King’s Applied Anatomy of  the Central Nervous System of Domestic Mammals

King’s Applied Anatomy of the Central Nervous System of Domestic Mammals

Geoff Skerritt, BVSc, FRSB, CBiol, DipECVN, FRCVS

Royal College of Veterinary Surgeons Specialist and European Specialist in Veterinary Neurology Chester, UK

Second Edition

This second edition first published 2018© 2018 John Wiley & Sons Ltd

Edition History: Oxford University Press (1e, 1987)

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Set in 10/12pt Warnock by SPi Global, Pondicherry, India

10 9 8 7 6 5 4 3 2 1

I wish to dedicate this second edition of Tony King’s book on the central nervous system of the domestic animals.

Firstly, to Tony King himself, a brilliant teacher and author. I am sorry that Tony died before he was able to make any contribution to the second edition of this book, but he would have been delighted to know that it has been updated and re‐published.

Secondly, it is with great sadness that my friend and colleague, Ulrike Michal, died before she was able to contribute to the book. She was a very competent clinician and a natural academic. Ulrike’s artwork and knowledge would have enhanced the book, but I hope she would have been pleased with the end result anyhow!

vii

Foreword xvii Preface xix Acknowledgement xxi About the Contributors xxiii About the Companion Website xxv

1 Arterial Supply to the Central Nervous System 1 Arterial Supply to the Brain 11.1 Basic Pattern of the Main Arteries Supplying the Brain 11.2 Basic Pattern of Incoming Branches to the Cerebral Arterial Circle 11.3 Species Variations 21.4 Summary of the Significance of the Vertebral Artery as a Source

of Blood to the Brain 51.5 Humane Slaughter 61.6 Rete Mirabile 7 Superficial Arteries of the Spinal Cord 81.7 Main Trunks 81.8 Anastomosing Arteries 81.9 Segmental Arteries to the Spinal Cord 101.10 General Principles Governing the Distribution of Arteries below

the Surface of the Neuraxis 101.11 The Deep Arteries of the Spinal Cord 101.12 The Problem of Pulsation 111.13 Arterial Anastomoses of the Neuraxis 11

2 The Meninges and Cerebrospinal Fluid 13 Meninges 132.1 General Anatomy of the Cranial and Spinal Meninges 132.2 Anatomy of the Meninges at the Roots of Spinal and Cranial Nerves 142.3 The Spaces around the Meninges 142.4 Relationship of Blood Vessels to the Meninges 162.5 The Filum Terminale 162.6 The Falx Cerebri and Membranous Tentorium Cerebelli 16 Cerebrospinal Fluid 162.7 Formation of Cerebrospinal Fluid 162.8 The Choroid Plexuses 16

Contents

Contentsviii

2.9 Mechanism of Formation of Cerebrospinal Fluid 172.10 Circulation of Cerebrospinal Fluid 172.11 Drainage of Cerebrospinal Fluid 192.12 Functions of Cerebrospinal Fluid 202.13 Blood‐brain Barrier 212.14 Collection of Cerebrospinal Fluid 222.15 Clinical Conditions of the Cerebrospinal Fluid System 23

3 Venous Drainage of the Spinal Cord and Brain 25 The Cranial System of Venous Sinuses 253.1 General Plan 253.2 The Components of the Dorsal System of Sinuses 273.3 The Components of the Ventral System of Sinuses 283.4 Drainage of the Cranial Sinuses into the Systemic Circulation 28 The Spinal System of Venous Sinuses 293.5 General Plan 293.6 Connections to the Cranial System of Sinuses 293.7 Territory Drained by the Spinal System of Sinuses 293.8 Drainage of the Spinal Sinuses into the Systemic Circulation 29 Clinical Significance of the Venous Drainage of the Neuraxis 303.9 Spread of Infection in the Head 303.10 Paradoxical Embolism 303.11 Venous Obstruction 303.12 Angiography for Diagnosis 31

