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

GEOFF SKERRITT is an RCVS and European Specialist in Veterinary Neurology, and a Diplomate and former President of the European College of Veterinary Neurology. In 1997 Geoff was one of the founders of VetMRI, the first mobile veterinary MRI facility in Europe. He is the founder and former Director of ChesterGates Animal Referral Hospital, a leading multi-discipline veterinary referral centre in the UK. He began his career as a Lecturer in veterinary anatomy at the University of Liverpool, UK. Enthusiasm for neuroanatomy led to a developing interest in veterinary neurology and the establishment of neurology in the curriculum and clinics at the University of Liverpool School of Veterinary Science. Geoff is a popular speaker at meetings and congresses and has published widely in the subjects of veterinary neuroanatomy and neurology.

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 1

1.1 Basic Pattern of the Main Arteries Supplying the Brain 1

1.2 Basic Pattern of Incoming Branches to the Cerebral Arterial Circle 1

1.3 Species Variations 2

1.4 Summary of the Significance of the Vertebral Artery as a Source of Blood to the Brain 5

1.5 Humane Slaughter 6

1.6 Rete Mirabile 7

Superficial Arteries of the Spinal Cord 8

1.7 Main Trunks 8

1.8 Anastomosing Arteries 8

1.9 Segmental Arteries to the Spinal Cord 10

1.10 General Principles Governing the Distribution of Arteries below the Surface of the Neuraxis 10

1.11 The Deep Arteries of the Spinal Cord 10

1.12 The Problem of Pulsation 11

1.13 Arterial Anastomoses of the Neuraxis 11

2 The Meninges and Cerebrospinal Fluid 13

Meninges 13

2.1 General Anatomy of the Cranial and Spinal Meninges 13

2.2 Anatomy of the Meninges at the Roots of Spinal and Cranial Nerves 14

2.3 The Spaces around the Meninges 14

2.4 Relationship of Blood Vessels to the Meninges 16

2.5 The Filum Terminale 16

2.6 The Falx Cerebri and Membranous Tentorium Cerebelli 16

Cerebrospinal Fluid 16

2.7 Formation of Cerebrospinal Fluid 16

2.8 The Choroid Plexuses 16

2.9 Mechanism of Formation of Cerebrospinal Fluid 17

2.10 Circulation of Cerebrospinal Fluid 17

2.11 Drainage of Cerebrospinal Fluid 19

2.12 Functions of Cerebrospinal Fluid 20

2.13 Blood‐brain Barrier 21

2.14 Collection of Cerebrospinal Fluid 22

2.15 Clinical Conditions of the Cerebrospinal Fluid System 23

3 Venous Drainage of the Spinal Cord and Brain 25

The Cranial System of Venous Sinuses 25

3.1 General Plan 25

3.2 The Components of the Dorsal System of Sinuses 27

3.3 The Components of the Ventral System of Sinuses 28

3.4 Drainage of the Cranial Sinuses into the Systemic Circulation 28

The Spinal System of Venous Sinuses 29

3.5 General Plan 29

3.6 Connections to the Cranial System of Sinuses 29

3.7 Territory Drained by the Spinal System of Sinuses 29

3.8 Drainage of the Spinal Sinuses into the Systemic Circulation 29

Clinical Significance of the Venous Drainage of the Neuraxis 30

3.9 Spread of Infection in the Head 30

3.10 Paradoxical Embolism 30

3.11 Venous Obstruction 30

3.12 Angiography for Diagnosis 31

4 The Applied Anatomy of the Vertebral Canal 33

The Anatomy of Epidural Anaesthesia and Lumbar Puncture 33

4.1 The Vertebrae 33

4.2 Spinal Cord 33

4.3 Meninges 35

4.4 Lumbar Puncture 35

4.5 Epidural Anaesthesia in the Ox 35

4.6 Injuries to the Root of the Tail 36

