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John G. Nicholls

International School for Advanced Studies, Trieste, Italy

A. Robert Martin

Emeritus, University of Colorado School of Medicine

Paul A. Fuchs

The Johns Hopkins University School of Medicine

David A. Brown

University College London

Mathew E. Diamond

International School for Advanced Studies, Trieste, Italy

David A. Weisblat

University of California, Berkeley

Neuron

BrainFIFTH EDITION

From

to

Sinauer Associates, Inc.Publishers

Sunderland, Massachusetts USA

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PART I Introduction to the NervousSystem 1

CHAPTER 1 Principles of Signaling and

Organization 3

CHAPTER 2 Signaling in the Visual System 23

CHAPTER 3 Functional Architecture of the VisualCortex 43

PART II Electrical Properties ofNeurons and Glia 61

CHAPTER 4 Ion Channels and Signaling 63

CHAPTER 5 Structure of Ion Channels 77

CHAPTER 6 Ionic Basis of the Resting Potential 99

CHAPTER 7 Ionic Basis of the Action Potential 113

CHAPTER 8 Electrical Signaling in Neurons 129

CHAPTER 9 Ion Transport across Cell

Membranes 143

CHAPTER 10 Properties and Functions of Neuroglial

Cells 159

PART III IntercellularCommunication 183

CHAPTER 11 Mechanisms of Direct Synaptic

Transmission 185

CHAPTER 12 Indirect Mechanisms of SynapticTransmission 213

CHAPTER 13 Release of Neurotransmitters 243

CHAPTER 14 Neurotransmitters in the Central

Nervous System 273

CHAPTER 15 Transmitter Synthesis, Transport,

Storage, and Inactivation 299

CHAPTER 16 Synaptic Plasticity 317

PART IV Integrative Mechanisms 335

CHAPTER 17 Autonomic Nervous System 337

CHAPTER 18 Cellular Mechanisms of Behavior

in Ants, Bees, and Leeches 355

PART V Sensation and Movement 383CHAPTER 19 Sensory Transduction 385

CHAPTER 20 Transduction and Transmission

in the Retina 407

CHAPTER 21 Touch, Pain, and Texture

Sensation 433

CHAPTER 22 Auditory and Vestibular Sensation 453

CHAPTER 23 Constructing Perception 475

CHAPTER 24 Circuits Controlling Reflexes,

Respiration, and CoordinatedMovements 497

PART VI Development andRegeneration of theNervous System 529

CHAPTER 25 Development of the Nervous

System 531

CHAPTER 26 Critical Periods in Sensory

Systems 565

CHAPTER 27 Regeneration of Synaptic Connections

after Injury 589

PART VII Conclusion 613

CHAPTER 28 Open Questions 615

Brief Table of Contents

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CHAPTER 1 Principles of Signalingand Organization 3

Signaling in Simple Neuronal Circuits 4Complex Neuronal Circuitry in Relation to Higher