4 The Applied Anatomy of the Vertebral Canal 33 The Anatomy of Epidural Anaesthesia and Lumbar Puncture 334.1 The Vertebrae 334.2 Spinal Cord 334.3 Meninges 354.4 Lumbar Puncture 354.5 Epidural Anaesthesia in the Ox 354.6 Injuries to the Root of the Tail 36 The Anatomy of the Intervertebral Disc 364.7 The Components of the Disc 364.8 Senile Changes 384.9 Disc Protrusion 384.10 Fibrocartilaginous Embolism 41 Malformation or Malarticulation of Vertebrae 414.11 The ‘Wobbler Syndrome’ in the Dog 414.12 The Wobbler Syndrome in the Horse 414.13 Atlanto‐Axial Subluxation in Dogs 424.14 Anomalous Atlanto‐Occipital Region in Arab Horses 424.15 Other Vertebral Abnormalities in Dogs 42

5 The Neuron 43 The Anatomy of Neurons 435.1 General Structure 43

Contents ix

5.2 The Axon 465.3 Epineurium, Perineurium and Endoneurium 505.4 The Synapse 515.5 Phylogenetically Primitive and Advanced Neurons 545.6 Axonal Degeneration and Regeneration in Peripheral Nerves 555.7 Regeneration and Plasticity in the Neuraxis 585.8 Stem Cells and Olfactory Ensheathing Cells 585.9 The Reflex Arc 595.10 Decussation: The Coiling Reflex 60

6 The Nerve Impulse 63 Excitation and Inhibition 636.1 Ion Channels and Gating Mechanisms 636.2 The Membrane Potential 646.3 The Excitatory Postsynaptic Potential 646.4 The Inhibitory Postsynaptic Potential 676.5 The Receptor Potential 686.6 The End‐plate Potential 696.7 Summary of Decremental Potentials 706.8 The Action Potential 716.9 Concerning Water Closets 736.10 Transducer Mechanisms of Receptors 736.11 Astrocytes 766.12 Oligodendrocytes 766.13 Microglia 77

7 Nuclei of the Cranial Nerves 79 General Principles Governing the Architecture of the 

Nuclei of the Cranial Nerves 797.1 Shape and Position of the Central Canal 797.2 Fragmentation of the Basic Columns of Grey Matter 797.3 Development of an Additional Component; Special Visceral Efferent 807.4 The Cranial Nerves of the Special Senses 827.5 Summary of the Architectural Principles of the Nuclei of 

the Cranial Nerves 82 Names, Topography and Functions of the Cranial Nerve Nuclei 827.6 Somatic Afferent Nucleus 827.7 Visceral Afferent Nucleus 857.8 Visceral Efferent Nuclei 857.9 Special Visceral Efferent Nuclei 867.10 Somatic Efferent Nuclei 86 Reflex Arcs of the Nuclei of the Cranial Nerves 87 Significance of the Nuclei of the Cranial Nerves in Clinical Neurology 88

8 Medial Lemniscal System 89 Conscious Sensory Modalities, their Receptors and Pathways 898.1 Conscious Sensory Modalities 898.2 Peripheral Receptors of Touch, Pressure and Joint Proprioception 91

Contentsx

8.3 Pathways of Touch, Pressure and Joint Proprioception 92 Clinical Conditions Affecting the Medial Lemniscal System 948.4 Effects of Lesions in the Dorsal Funiculus 94 Pain Pathways 968.5 Peripheral Receptors of Pain 968.6 Spinothalamic Tract of Man 978.7 Spinothalamic Pathways in Domestic Mammals 1008.8 Spinocervical Tract (Spinocervicothalamic Tract) 1008.9 Species Variations in the Medial Lemniscal System 1008.10 Somatotopic Localisation 1018.11 Blending of Tracts in the Spinal Cord 1018.12 Summary of the Medial Lemniscus System 101