The Anatomy of the Intervertebral Disc 36

4.7 The Components of the Disc 36

4.8 Senile Changes 38

4.9 Disc Protrusion 38

4.10 Fibrocartilaginous Embolism 41

Malformation or Malarticulation of Vertebrae 41

4.11 The ‘Wobbler Syndrome’ in the Dog 41

4.12 The Wobbler Syndrome in the Horse 41

4.13 Atlanto‐Axial Subluxation in Dogs 42

4.14 Anomalous Atlanto‐Occipital Region in Arab Horses 42

4.15 Other Vertebral Abnormalities in Dogs 42

5 The Neuron 43

The Anatomy of Neurons 43

5.1 General Structure 43

5.2 The Axon 46

5.3 Epineurium, Perineurium and Endoneurium 50

5.4 The Synapse 51

5.5 Phylogenetically Primitive and Advanced Neurons 54

5.6 Axonal Degeneration and Regeneration in Peripheral Nerves 55

5.7 Regeneration and Plasticity in the Neuraxis 58

5.8 Stem Cells and Olfactory Ensheathing Cells 58

5.9 The Reflex Arc 59

5.10 Decussation: The Coiling Reflex 60

6 The Nerve Impulse 63

Excitation and Inhibition 63

6.1 Ion Channels and Gating Mechanisms 63

6.2 The Membrane Potential 64

6.3 The Excitatory Postsynaptic Potential 64

6.4 The Inhibitory Postsynaptic Potential 67

6.5 The Receptor Potential 68

6.6 The End‐plate Potential 69

6.7 Summary of Decremental Potentials 70

6.8 The Action Potential 71

6.9 Concerning Water Closets 73

6.10 Transducer Mechanisms of Receptors 73

6.11 Astrocytes 76

6.12 Oligodendrocytes 76

6.13 Microglia 77

7 Nuclei of the Cranial Nerves 79

General

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

7.1 Shape and Position of the Central Canal 79

7.2 Fragmentation of the Basic Columns of Grey Matter 79

7.3 Development of an Additional Component; Special Visceral Efferent 80

7.4 The Cranial Nerves of the Special Senses 82

7.5 Summary of the Architectural Principles of the Nuclei of the Cranial Nerves 82

Names, Topography and Functions of the Cranial Nerve Nuclei 82

7.6 Somatic Afferent Nucleus 82

7.7 Visceral Afferent Nucleus 85

7.8 Visceral Efferent Nuclei 85

7.9 Special Visceral Efferent Nuclei 86

7.10 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 89

8.1 Conscious Sensory Modalities 89

8.2 Peripheral Receptors of Touch, Pressure and Joint Proprioception 91

8.3 Pathways of Touch, Pressure and Joint Proprioception 92

Clinical Conditions Affecting the Medial Lemniscal System 94

8.4 Effects of Lesions in the Dorsal Funiculus 94

Pain Pathways 96

8.5 Peripheral Receptors of Pain 96

8.6 Spinothalamic Tract of Man 97

8.7 Spinothalamic Pathways in Domestic Mammals 100

8.8 Spinocervical Tract (Spinocervicothalamic Tract) 100

8.9 Species Variations in the Medial Lemniscal System 100

8.10 Somatotopic Localisation 101

8.11 Blending of Tracts in the Spinal Cord 101

8.12 Summary of the Medial Lemniscus System 101

9 The Special Senses 103

Vision 103

9.1 Neuron 1 103

9.2 Neuron 2 103

9.3 Neuron 3 103

Hearing 106

9.4 Neuron 1 106

9.5 Neuron 2 106

9.6 Neuron 3 106

Balance 107

9.7 Neuron 1 107

9.8 Neuron 2 107

Taste 112

9.9 Neuron 1 112

9.10 Neuron 2 112

9.11 Neuron 3 112

Olfaction Proper: The Sense of Smell 113

9.12 Neuron 1 113

9.13 Neuron 2 114

9.14 Neuron 3 114

Summary of the Conscious Sensory Systems 117

10 Spinocerebellar Pathways and Ascending Reticular Formation 119

10.1 Spinocerebellar Pathways 119

10.2 Ascending Reticular Formation 119

Spinocerebellar Pathways 120

10.3 Hindlimbs 120

10.4 Forelimbs 122