Functions 4

Organization of the Retina 5

Shapes and Connections of Neurons 5

Cell Body, Axons, and Dendrites 7

Techniques for Identifying Neurons and Tracing TheirConnections 7

Non-Neuronal Cells 8

Grouping of Cells According to Function 9

Complexity of Connections 9

Signaling in Nerve Cells 10Universality of Electrical Signals 10

Techniques for Recording Signals from Neurons withElectrodes 11

Noninvasive Techniques for Recordingand Stimulating Neuronal Activity 11

Spread of Local Graded Potentials and PassiveElectrical Properties of Neurons 13

Spread of Potential Changes in Photoreceptors andBipolar Cells 14

Properties of Action Potentials 14

Propagation of Action Potentials along NerveFibers 15

Action Potentials as the Neural Code 15

Synapses: The Sites for Cell-to-CellCommunication 15

Chemically Mediated Synaptic Transmission 15

Excitation and Inhibition 16

Electrical Transmission 17

Modulation of Synaptic Efficacy 17

Integrative Mechanisms 18

Complexity of the Information Conveyed by ActionPotentials 19

Reverse Traffic of Signals from Higher to LowerCenters 19

Higher Functions of the Brain 20

Cellular and Molecular Biology of Neurons 20

Signals for Development of the Nervous System 20

Regeneration of the Nervous System after Injury 21

CHAPTER 2 Signaling in theVisual System 23

Pathways in the Visual System 24

Convergence and Divergence of Connections 25Receptive Fields of Ganglion and

Geniculate Cells 26

Concept of Receptive Fields 26

The Output of the Retina 26

Ganglion and Geniculate Cell Receptive FieldOrganization 27

Sizes of Receptive Fields 28

Classification of Ganglion and Geniculate Cells 29

What Information Do Ganglion and Geniculate CellsConvey? 29

Box 2.1 Strategies for Exploring the Cortex 30

Cortical Receptive Fields 31

Responses of Simple Cells 31

Synthesis of the Simple Receptive Field 33

Responses of Complex Cells 35

Synthesis of the Complex Receptive Field 37

Receptive Fields: Units for Form Perception 38

Contents

PART I INTRODUCTION TO THE NERVOUS SYSTEM 1

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CHAPTER 6 Ionic Basis of theResting Potential 99

A Model Cell 100

Ionic Equilibrium 100

Electrical Neutrality 101

The Effect of Extracellular Potassium and Chloride onMembrane Potential 102

Membrane Potentials in Squid Axons 103

The Effect of Sodium Permeability 104

The Constant Field Equation 105

The Resting Membrane Potential 106

Chloride Distribution 107

An Electrical Model of the Membrane 107

Predicted Values of Membrane Potential 108

Contribution of the SodiumPotassium Pumpto the Membrane Potential 109

What Ion Channels Are Associated with the RestingPotential? 109

Changes in Membrane Potential 110

CHAPTER 7 Ionic Basis of the ActionPotential 113

Voltage Clamp Experiments 114

Capacitative and Leak Currents 114

Ionic Currents Carried by Sodium andPotassium 114

Selective Poisons for Sodiumand Potassium Channels 115

Box 7.1 The Voltage Clamp 116

Dependence of Ion Currents on MembranePotential 116

Inactivation of the Sodium Current 117

Sodium and Potassium Conductances as Functions ofPotential 118

Quantitative Description of Sodium

and Potassium Conductances 119

Reconstruction of the Action Potential 120

Threshold and Refractory Period 120Gating Currents 122

Mechanisms of Activation and

Inactivation 123

Activation and Inactivation of Single Channels 124

Afterpotentials 125

The Role of Calcium in Excitation 127

Calcium Action Potentials 127

Calcium Ions and Excitability 128

CHAPTER 8 Electrical Signaling inNeurons 129

Specific Electrical Properties of Cell Membranes 131

Flow of Current in a Nerve Fiber 131

Box 8.1 Relation between Cable Constants and

Specific Membrane Properties 133

Action Potential Propagation 134

Myelinated Nerves andSaltatory Conduction 134

Box 8.2 Classification of Vertebrate NerveFibers 135

Distribution of Channels in Myelinated Fibers 136

Geometry and Conduction Block 137

Conduction in Dendrites 137

Pathways for Current Flow between Cells 139

CHAPTER 9 Ion Transport across CellMembranes 143

The SodiumPotassium Exchange Pump 144

Biochemical Properties of SodiumPotassiumATPase 144

Experimental Evidence that the Pump IsElectrogenic 144

Mechanism of Ion Translocation 146

Calcium Pumps 147

Endoplasmic and Sarcoplasmic Reticulum Calcium

ATPase 147Plasma Membrane Calcium ATPase 147

SodiumCalcium Exchange 147

The NCX Transport System 148

Reversal of SodiumCalcium Exchange 148

SodiumCalcium Exchange in Retinal Rods 149

Chloride Transport 150

Inward Chloride Transport 150

Outward PotassiumChloride Cotransport 150

ChlorideBicarbonate Exchange 150

Transport of Neurotransmitters 151

Transport into Presynaptic Vesicles 151

Transmitter Uptake 152

Molecular Structure of Transporters 153

ATPases 154

SodiumCalcium Exchangers 155

Chloride Transporters 155

Transport Molecules for Neurotransmitters 155

Significance of Transport Mechanisms 156

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Modulation of Ion Channel Function by Receptor-

Activated G Proteins: Direct Actions 217

G Protein Activation of Potassium Channels 217

Box 12.2 Identifying Responses Mediated by GProteins 218

G Protein Inhibition of Calcium ChannelsInvolved in Transmitter Release 221

G Protein Activation of Cytoplasmic Second

Messenger Systems 222

-Adrenergic Receptors Activate Calcium Channels viaa G Proteinthe Adenylyl Cyclase Pathway 223