9 The Special Senses 103 Vision 1039.1 Neuron 1 1039.2 Neuron 2 1039.3 Neuron 3 103 Hearing 1069.4 Neuron 1 1069.5 Neuron 2 1069.6 Neuron 3 106 Balance 1079.7 Neuron 1 1079.8 Neuron 2 107 Taste 1129.9 Neuron 1 1129.10 Neuron 2 1129.11 Neuron 3 112 Olfaction Proper: The Sense of Smell 1139.12 Neuron 1 1139.13 Neuron 2 1149.14 Neuron 3 114 Summary of the Conscious Sensory Systems 117

10 Spinocerebellar Pathways and Ascending Reticular Formation 11910.1 Spinocerebellar Pathways 11910.2 Ascending Reticular Formation 119 Spinocerebellar Pathways 12010.3 Hindlimbs 12010.4 Forelimbs 12210.5 Projections of Spinocerebellar Pathways to the Cerebral Cortex 12310.6 Functions of the Spinocerebellar Pathways 12410.7 Species Variations 124 Ascending Reticular Formation 12410.8 Organisation 124

Contents xi

Functions of the Ascending Reticular Formation 12810.9 Arousal 12810.10 Transmission of Deep Pain 12810.11 Summary of Spinocerebellar Pathways and Ascending Reticular

Formation 132

11 Somatic Motor Systems 135 Somatic Efferent Neurons 13511.1 Motor Neurons in the Ventral Horn of the Spinal Cord 135 Muscle Spindles 13711.2 Structure of the Muscle Spindle 13711.3 The Mode of Operation of the Muscle Spindle 13711.4 Role of Muscle Spindles in Posture and Movement 13911.5 Golgi Tendon Organs 13911.6 Muscle Tone 14011.7 Motor Unit 14111.8 Recruitment of Motor Units 14111.9 Summary of Ways of Increasing the Force of Contraction of a Muscle 142 The Final Common Path 14211.10 Algebraic Summation at the Final Common Path 14211.11 Renshaw Cells 14211.12 Lower Motor Neuron 14211.13 Integration of the Two Sides of the Neuraxis 143

12 Pyramidal System 145 Pyramidal Pathways 14512.1 The Neuron Relay 145 Feedback Pathways of the Pyramidal System 14812.2 Feedback of the Pyramidal System 148 Comparative Anatomy of the Pyramidal System 14912.3 Species Variations in the Primary Motor Area of the

Cerebral Cortex 14912.4 Species Variations in the Pyramidal System 15012.5 The Function of the Pyramidal System 150 Clinical Considerations 15112.6 Effects of Lesions in the Pyramidal System 15112.7 Validity of the Distinction between Pyramidal and 

Extrapyramidal Systems 152

13 Extrapyramidal System 153 Motor Centres 15313.1 Nine Command Centres 15313.2 The Cerebral Cortex 15313.3 Basal Nuclei and Corpus Striatum 15413.4 Midbrain Reticular Formation 15513.5 Red Nucleus 155

Contentsxii

13.6 Mesencephalic Tectum 15513.7 Pontine Motor Reticular Centres 15613.8 Lateral Medullary Motor Reticular Centres 15613.9 Medial Medullary Motor Reticular Centres 15613.10 Vestibular Nuclei 156 Spinal Pathways 15613.11 Pontine and Medullary Reticulospinal Tracts 15613.12 Rubrospinal Tract 15813.13 Vestibulospinal Tract 15913.14 Tectospinal Tract 15913.15 The Position in the Spinal Cord of the Tracts of 

the Extrapyramidal System 15913.16 Summary of the Tracts of the Extrapyramidal System 159

14 Extrapyramidal Feedback and Upper Motor Neuron Disorders 161 Feedback of the Extrapyramidal System 16114.1 Neuronal Centres of the Feedback Circuits 16114.2 Feedback Circuits 16114.3 Balance between Inhibitory and Facilitatory Centres 16414.4 Clinical Signs of Lesions in Extrapyramidal Motor Centres in Man 16514.5 Clinical Signs of Lesions in the Basal Nuclei in Domestic Animals 16614.6 Upper Motor Neuron Disorders 166

