system also signs of both UMN paresis and ataxia are expressed together Balance is a further proprioceptive system and a lesion in the vestibular system also results in ataxia but an ataxia with somewhat different qualshyities (see Section on ldquoNeurologic Signs of Vestibular System Dysfunctionrdquo) General proprioception consists of two separate components one is the conscious proshyprioceptive pathway which involves the transmission of proprioceptive information to the cerebral cortex the other is for segmental reflex activity and transmitshyting proprioceptive information to the cerebellum Broadly conscious proprioception is the conscious awareness of body position and movement of body segments and monitoring of limb position while the animal is stationary In horses we assume that a deficit in replacing a limb in the correct position after for example spinning it in a circle is due to a deficit in conscious proprioception and is a component of an ataxic gait The subconscious system monitors proprioshyception when the animal is in motion and a deficit is likely to result in the ldquoswingingrdquo movements particushylarly of the pelvic limbs when an ataxic horse is turned sharply

General proprioception anatomyGeneral proprioceptive impulses from receptors in musshycles and joints are relayed to higher centers where they can reach a state of conscious perception (forebrain) or remain at a subconscious level (cerebellum) The pathshyways for proprioception are formed by a chain of neurons with synapses at specific levels of the nervous system For conscious proprioception there are three neurons in the chain while for subconscious proprioception there are only two neurons in the pathway

Conscious proprioceptionConscious proprioception is mediated by pathways in the dorsal column of the spinal cord through pathshyways that begin in joint receptors and end in the parietal lobe of the cerebral cortex it enables the cortex to refine voluntary movements The cell bodies of the neurons that are responsible for detecting proshyprioceptive changes are located in the dorsal root ganshyglia and the dendrites of these neurons are modified to function as proprioceptors The axons of the first‐order cells project as part of the dorsal root of the spinal nerve and enter the white matter of the dorsal

funiculus As these axons turn and pass cranially through the spinal cord they form the discrete fiber tract in the dorsal funiculus identified as the fascicshyulus gracilis medially when information arises from the pelvic limbs and in the more laterally placed fasshyciculus cuneatus for impulses from the thoracic limbs These fibers ascend ipsilaterally until they reach their site of synapse in the caudal medulla oblongata at the level with the obex at which point the axons in the fasciculus gracilis synapse with the bilateral gracilis nucleus and those in the fasciculus cuneatus synapse with the medial cuneate nucleus The neurons in this nucleus are the second‐order neurons in this conshyscious proprioceptive pathway As the second‐order axons cross the midline of the brainstem they form the deep arcuate fibers and they then move rostrally and ascend in the brainstem as a component of a fiber bundle known as the medial lemniscus The synapse with the third‐order neuron occurs in the thalamus These third‐order neurons send their axons ipsilatershyally through the internal capsule to their termination in the somesthetic cerebral cortex

Subconscious proprioceptionThe cell body of the first‐order neuron for subconscious proprioception is also in a spinal ganglion The second neurons however with the exception of the small cuneocerebellar tract are located not in the brainstem but in the dorsal horn of the spinal cord these neurons send their axons to the cerebellum via the lateral funiculi of the spinal cord The spinocerebellar tracts can be further subdivided into the dorsal and ventral spinoshycerebellar tracts carrying information from the pelvic limbs and the more medially placed cuneocerebellar and rostral spinocerebellar tracts which are related to information from the thoracic limbs This arrangement may be one of the reasons why spinal cord compressions invariably have more severe clinical signs in the pelvic limbs compared with the thoracic limb the pelvic limb tracts are more superficially placed and far more easily damaged Subconscious proprioceptive information is ultimately relayed to the cerebellar cortex by axons that enter the caudal cerebellar peduncle to synapse in the cerebellar cortex

NociceptionFibers carrying impulses related to touch and noxious stimuli form the spinothalamic tract as they ascend through the spinal cord ldquoTractrdquo is actually a misnomer as unlike in primates this is a diffuse network of axons deep in the spinal cord with numerous ipsilateral and contralateral interconnections compared Only a severe spinal cord lesion can damage this diffuse and multishysynaptic pathway to the extent that limb nociception (ldquodeep painrdquo) is lost