10.5 Projections of Spinocerebellar Pathways to the Cerebral Cortex 123

10.6 Functions of the Spinocerebellar Pathways 124

10.7 Species Variations 124

Ascending Reticular Formation 124

10.8 Organisation 124

Functions of the Ascending Reticular Formation 128

10.9 Arousal 128

10.10 Transmission of Deep Pain 128

10.11 Summary of Spinocerebellar Pathways and Ascending Reticular Formation 132

11 Somatic Motor Systems 135

Somatic Efferent Neurons 135

11.1 Motor Neurons in the Ventral Horn of the Spinal Cord 135

Muscle Spindles 137

11.2 Structure of the Muscle Spindle 137

11.3 The Mode of Operation of the Muscle Spindle 137

11.4 Role of Muscle Spindles in Posture and Movement 139

11.5 Golgi Tendon Organs 139

11.6 Muscle Tone 140

11.7 Motor Unit 141

11.8 Recruitment of Motor Units 141

11.9 Summary of Ways of Increasing the Force of Contraction of a Muscle 142

The Final Common Path 142

11.10 Algebraic Summation at the Final Common Path 142

11.11 Renshaw Cells 142

11.12 Lower Motor Neuron 142

11.13 Integration of the Two Sides of the Neuraxis 143

12 Pyramidal System 145

Pyramidal Pathways 145

12.1 The Neuron Relay 145

Feedback Pathways of the Pyramidal System 148

12.2 Feedback of the Pyramidal System 148

Comparative Anatomy of the Pyramidal System 149

12.3 Species Variations in the Primary Motor Area of the Cerebral Cortex 149

12.4 Species Variations in the Pyramidal System 150

12.5 The Function of the Pyramidal System 150

Clinical Considerations 151

12.6 Effects of Lesions in the Pyramidal System 151

12.7 Validity of the Distinction between Pyramidal and Extrapyramidal Systems 152

13 Extrapyramidal System 153

Motor Centres 153

13.1 Nine Command Centres 153

13.2 The Cerebral Cortex 153

13.3 Basal Nuclei and Corpus Striatum 154

13.4 Midbrain Reticular Formation 155

13.5 Red Nucleus 155

13.6 Mesencephalic Tectum 155

13.7 Pontine Motor Reticular Centres 156

13.8 Lateral Medullary Motor Reticular Centres 156

13.9 Medial Medullary Motor Reticular Centres 156

13.10 Vestibular Nuclei 156

Spinal Pathways 156

13.11 Pontine and Medullary Reticulospinal Tracts 156

13.12 Rubrospinal Tract 158

13.13 Vestibulospinal Tract 159

13.14 Tectospinal Tract 159

13.15 The Position in the Spinal Cord of the Tracts of the Extrapyramidal System 159

13.16 Summary of the Tracts of the Extrapyramidal System 159

14 Extrapyramidal Feedback and Upper Motor Neuron Disorders 161

Feedback of the Extrapyramidal System 161

14.1 Neuronal Centres of the Feedback Circuits 161

14.2 Feedback Circuits 161

14.3 Balance between Inhibitory and Facilitatory Centres 164

14.4 Clinical Signs of Lesions in Extrapyramidal Motor Centres in Man 165

14.5 Clinical Signs of Lesions in the Basal Nuclei in Domestic Animals 166

14.6 Upper Motor Neuron Disorders 166

15 Summary of the Somatic Motor Systems 169

The Motor Components of the Neuraxis 169

15.1 Pyramidal System 169

15.2 Extrapyramidal System 170

15.3 Distinction between Pyramidal and Extrapyramidal Systems 171

Clinical Signs of Motor System Injuries 171

15.4 Functions of the Pyramidal and Extrapyramidal Systems: Effects of Injury to the Motor Command Centres 171

15.5 Upper Motor Neuron 171

15.6 Lower Motor Neuron 172

15.7 Summary of Projections onto the Final Common Path 173

16 The Cerebellum 175

Afferent Pathways to the Cerebellum 175

16.1 Ascending from the Spinal Cord 175