15 Summary of the Somatic Motor Systems 169 The Motor Components of the Neuraxis 16915.1 Pyramidal System 16915.2 Extrapyramidal System 17015.3 Distinction between Pyramidal and Extrapyramidal Systems 171 Clinical Signs of Motor System Injuries 17115.4 Functions of the Pyramidal and Extrapyramidal Systems:

Effects of Injury to the Motor Command Centres 17115.5 Upper Motor Neuron 17115.6 Lower Motor Neuron 17215.7 Summary of Projections onto the Final Common Path 173

16 The Cerebellum 175 Afferent Pathways to the Cerebellum 17516.1 Ascending from the Spinal Cord 17516.2 Feedback Input into the Cerebellar Cortex 175 Arterial Supply to the Brain 177 Summary of Pathways in the Cerebellar Peduncles 17816.3 Caudal Cerebellar Peduncle 17916.4 Middle Cerebellar Peduncle 17916.5 Rostral Cerebellar Peduncle 179 Rostral Cerebellar Peduncle 17916.6 Vestibular Areas 17916.7 Proprioceptive Areas 179

Contents xiii

16.8 Feedback Areas 180 Functions of the Cerebellum 18016.9 Co‐ordination and Regulation of Movement 18016.10 Control of Posture 18116.11 Ipsilateral Function of the Cerebellum 18116.12 Summary of Cerebellar Function 18116.13 Functional Histology of the Cerebellum 182 Clinical Conditions of the Cerebellum 18416.14 The Three Cerebellar Syndromes 18416.15 Cerebellar Disease in Domestic Mammals and Man 185

17 Autonomic Components of the Central Nervous System 187 Neocortex and Hippocampus 18717.1 Cortical Components 18717.2 Hippocampus 188 Diencephalon 18817.3 Hypothalamus 188 The Autonomic Functions of the Hypothalamus 19017.4 Amygdaloid Body and Septal Nuclei 19217.5 Habenular Nuclei 19317.6 Hindbrain Autonomic Areas 193 The Autonomic Areas of the Hindbrain 19317.7 Autonomic Motor Pathways in the Spinal Cord 19417.8 Ascending (Afferent) Visceral Pathways in the Spinal Cord

and Brainstem 195 Clinical Disorders of the Autonomic System 19517.9 Effects of Lesions in Autonomic Pathways 19517.10 Summary of Descending Autonomic Pathways 197

18 The Cerebral Cortex and Thalamus 199 Cerebral Cortex 19918.1 Projection Areas and Association Areas 19918.2 Instinct 20018.3 Cerebral Cortex in Primitive Mammals 20018.4 Cerebral Cortex in the Cat and Dog 20018.5 Conditioned Reflexes 20018.6 Cerebral Cortex in Man 20118.7 Cognitive Association Area in Man 20218.8 Cognitive Association Area in Carnivores 20318.9 Interpretative Association Area in Man 20418.10 Interpretative Association Area in Carnivores 20418.11 Frontal Association Area in Man 20418.12 Frontal Association Area in Carnivores 20518.13 Corpus Callosum 205 Clinical Conditions of the Cerebral Cortex 20518.14 Effects of Extensive Damage to the Cerebral Hemisphere in Domestic

Mammals 205

Contentsxiv

18.15 Seizures 207 Histology of the Cerebral Cortex 20818.16 Histology of the Cerebral Cortex 208 Thalamus 20818.17 Ventral Group of Thalamic Nuclei 20918.18 The Lateral Group 21018.19 Central (or Intralaminar) Group 21018.20 Dorsomedial Group 21018.21 Summary of Incoming Afferent Paths to the Thalamus: 21018.22 Summary of the Projections from the Thalamus to the Cerebral Cortex 21118.23 Summary of Functions of the Thalamus: 21118.24 Clinical Effects of Lesions of the Thalamus in Domestic Mammals 21218.25 Clinical Effects of Lesions of the Thalamus in Man 212 Growth of the Human Brain 212