The first‐order neuron is again located in the spinal ganglion First‐order axons ascend and descend in the cord traversing short intersegmental distance prior to synapsing with neurons in the substantia gelatinosa a superficial gray matter layer of the spinal cord dorsal horn Second‐order axons immediately cross to the opposite side and form a diffuse spinothalamic tract in the contralateral funiculus At the level of the thalamus a synapse occurs on the third‐order neuron in thalamus Third‐order axons enter into the formation of the internal capsule as they travel to their respective site of synapse in the somesthetic cortex

Areas of innervation supplied by a single nerve are called an autonomous innervation zone and knowledge of their distribution can be useful when testing for peripheral nerve damage (for reference see Figure 334) Note that unlike humans and small animals equids do not have an autonomous zone for the radial nerve

The vestibular systemMany equine neurological patients present with clinical signs related to vestibular dysfunction most commonly a head tilt (see Figure 91) and clinicians need to be comfortable with this system The vestibular system is a special sensory system of the body that monitors posishytion rotation and movement of the head and subseshyquently adjusts body posture and eye position Sensory receptors for balance and equilibrium are principally located in the semicircular canals of the inner ear and supported by proprioceptive information from the rest of the body and in horses particularly the dorsal roots of cranial cervical vertebrae The visual system also has inputs into the vestibular nuclei Impulses from the inner ear in response to head movement travel to the brainstem along the vestibular portion of the vestibuloshycochlear nerve (CN VIII) and the majority of the vestibshyular axons synapse in the brainstem on four pairs of vestibular nuclei in the very rostral medulla oblongata In turn axons from the vestibular nuclei project to the cerebellum the brainstem nuclei that regulate the extraocular eye muscles and the spinal cord There is a very close connection between the vestibular nuclei and neurons in the cerebellum particularly the flocshyculonodular lobe This phylogenetically older part of the cerebellum is responsible for providing the sensorishymotor coordination necessary to maintain balance and equilibrium

Ascending projections from the vestibular nuclei pass rostrally through the brainstem to the motor nuclei of the extraocular eye muscles as the ascending limb of the medial longitudinal fasciculus Appropriate stimulation of the eye muscles in response to these vestibular impulses initiated by head movement produces conjugate eye movement and dysfunction results in ventral strashybismus (Figure 92) and spontaneous nystagmus

The major fiber projection from the vestibular nuclei that enters the spinal cord forms the lateral vestibulospishynal tract located in the ventrolateral funiculus of white matter as shown in Figure 112 while a smaller projecshytion travels through the spinal cord in the ventral funicshyulus adjacent to the ventral median fissure This smaller bundle forms the medial vestibulospinal tract also idenshytified as the descending limb of the medial longitudinal fasciculus the tract that in the brainstem transmits vesshytibular control over cranial nerve nuclei The two vesshytibulospinal tracts are responsible for regulating the extensor muscle tone necessary to maintain balance and posture This is an important clinical concept the vestibshyular system regulates ipsilateral antigravity tone Vestibulospinal tract adjustments help to coordinate the activity of the limbs and trunks in response to head movements detected through the vestibular receptors in the inner ear

Neurologic signs of vestibular system dysfunctionClassical vestibular signs include a head tilt staggershying (ldquovestibular ataxiardquo) circling and nystagmus The origin of the classical vestibular signs is anatomically interesting and can be explained by the unequal input into the vestibular nuclei and resulting loss of ipsilatshyeral antigravity tone For example if a horse has a lesion on the right inner ear then the vestibular nuclei would have unbalanced input with left‐side input being greater than the right The brain would interpret the unbalanced input as indicating that the head is turning to the left resulting in decreased ipsishylateral (ie right‐sided) antigravity tone and increased antigravity extensor tone on the left Thus the patient would tilt stagger and circle to the right Even if the horse is at rest the brain perceives the animal to be turning to the left due to the unbalanced input and thus the eyes make rapid jerky movements to the left before drifting back across the orbit again so‐called left‐sided nystagmus which with rare exceptions means that the lesion is on the opposite side of the vestibular system