16.2 Feedback Input into the Cerebellar Cortex 175

Arterial Supply to the Brain 177

Summary of Pathways in the Cerebellar Peduncles 178

16.3 Caudal Cerebellar Peduncle 179

16.4 Middle Cerebellar Peduncle 179

16.5 Rostral Cerebellar Peduncle 179

Rostral Cerebellar Peduncle 179

16.6 Vestibular Areas 179

16.7 Proprioceptive Areas 179

16.8 Feedback Areas 180

Functions of the Cerebellum 180

16.9 Co‐ordination and Regulation of Movement 180

16.10 Control of Posture 181

16.11 Ipsilateral Function of the Cerebellum 181

16.12 Summary of Cerebellar Function 181

16.13 Functional Histology of the Cerebellum 182

Clinical Conditions of the Cerebellum 184

16.14 The Three Cerebellar Syndromes 184

16.15 Cerebellar Disease in Domestic Mammals and Man 185

17 Autonomic Components of the Central Nervous System 187

Neocortex and Hippocampus 187

17.1 Cortical Components 187

17.2 Hippocampus 188

Diencephalon 188

17.3 Hypothalamus 188

The Autonomic Functions of the Hypothalamus 190

17.4 Amygdaloid Body and Septal Nuclei 192

17.5 Habenular Nuclei 193

17.6 Hindbrain Autonomic Areas 193

The Autonomic Areas of the Hindbrain 193

17.7 Autonomic Motor Pathways in the Spinal Cord 194

17.8 Ascending (Afferent) Visceral Pathways in the Spinal Cord and Brainstem 195

Clinical Disorders of the Autonomic System 195

17.9 Effects of Lesions in Autonomic Pathways 195

17.10 Summary of Descending Autonomic Pathways 197

18 The Cerebral Cortex and Thalamus 199

Cerebral Cortex 199

18.1 Projection Areas and Association Areas 199

18.2 Instinct 200

18.3 Cerebral Cortex in Primitive Mammals 200

18.4 Cerebral Cortex in the Cat and Dog 200

18.5 Conditioned Reflexes 200

18.6 Cerebral Cortex in Man 201

18.7 Cognitive Association Area in Man 202

18.8 Cognitive Association Area in Carnivores 203

18.9 Interpretative Association Area in Man 204

18.10 Interpretative Association Area in Carnivores 204

18.11 Frontal Association Area in Man 204

18.12 Frontal Association Area in Carnivores 205

18.13 Corpus Callosum 205

Clinical Conditions of the Cerebral Cortex 205

18.14 Effects of Extensive Damage to the Cerebral Hemisphere in Domestic Mammals 205

18.15 Seizures 207

Histology of the Cerebral Cortex 208

18.16 Histology of the Cerebral Cortex 208

Thalamus 208

18.17 Ventral Group of Thalamic Nuclei 209

18.18 The Lateral Group 210

18.19 Central (or Intralaminar) Group 210

18.20 Dorsomedial Group 210

18.21 Summary of Incoming Afferent Paths to the Thalamus: 210

18.22 Summary of the Projections from the Thalamus to the Cerebral Cortex 211

18.23 Summary of Functions of the Thalamus: 211

18.24 Clinical Effects of Lesions of the Thalamus in Domestic Mammals 212

18.25 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 215

19.1 The Development of the Brain 215

19.2 The Development of the Spinal Cord 217

19.3 The Development of the Neural Crest 217

Evolution of the Vertebrate Forebrain 218

19.4 Primitive Vertebrates 218

19.5 Contemporary Amphibian 218

19.6 Contemporary Advanced Reptile 219

19.7 Mammal 220

19.8 Bird 221

19.9 Major Homologies in Mammals and Birds 222

Evolution of the Capacity to Differentiate Sensory Modalities 223

19.10 Lower Vertebrates, Including Amphibians 223

19.11 Advanced Reptiles and Birds 223

19.12 Mammals 223

Special Features of the Avian Brain 223

19.13 Size of the Brain 223