19 Embryological and Comparative Neuroanatomy 215 The Embryological Development of the Central Nervous System 21519.1 The Development of the Brain 21519.2 The Development of the Spinal Cord 21719.3 The Development of the Neural Crest 217 Evolution of the Vertebrate Forebrain 21819.4 Primitive Vertebrates 21819.5 Contemporary Amphibian 21819.6 Contemporary Advanced Reptile 21919.7 Mammal 22019.8 Bird 22119.9 Major Homologies in Mammals and Birds 222 Evolution of the Capacity to Differentiate Sensory Modalities 22319.10 Lower Vertebrates, Including Amphibians 22319.11 Advanced Reptiles and Birds 22319.12 Mammals 223 Special Features of the Avian Brain 22319.13 Size of the Brain 22319.14 Poor Development of the Cerebral Cortex 22319.15 External Striatum 22419.16 Colliculi: The Optic Lobe 22419.17 Olfactory Areas 22419.18 Cerebellum 22519.19 Spinocerebellar Pathways 22619.20 Cuneate and Gracile Fascicles 22619.21 Motor Spinal Pathways 227

20 Clinical Neurology 22920.1 Mental Status 22920.2 Posture 23020.3 Gait 23020.4 Examination of the Cranial Nerves: Tests and Observations 232

Contents xv

Testing Postural and Locomotor Responses 24320.5 Tonic Neck and Eye Responses 24320.6 Proprioceptive Positioning Responses 24320.7 Placing Responses 24420.8 Extensor Postural Thrust 24520.9 Hopping 24520.10 Wheelbarrow Test 24520.11 Hemiwalking 24620.12 Righting 24720.13 Blindfolding 24720.14 Circling Test 24720.15 Sway Test 247 Examination of Spinal Reflexes 24720.16 Withdrawal (Flexor) Reflex 24720.17 Patellar Tendon Reflex 24920.18 Triceps Tendon Reflex 25020.19 Biceps Tendon Reflex 25020.20 Cutaneous Trunci/Colli (Formerly Panniculus) Reflex 25020.21 Perineal Reflex 25120.22 Crossed Extensor Reflex 25120.23 Babinski Reflex 251 Other Tests 25220.24 Assessment of Muscle Tone 25220.25 Testing Conscious Pain Responses 25220.26 Detecting Discomfort 25220.27 Testing the Sympathetic System 25220.28 Case Sheet 254

21 Imaging Techniques for Study of the Central Nervous System 257 General Considerations 25721.1 Species 25721.2 Objectives of Imaging in Clinical Neurology 25721.3 Computed Tomography and Magnetic Resonance Imaging 25821.4 The Use of Contrast Agents in Imaging 260 Intracranial Structures 26221.5 Positioning of the Head 26221.6 Breed and Age Variation in Images of the Head 262 Vertebral Column 26321.7 Positioning of the Patient 26321.8 Imaging the Vertebral Column 26421.9 Contrast Radiography of the Vertebral Column 267

22 Topographical Anatomy of the Central Nervous System 269 Spinal Cord 26922.1 Regions of the Spinal Cord 26922.2 Segments of Spinal Cord and their Relationship to Vertebrae 27022.3 General Organisation of Grey and White Matter 270

Contentsxvi

22.4 Dorsal, Lateral and Ventral Horns of Grey Matter 27122.5 Laminae of Grey Matter 27222.6 Funiculi of White Matter 27222.7 Tracts of the White Matter 273 Medulla Oblongata 27422.8 Gross Structure 27422.9 Cranial Nerves 27422.10 Ventricular System 27522.11 Internal Structure 277 Pons 28022.12 Gross Structure 28022.13 Cranial Nerves 28022.14 Ventricular System 28122.15 Internal Structure 281 Midbrain 28322.16 Gross Structure 28322.17 Cranial Nerves 28322.18 Ventricular System 28422.19 Internal Structure 284 Diencephalon 28822.20 Gross Structure 28822.21 Cranial Nerves 28922.22 Ventricular System 28922.23 Internal Structure 290 Cerebellum 29322.24 Gross Structure 29322.25 Internal Structure 29322.26 Cerebellar Peduncles 294 Cerebral Hemispheres 29522.27 Gross Structure 29522.28 Ventricular System 29622.29 Internal Structure 297