Lesions in the vestibular system may arise in the periphery (which practically means in the inner ear of the petrous temporal bone) or occasionally they may arise centrally in the brainstem the vestibular portions of the cerebellum or the relevant tracts in the cranial spinal cord Thus vestibular disease is called peripheral or central respectively and it is critical that clinicians differentiate the two by looking for other signs that may be evident in a central lesion Broadly this could include general proprioceptive ataxia UMN paresis or involveshyment of cranial nerves other than cranial nerve VII (which can be damaged by both central and peripheral lesions) Certain discrete central lesions disrupting


cerebellar inhibition of vestibular nuclei can result in vestibular signs mimicking those from the opposite side however the other central deficits for example UMN paresis will indicate the correct side of the lesion Visual inputs also affect the vestibular nuclei and (carefully) blindfolding in a horse with a marginal lesion and no otherwise‐obvious vestibular signs can induce dramatic vestibular signs

Autonomic nervous system a two‐LMN systemThe autonomic nervous system differs from the somatic nervous system in that it is not under voluntary control and that the effectors are two LMNs one in the CNS and one in ganglia in the periphery Similar to the somatic system it has UMNs situated in the brain and consists of motor and sensory systems The autonomic sensory system is broadly similar to the somatic sensory system although it tends not to reach conshysciousness and it will not be discussed further here The autonomic nervous system is responsible for the regulation of the visceral functions of the body The classical representation of the autonomic system divides the system into two functional components the sympathetic and parasympathetic divisions of the autonomic system The key point to understanding the anatomic arrangement of autonomic innervation is the realization that the system is represented by a model composed of two neurons that synapse on each other prior to innervating a target structure The site of synapse occurs in ganglia either close to the CNS in the abdomen or pelvis or indeed within a specific organ (such as the numerous submucosal and myenshyteric plexus neurons within the large and small intestines) The targets of autonomic innervation are cardiac muscle smooth muscle and glands Sympathetic and parasympathetic innervation of the same structure is usually antagonistic The sympathetic nervous system prepares the body for the classic ldquofight‐or‐flightrdquo response Parasympathetic innervation promotes ldquorest and recoveryrdquo functions of the body

Sympathetic nervous systemSympathetic innervation is provided through a chained network of two neurons that synapse on each other in a ganglion prior to reaching the target of innervation The first neuron in this chain is identified as the presynaptic neuron of origin for the sympathetic system The presynaptic soma is located in the lateral horn of the thoracic and lumbar segments of the spinal cord For this reason it is frequently called the thorashycolumbar division of the autonomic nervous system The presynaptic nerve fiber that is the axon of the

presynaptic soma leaves the spinal cord to synapse on the second neuron in the chain identified as the postsynaptic soma

The sympathetic postsynaptic soma is located in one of the ganglia of the sympathetic division of the system where it receives the synaptic contact of the presynshyaptic fiber Sympathetic ganglia can be classified into two main groups either paravertebral (parallel to the vertebral column) or prevertebral (some distance from the CNS) ganglia A third group of sympathetic ganglia are found embedded in the organ to be innervated

Prevertebral sympathetic ganglia are positioned approximately along the midline ventral to the vertebral column They are wrapped around the origins of the major abdominal blood vessels that come from the aorta The prevertebral ganglia are the celiacomesenshyteric ganglion and the caudal mesenteric ganglion It is within these ganglia that the presynaptic axon synapses on the postsynaptic soma In turn the postsynaptic synaptic sends its axon into the periphery to reach the target of innervation

The other main site of synapse for presynaptic sympathetic cells is in the paravertebral ganglia These ganglia are located more laterally in relation to the position of the vertebral column The paravertebral sympathetic ganglia are the cervical ganglia in the neck and the segshymentally distributed ganglia along the sympathetic chain in the thoracic and abdominal cavities