19.14 Poor Development of the Cerebral Cortex 223

19.15 External Striatum 224

19.16 Colliculi: The Optic Lobe 224

19.17 Olfactory Areas 224

19.18 Cerebellum 225

19.19 Spinocerebellar Pathways 226

19.20 Cuneate and Gracile Fascicles 226

19.21 Motor Spinal Pathways 227

20 Clinical Neurology 229

20.1 Mental Status 229

20.2 Posture 230

20.3 Gait 230

20.4 Examination of the Cranial Nerves: Tests and Observations 232

Testing Postural and Locomotor Responses 243

20.5 Tonic Neck and Eye Responses 243

20.6 Proprioceptive Positioning Responses 243

20.7 Placing Responses 244

20.8 Extensor Postural Thrust 245

20.9 Hopping 245

20.10 Wheelbarrow Test 245

20.11 Hemiwalking 246

20.12 Righting 247

20.13 Blindfolding 247

20.14 Circling Test 247

20.15 Sway Test 247

Examination of Spinal Reflexes 247

20.16 Withdrawal (Flexor) Reflex 247

20.17 Patellar Tendon Reflex 249

20.18 Triceps Tendon Reflex 250

20.19 Biceps Tendon Reflex 250

20.20 Cutaneous Trunci/Colli (Formerly Panniculus) Reflex 250

20.21 Perineal Reflex 251

20.22 Crossed Extensor Reflex 251

20.23 Babinski Reflex 251

Other Tests 252

20.24 Assessment of Muscle Tone 252

20.25 Testing Conscious Pain Responses 252

20.26 Detecting Discomfort 252

20.27 Testing the Sympathetic System 252

20.28 Case Sheet 254

21 Imaging Techniques for Study of the Central Nervous System 257

General Considerations 257

21.1 Species 257

21.2 Objectives of Imaging in Clinical Neurology 257

21.3 Computed Tomography and Magnetic Resonance Imaging 258

21.4 The Use of Contrast Agents in Imaging 260

Intracranial Structures 262

21.5 Positioning of the Head 262

21.6 Breed and Age Variation in Images of the Head 262

Vertebral Column 263

21.7 Positioning of the Patient 263

21.8 Imaging the Vertebral Column 264

21.9 Contrast Radiography of the Vertebral Column 267

22 Topographical Anatomy of the Central Nervous System 269

Spinal Cord 269

22.1 Regions of the Spinal Cord 269

22.2 Segments of Spinal Cord and their Relationship to Vertebrae 270

22.3 General Organisation of Grey and White Matter 270

22.4 Dorsal, Lateral and Ventral Horns of Grey Matter 271

22.5 Laminae of Grey Matter 272

22.6 Funiculi of White Matter 272

22.7 Tracts of the White Matter 273

Medulla Oblongata 274

22.8 Gross Structure 274

22.9 Cranial Nerves 274

22.10 Ventricular System 275

22.11 Internal Structure 277

Pons 280

22.12 Gross Structure 280

22.13 Cranial Nerves 280

22.14 Ventricular System 281

22.15 Internal Structure 281

Midbrain 283

22.16 Gross Structure 283

22.17 Cranial Nerves 283

22.18 Ventricular System 284

22.19 Internal Structure 284

Diencephalon 288

22.20 Gross Structure 288

22.21 Cranial Nerves 289

22.22 Ventricular System 289

22.23 Internal Structure 290

Cerebellum 293

22.24 Gross Structure 293

22.25 Internal Structure 293

22.26 Cerebellar Peduncles 294

Cerebral Hemispheres 295

22.27 Gross Structure 295

22.28 Ventricular System 296

22.29 Internal Structure 297

23 Electrodiagnostics 303

23.1 Introduction 303

23.2 Electromyography 303

23.3 Nerve Conduction Velocity 304

23.4 Electroencephalography 304

23.5 Evoked Potentials 305

23.6 Electroretinography 307

23.7 Intra‐operative Monitoring of Spinal Cord Function 307

24 Diagnostic Exercises 309

24.1 Introduction 309

24.2 Solutions to Diagnostic Exercises 317

Appendix 325

Further Reading 335

Index 347