23 Electrodiagnostics 30323.1 Introduction 30323.2 Electromyography 30323.3 Nerve Conduction Velocity 30423.4 Electroencephalography 30423.5 Evoked Potentials 30523.6 Electroretinography 30723.7 Intra‐operative Monitoring of Spinal Cord Function 307

24 Diagnostic Exercises 30924.1 Introduction 30924.2 Solutions to Diagnostic Exercises 317

Appendix 325Further Reading 335Index 347

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When Tony King published the first edition of this textbook, it was a revelation for veterinary students to find functional neuroanatomy explained so straightforwardly and in a format easily searched when a specific question arose. For the past 30 years, neuroanatomy has changed little, but the way clinicians use applied neuroanatomy to interpret the results of new imaging techniques has revolutionised. Geoff Skerritt has updated the second edition to maintain Tony King’s clarity of explanation and has expanded it, especially with the results of new imaging techniques. The blend is a book that is essential for any veterinary student or veterinarian. Its companion website is a valuable addition.

Thirty years ago, Tony King, in the preface of his first edition, said he focused his book on the needs of veterinary students to learn neuroanatomy and neurophysiology. It is amazing how far neurology has come since then. Now we have hundreds of veterinary neurologists spread around the world discussing and communicating the results of new imaging techniques instantaneously to each other via the Internet. The large number of neurology residents in training in so many countries is impressive. All veterinary neu-rologists and general clinicians need Geoff Skerritt’s second edition as a reference source when questions about neuroanatomy arise. Few other sources can answer applied neuroanatomical questions as easily as this book. This second edition is not just for veterinary students!

The applicability of this book to the neuroanatomy and neurophysiology of all species of domestic mammals is especially useful. The straightforward explanations of applied neuroanatomy, as it affects the spectrum of structural variations across different species, are enlightening, not only to the students but also to the clinicians involved with all domestic mammals.

Geoff Skerritt is modest when he said he has just ‘updated the first edition’. The sec-ond edition is a very successful and major adaptation of the brilliantly simple teaching style of Tony King, reflecting the needs of modern veterinary clinicians and students.

Alan J. Parker (BSc, BVSc, MS, PhD, MRCVS, Dip ACVIM – neurology, Dip ECVN)

Emeritus Professor College of Veterinary Medicine

University of Illinois Urbana, IL, USA

Foreword to the Second Edition

xix

The first edition of this book was published in 1987 so that this second edition is long overdue. However, in the last thirty years there have been several notable developments in the study and practice of veterinary neurology, and an earlier publication of this book would certainly have missed some of the more recent advances. Professor Anthony King was a remarkable teacher and academic and I was fortunate to be one of his pupils, both as an undergraduate and as a staff member in his Department of Veterinary Anatomy at the University of Liverpool. I owe my enthusiasm for neuroanatomy and neurology to Tony and it has been a privilege to have the opportunity to carry on his work through the completion of the second edition of this book. The Preface that Tony wrote in the first edition of The Central Nervous System (originally intended to be Volume 1 of a series on Physiological and Clinical Anatomy of the Domestic Animals) emphasised his belief that a thorough knowledge of preclinical subjects was vital to a proper understanding of clinical science. The undoubted success of Tony as a teacher of anatomy and physiology was due largely to his very successful introduction of clinical application into the preclinical years. This edition provides several extra examples of recent origin, for example electrodiagnostic methods, stem cell transplantation and advanced imaging. It is not intended to be a textbook of these clinical techniques. but it does provide the reader with the logical relevance of the preclinical information which, otherwise, would be hard to learn.