There are two pairs of cervical ganglia closely assoshyciated with the vagosympathetic trunk as it traverses the neck The cranial cervical ganglia are located in the wall of the guttural pouch and British patholoshygists have become adept at finding these as they are the principal biopsy site for the diagnosis of equine dysautonomia (grass sickness) The middle cervical ganglia are located near the thoracic inlet In the species of major veterinary interest the caudal cervical ganglion has fused with the most cranial ganglion of the sympathetic chain at the level of the first rib This conjoined structure is identified as the cervicothoracic ganglion

Due to the varying distribution of sympathetic ganshyglia the presynaptic fibers can take several paths as they travel toward their ganglionic site of synapse with the second neuron in the chain (Figure 116) The third category of sympathetic ganglia is a miscellany of ganglia that are scattered along the aorta or are located near other organs These ganglia can be identified indishyvidually as aortic ganglia renal ganglia and adrenal ganglia

In the case of target structures in the head receiving sympathetic innervation this becomes a relatively

Equine Neurology




Leesburg USA


Lexington USA










2015007228





1 2015

v

Contents


Preface ix

































vi Contents











Index 488

vii

Contributors List



Davis USA



Baton Rouge USA


Western University

Pomona USA



Baton Rouge USA


Cornell University

Ithaca USA



Medicine

Leesburg USA


Lexington USA



Munich Germany



Midlothian UK


Gloucestershire UK



Knoxville USA


Cornell University

Ithaca USA



Lexington USA



Kennett Square USA


Massey University




Stillwater USA



Gainesville USA



Gainesville USA




Columbus USA



Fort Collins USA


Derby UK


Lexington USA



Medicine

Leesburg USA






Baton Rouge USA



Columbus USA



Columbus USA



Gainesville USA

ix

Preface





x






Section 1


3









Development












(a)

1

2

3

4

5

(b)

(c)

(d)


1

2

3

4

5

6

7

(a) (b)






1

3

4

5

6

7

2




Sensory


Optic CN II Vision


Motor







Mixed



lacrimation








1

2

3


1

106

7

14

8

15

1112

16

13

9

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4

5

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1

2

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8

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10

11

12

13

14

15

16

1718

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27

28

29

19

20

21

22

23

24







10 11 12 13

14

1516171819

4321

5

6 89

7


1

2

3

4

5

6

7

8

12

13

1415

16

17

18

19

9

1011

IV



















987

6

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(a)

12

3

45

6

7

(b)

1

2

34 5

678

9101112

13































Leesburg USA


Lexington USA










2015007228





1 2015

v

Contents


Preface ix

































vi Contents











Index 488

vii

Contributors List



Davis USA



Baton Rouge USA


Western University

Pomona USA



Baton Rouge USA


Cornell University

Ithaca USA



Medicine

Leesburg USA


Lexington USA



Munich Germany



Midlothian UK


Gloucestershire UK



Knoxville USA


Cornell University

Ithaca USA



Lexington USA



Kennett Square USA


Massey University




Stillwater USA



Gainesville USA



Gainesville USA




Columbus USA



Fort Collins USA


Derby UK


Lexington USA



Medicine

Leesburg USA






Baton Rouge USA



Columbus USA



Columbus USA



Gainesville USA

ix

Preface





x






Section 1


3









Development












(a)

1

2

3

4

5

(b)

(c)

(d)


1

2

3

4

5

6

7

(a) (b)






1

3

4

5

6

7

2




Sensory


Optic CN II Vision


Motor







Mixed



lacrimation








1

2

3


1

106

7

14

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1112

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13

9

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4

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11

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13

14

15

16

1718

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27

28

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19

20

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23

24







10 11 12 13

14

1516171819

4321

5

6 89

7


1

2

3

4

5

6

7

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12

13

1415

16

17

18

19

9

1011

IV



















987

6

1 3

45

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1 2345


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4





















13

12

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(a)

12

3

45

6

7

(b)

