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

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