My unique situation as a teacher of the nervous system, at both ends of the veterinary degree course at Liverpool, enabled me to develop my own clinical skills through the establishment of clinical neurology within the curriculum and a new referral service. In 1997, I was honoured to be elected President of the European College of Veterinary Neurology. My continued enthusiasm for veterinary neurology received interest and active support from Professor Donald Kelly and Professor Michael Clarkson, to both of whom I remain enormously grateful. Sandy DeLahunta, Tony Palmer and Tony King were the true pioneers of veterinary neuroscience, but they were followed by Simon Wheeler, Alan Parker, Rick LeCouteur and myself; we can all claim to have made our contributions to the development of the subject.

This second edition of Tony’s book again includes David Hogg’s chapter on topo-graphical anatomy of the nervous system, a valuable section written in a way that most readers will find easy to follow, no mean achievement for a subject full of complex terminology. I am grateful to Luca Motta, a work colleague and a Diplomat of the European College of Veterinary Neurology, for his excellent contribution on special

Preface

Prefacexx

senses and the diagnostic exercises. During the preparation of this edition we were saddened by the loss of our colleague, Ulrike Michal. I had invited her to contribute to the book, especially with respect to the illustrations, but her illness permitted her only to do some proof‐reading for which I was grateful but sorry that she could not do more.

Apart from the inevitable discussions on terminology, anatomy does not change very much. As a consequence much of Tony’s original book remains ‘valid’ today. My task has been to bring it up to date with clinical developments and advances while retaining the book’s primary role as an anatomy text. As in the first edition, effort has been made to conform to the Nomina Anatomica Veterinaria (NAV) and Nomina Histologica (NH). The aim has been to produce a text that is easy to read and logical in its arrangement. I  hope the reader will spot one or two areas of controversy and feel stimulated to investigate further to uncover where errors have become entrenched in the literature!

Geoff Skerritt

xxi

I am grateful to my wife, Judy, for her encouragement and help when I was battling with fonts, layouts, changed figure numbers and terminology, etc. Judy also wrote the section on evoked potentials in Chapter 23, a subject about which she knows more than I; thank you.

I am most grateful to Ian Elliott and Richard Trotter for their help in providing MRI and CT scans to illustrate images of the central nervous system and to Burgess Diagnostics Ltd for permission to include scans obtained with their scanners.

Acknowledgement

xxiii

About the Contributors

Dr Judith O. Skerritt BSc, MSc, PhD, Childer Thornton, Cheshire, UKShe is a mathemetician and has held teaching appointments in the UK and Canada. She gained her PhD at the University of Liverpool and, together with her husband, estab-lished a referral veterinary hospital in Cheshire. She is currently the Office Manager of the British Veterinary Hospital Association. She has been actively involved in brainstem auditory evoked potential testing for deafness in dogs. Judith contributed several sections of Chapter 24, concerned with brainstem auditory evoked potentials.

Dr Luca Motta DVM(Hons), DipECVN, MRCVS, Frodsham, Cheshire, UKHe graduated from the University of Perugia, Italy, in 2007. He completed an intern-ship at Chestergates Veterinary Hospital, UK, in 2009 and gained the Diploma of the European College of Veterinary Neurology in 2012. He has published widely in the subject of veterinary neurology. Luca contributed a major part of Chapter 9, the Special Senses, together with the Chapter on Clinical Neurology. He also put together some of the Diagnostic Exercises.

Dr David A. Hogg PhD, BVMS, DHLitt, St George’s University, GrenadaHe was Founding Dean at St Gorge’s University and Professor of Veterinary Anatomy 1998–2003. He has held teaching appointments at the Universities of Glasgow, Zambia and Nairobi and has held Honorary appointments at the Universities of London and Nottingham. David wrote Chapter 22 for the first edition and only a few changes have been made for the second edition. Topograhical anatomy is a difficult topic to write in a way that can be easily assimilated by the reader; David has achieved that and made a valuable contribution to this book.