1

2

34 5

678

9101112

13





































2015007228





1 2015

v

Contents


Preface ix

































vi Contents











Index 488

vii

Contributors List



Davis USA



Baton Rouge USA


Western University

Pomona USA



Baton Rouge USA


Cornell University

Ithaca USA



Medicine

Leesburg USA


Lexington USA



Munich Germany



Midlothian UK


Gloucestershire UK



Knoxville USA


Cornell University

Ithaca USA



Lexington USA



Kennett Square USA


Massey University




Stillwater USA



Gainesville USA



Gainesville USA




Columbus USA



Fort Collins USA


Derby UK


Lexington USA



Medicine

Leesburg USA






Baton Rouge USA



Columbus USA



Columbus USA



Gainesville USA

ix

Preface





x






Section 1


3









Development












(a)

1

2

3

4

5

(b)

(c)

(d)


1

2

3

4

5

6

7

(a) (b)






1

3

4

5

6

7

2




Sensory


Optic CN II Vision


Motor







Mixed



lacrimation








1

2

3


1

106

7

14

8

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1112

16

13

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2

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10 11 12 13

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4321

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18

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1011

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987

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(a)

12

3

45

6

7

(b)

1

2

34 5

678

9101112

13




























v

Contents


Preface ix

































vi Contents











Index 488

vii

Contributors List



Davis USA



Baton Rouge USA


Western University

Pomona USA



Baton Rouge USA


Cornell University

Ithaca USA



Medicine

Leesburg USA


Lexington USA



Munich Germany



Midlothian UK


Gloucestershire UK



Knoxville USA


Cornell University

Ithaca USA



Lexington USA



Kennett Square USA


Massey University




Stillwater USA



Gainesville USA



Gainesville USA




Columbus USA



Fort Collins USA


Derby UK


Lexington USA



Medicine

Leesburg USA






Baton Rouge USA



Columbus USA



Columbus USA



Gainesville USA

ix

Preface





x






Section 1


3









Development












(a)

1

2

3

4

5

(b)

(c)

(d)


1

2

3

4

5

6

7

(a) (b)






1

3

4

5

6

7

2




Sensory


Optic CN II Vision


Motor







Mixed



lacrimation








1

2

3


1

106

7

14

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9

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4

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29

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24







10 11 12 13

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1516171819

4321

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2

3

4

5

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1415

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17

18

19

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1011

IV



















987

6

1 3

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2

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1 2345


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13

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(a)

12

3

45

6

7

(b)

1

2

34 5

678

9101112

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vi Contents











Index 488

vii

Contributors List



Davis USA



Baton Rouge USA


Western University

Pomona USA



Baton Rouge USA


Cornell University

Ithaca USA



Medicine

Leesburg USA


Lexington USA



Munich Germany



Midlothian UK


Gloucestershire UK



Knoxville USA


Cornell University

Ithaca USA



Lexington USA



Kennett Square USA


Massey University




Stillwater USA



Gainesville USA



Gainesville USA




Columbus USA



Fort Collins USA


Derby UK


Lexington USA



Medicine

Leesburg USA






Baton Rouge USA



Columbus USA



Columbus USA



Gainesville USA

ix

Preface





x






Section 1


3









Development












(a)

1

2

3

4

5

(b)

(c)

(d)


1

2

3

4

5

6

7

(a) (b)






1

3

4

5

6

7

2




Sensory


Optic CN II Vision


Motor







Mixed



lacrimation








1

2

3


1

106

7

14

8

15

1112

16

13

9

2

4

5

3










1

2

3

4

5

6


1

2

34

5

6

7

25

8

9

10

11

12

13

14

15

16

1718

26

27

28

29

19

20

21

22

23

24







10 11 12 13

14

1516171819

4321

5

6 89

7


1

2

3

4

5

6

7

8

12

13

1415

16

17

18

19

9

1011

IV



















987

6

1 3

45

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2

(a)

(b)

1 2345


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10

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4





















13

12

11

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1415

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65

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2

3

4 5

6




















(a)