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About the Companion Website

Don’t forget to visit the companion website for this book:

www.wiley.com/go/skerritt/kings‐anatomy

There you will find valuable materials designed to enhance your learning, including:

● Powerpoint slides with downloadable figures ● Multiple choice questions and answers ● Label the diagram exercises

1

King’s Applied Anatomy of the Central Nervous System of Domestic Mammals, Second Edition. Geoff Skerritt. © 2018 John Wiley & Sons Ltd. Published 2018 by John Wiley & Sons Ltd. Companion website: www.wiley.com/go/skerritt/kings-anatomy

1

Arterial Supply to the Brain

1.1 Basic Pattern of the Main Arteries Supplying the Brain

Five pairs of arteries supply the brain (Figure 1.1). The more rostral four of these arise from the cerebral arterial circle, popularly known as the circle of Willis, on the ventral surface of the brain; the cerebral arterial circle roughly circumscribes the hypothala-mus, with the stalk of the hypophysis (pituitary gland) in its centre. The fifth and most caudal arises from the basilar artery. The five pairs of arteries are:

1) the rostral cerebral artery;2) the middle cerebral artery, this being the largest cerebral artery in most mammals;3) the caudal cerebral artery;4) the rostral cerebellar artery; and5) the caudal cerebellar artery.

There are also various smaller arteries, which supply the medulla oblongata and pons.Although there are minor species variations, these vessels occur in mammals consist-

ently. The cerebellar arteries are variable in number and origin even within the same species: for example, in man and the horse, the rostral one may arise from the basilar artery. The three cerebral arteries are remarkably constant in amphibians and higher forms generally.

1.2 Basic Pattern of Incoming Branches to the Cerebral Arterial Circle

There are four potential incoming arterial channels to the cerebral arterial circle in mammals generally (Figure 1.2):

1) internal carotid artery;2) basilar artery: This midline artery is a continuation rostrally of the ventral spinal

artery. However, the blood that flows within the ventral spinal and basilar arteries has come from the vertebral artery via the segmental spinal arteries.

Arterial Supply to the Central Nervous System

King’s Applied Anatomy of the Central Nervous System of Domestic Mammals2

3) maxillary artery: This artery supplies the arterial circle by its so‐called anastomo-sing ramus, which joins the maxillary artery to the internal carotid artery.

4) vertebral artery: The vertebral artery connects to the internal carotid artery, and in some species it supplies the arterial circle directly by this route. However, it may also supply the circle indirectly via the ventral spinal artery and therefore the basilar artery (see above).

Because of the anatomy of these four arterial channels, the blood which distributes itself over the brain may be internal carotid blood, maxillary blood, or vertebral blood, or a combination of these (Figure 1.3).

1.3 Species Variations

In no domestic mammals are all four of these potential arterial channels to the cerebral arterial circle fully developed. Some of the channels are reduced in calibre or are even totally obliterated. The direction of flow in the remaining channels depends on the pressure gradients within the various vessels. The general relationships of these gradients have been worked out experimentally, thus establishing the direction of flow and the distribution of blood in each species. The following account applies to the intact live animal.

1.3.1 Dog, Man and most Mammals

Most mammals have what appears to be the most usual mammalian pattern of arterial supply to the brain (Figure 1.3(a)). The blood reaching the rostral half of the brain is internal carotid blood, but the caudal half of the brain is supplied by vertebral blood. This is because the pressure gradients are such that the flow of blood in the basilar artery is rostral. Consequently, vertebral blood reaches not only the cerebellar arteries but also the caudal cerebral artery.

Rostral cerebral artery

Middle cerebralartery

Internal carotidartery

Caudal cerebralartery

Rostral cerebellarartery

Caudal cerebellarartery

Basilarartery

Figure 1.1 Diagram of the cerebral arterial circle and its outgoing branches. The connection across the midline at the rostral end of the circle is inconstant in the dog and ruminants.