12

3

45

6

7

(b)

1

2

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678

9101112

13




























vii

Contributors List



Davis USA



Baton Rouge USA


Western University

Pomona USA



Baton Rouge USA


Cornell University

Ithaca USA



Medicine

Leesburg USA


Lexington USA



Munich Germany



Midlothian UK


Gloucestershire UK



Knoxville USA


Cornell University

Ithaca USA



Lexington USA



Kennett Square USA


Massey University




Stillwater USA



Gainesville USA



Gainesville USA




Columbus USA



Fort Collins USA


Derby UK


Lexington USA



Medicine

Leesburg USA






Baton Rouge USA



Columbus USA



Columbus USA



Gainesville USA

ix

Preface





x






Section 1


3









Development












(a)

1

2

3

4

5

(b)

(c)

(d)


1

2

3

4

5

6

7

(a) (b)






1

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6

7

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Sensory


Optic CN II Vision


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1

2

3


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10 11 12 13

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(a)

12

3

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(b)

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9101112

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Columbus USA



Fort Collins USA


Derby UK


Lexington USA



Medicine

Leesburg USA






Baton Rouge USA



Columbus USA



Columbus USA



Gainesville USA

ix

Preface





x






Section 1


3









Development












(a)

1

2

3

4

5

(b)

(c)

(d)


1

2

3

4

5

6

7

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10 11 12 13

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(a)

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ix

Preface





x






Section 1


3









Development












(a)

1

2

3

4

5

(b)

(c)

(d)


1

2

3

4

5

6

7

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3

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6

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Sensory


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2

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8

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10 11 12 13

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Section 1


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6

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10

9

7

3

4





















13

12

11

10

1415

8

65

4

3

2

9


1 23

4

5

6

78

9

10

11









1

2

3

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6




















(a)

12

3

45

6

7

(b)

1

2

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678

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3









Development












(a)

1

2

3

4

5

(b)

(c)

(d)


1

2

3

4

5

6

7

(a) (b)






1

3

4

5

6

7

2




Sensory


Optic CN II Vision


Motor







Mixed



lacrimation








1

2

3


1

106

7

14

8

15

1112

16

13

9

2

4

5

3










1

2

3

4

5

6


1

2

34

5

6

7

25

8

9

10

11

12

13

14

15

16

1718

26

27

28

29

19

20

21

22

23

24







10 11 12 13

14

1516171819

4321

5

6 89

7


1

2

3

4

5

6

7

8

12

13

1415

16

17

18

19

9

1011

IV



















987

6

1 3

45

6

2

(a)

(b)

1 2345


12

5

6

8

10

9

7

3

4





















13

12

11

10

1415

8

65

4

3

2

9


1 23

4

5

6

78

9

10

11









1

2

3

4 5

6




















(a)

12

3

45

6

7

(b)

1

2

34 5

678

9101112

13


































(a)

1

2

3

4

5

(b)

(c)

(d)


1

2

3

4

5

6

7

(a) (b)






1

3

4

5

6

7

2




Sensory


Optic CN II Vision


Motor







Mixed



lacrimation








1

2

3


1

106

7

14

8

15

1112

16

13

9

2

4

5

3










1

2

3

4

5

6


1

2

34

5

6

7

25

8

9

10

11

12

13

14

15

16

1718

26

27

28

29

19

20

21

22

23

24







10 11 12 13

14

1516171819

4321

5

6 89

7


1

2

3

4

5

6

7

8

12

13

1415

16

17

18

19

9

1011

IV



















987

6

1 3

45

6

2

(a)

(b)

1 2345


12

5

6

8

10

9

7

3

4





















13

12

11

10

1415

8

65

4

3

2

9


1 23

4

5

6

78

9

10

11









1

2

3

4 5

6




















(a)

12

3

45

6

7

(b)

1

2

34 5

678

9101112

13
































1

3

4

5

6

7

2




Sensory


Optic CN II Vision


Motor







Mixed



lacrimation








1

2

3


1

106

7

14

8

15

1112

16

13

9

2

4

5

3










1

2

3

4

5

6


1

2

34

5

6

7

25

8

9

10

11

12

13

14

15

16

1718

26

27

28

29

19

20

21

22

23

24







10 11 12 13

14

1516171819

4321

5

6 89

7


1

2

3

4

5

6

7

8

12

13

1415

16

17

18

19

9

1011

IV



















987

6

1 3

45

6

2

(a)

(b)

1 2345


12

5

6

8

10

9

7

3

4





















13

12

11

10

1415

8

65

4

3

2

9


1 23

4

5

6

78

9

10

11









1

2

3

4 5

6




















(a)

12

3

45

6

7

(b)

1

2

34 5

678

9101112

13

































1

2

3


1

106

7

14

8

15

1112

16

13

9

2

4

5

3










1

2

3

4

5

6


1

2

34

5

6

7

25

8

9

10

11

12

13

14

15

16

1718

26

27

28

29

19

20

21

22

23

24







10 11 12 13

14

1516171819

4321

5

6 89

7


1

2

3

4

5

6

7

8

12

13

1415

16

17

18

19

9

1011

IV



















987

6

1 3

45

6

2

(a)

(b)

1 2345


12

5

6

8

10

9

7

3

4





















13

12

11

10

1415

8

65

4

3

2

9


1 23

4

5

6

78

9

10

11









1

2

3

4 5

6




















(a)

12

3

45

6

7

(b)

1

2

34 5

678

9101112

13




































1

2

3

4

5

6


1

2

34

5

6

7

25

8

9

10

11

12

13

14

15

16

1718

26

27

28

29

19

20

21

22

23

24







10 11 12 13

14

1516171819

4321

5

6 89

7


1

2

3

4

5

6

7

8

12

13

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16

17

18

19

9

1011

IV



















987

6

1 3

45

6

2

(a)

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12

5

6

8

10

9

7

3

4





















13

12

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1415

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9


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5

6

78

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10

11









1

2

3

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6




















(a)

12

3

45

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7

(b)

1

2

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678

9101112

13

































10 11 12 13

14

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4321

5

6 89

7


1

2

3

4

5

6

7

8

12

13

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16

17

18

19

9

1011

IV



















987

6

1 3

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(a)

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12

5

6

8

10

9

7

3

4





















13

12

11

10

1415

8

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4

3

2

9


1 23

4

5

6

78

9

10

11









1

2

3

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6




















(a)

12

3

45

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7

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1

2

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9101112

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987

6

1 3

45

6

2

(a)

(b)

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12

5

6

8

10

9

7

3

4





















13

12

11

10

1415

8

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4

3

2

9


1 23

4

5

6

78

9

10

11









1

2

3

4 5

6




















(a)

12

3

45

6

7

(b)

1

2

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9101112

13
































987

6

1 3

45

6

2

(a)

(b)

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12

5

6

8

10

9

7

3

4





















13

12

11

10

1415

8

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4

3

2

9


1 23

4

5

6

78

9

10

11









1

2

3

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6




















(a)

12

3

45

6

7

(b)

1

2

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9101112

13















































13

12

11

10

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8

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4

3

2

9


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5

6

78

9

10

11









1

2

3

4 5

6




















(a)

12

3

45

6

7

(b)

1

2

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678

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13





































13

12

11

10

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9


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5

6

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9

10

11









1

2

3

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6




















(a)

12

3

45

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(b)

1

2

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678

9101112

13



































1

2

3

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6




















(a)

12

3

45

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(b)

1

2

34 5

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13














































(a)

12

3

45

6

7

(b)

1

2

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678

9101112

13


































(a)

12

3

45

6

7

(b)

1

2

34 5

678

9101112

13




















































































Documents

Thumbnail - download.e-bookshelf.de · 2. Nervous system–Diseases. 3. Veterinary neurology. I. Furr, Martin, editor. II. Reed, Stephen M., editor. [DNLM: 1. Central Nervous System