Box 12.3 Cyclic AMP as a SecondMessenger 225

Box 12.4 Phosphatidylinositol-4,5-bisphosphate(PIP2) and the phosphoinositide (PI) Cycle 227

G Protein Activation of Phospholipase C 228

Direct Actions of PIP2 229

G Protein Activation of Phospholipase A2 230

Convergence and Divergence of Signals

Generated by Indirectly Coupled Receptors 230

Retrograde Signaling via Endocannabinoids 231

Box 12.5 Formation and Metabolism ofEndocannabinoids 233

Signaling via Nitric Oxide and Carbon Monoxide 234

Calcium as an Intracellular Second Messenger 235

Actions of Calcium 237

Box 12.6 Measuring Intracellular Calcium 238

Prolonged Time Course of Indirect Transmitter

Action 239

CHAPTER 13 Release ofNeurotransmitters 243

Characteristics of Transmitter Release 244

Axon Terminal Depolarization and Release 244

Synaptic Delay 245

Evidence that Calcium Is Required for Release 246

Measurement of Calcium Entry into Presynaptic Nerve

Terminals 246Localization of Calcium Entry Sites 248

Transmitter Release by Intracellular ConcentrationJumps 249

Other Factors Regulating Transmitter Release 249

Quantal Release 250

Spontaneous Release of Multimolecular Quanta 251

Fluctuations in the End-Plate Potential 252

Statistical Analysis of the End-Plate Potential 252

Box 13.1 Statistical Fluctuation in QuantalRelease 253

Quantum Content at Neuronal Synapses 255

Number of Molecules in a Quantum 255

Number of Channels Activated by a Quantum 256Changes in Mean Quantal Size at the Neuromuscular

Junction 257

Nonquantal Release 257

Vesicles and Transmitter Release 258

Ultrastructure of Nerve Terminals 258

Morphological Evidence for Exocytosis 259

Release of Vesicle Contents by Exocytosis 261

Monitoring Exocytosis and Endocytosisin Living Cells 262

Mechanism of Exocytosis 264

High-Resolution Structure of Synaptic VesicleAttachments 264

Reuptake of Synaptic Vesicles 266

Vesicle Recycling Pathways 267

Ribbon Synapses 269

Vesicle Pools 270

CHAPTER 14 Neurotransmitters in theCentral Nervous System 273

Chemical Transmission in the CNS 274

Mapping Neurotransmitter Pathways 274

Box 14.1 The Discovery of Central Transmitters:I. The Amino Acids 275

Box 14.2 The Discovery of Central Transmitters:II. Neuropeptides 277

Visualizing Transmitter-Specific Neurons in LivingBrain Tissue 278

Key Transmitters 278

Glutamate 279

GABA (-Aminobutyric acid) and glycine 279

Acetylcholine 281

Biogenic Amines 287Adenosine Triphosphate (ATP) 290

Peptides 292

Substance P 293

Opioid Peptides 293

Orexins (Hypocretins) 294

Vasopressin and Oxytocin: The Social Brain 296

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CHAPTER 15 Transmitter Synthesis,Transport, Storage, and Inactivation 299

Neurotransmitter Synthesis 300

Synthesis of ACh 300

Synthesis of Dopamine and Norepinephrine 302

Synthesis of 5-Hydroxytryptamine (5-HT) 304Synthesis of GABA 305

Synthesis of Glutamate 305

Short- and Long-Term Regulation of TransmitterSynthesis 305

Synthesis of Neuropeptides 306

Storage of Transmitters in Synaptic Vesicles 307

Co-Storage and Co-Release 308

Axonal Transport 310

Rate and Direction of Axonal Transport 311

Microtubules and Fast Transport 311

Mechanism of Slow Axonal Transport 311

Removal of Transmitters from the Synaptic Cleft 313

Removal of ACh by Acetylcholinesterase 313

Removal of ATP by Hydrolysis 314

Removal of Transmitters by Uptake 314

CHAPTER 16 Synaptic Plasticity 317

Short-Term Changes in Signaling 318

Facilitation and Depression of Transmitter Release 318Post-Tetanic Potentiation and Augmentation 319

Mechanisms Underlying Short-Term SynapticChanges 320

Long-Term Changes in Signaling 323

Long-Term Potentiation 323

Associative LTP in Hippocampal Pyramidal Cells 323

Mechanisms Underlying the Induction of LTP 326

Silent Synapses 326

Presynaptic LTP 328

Long-Term Depression 329

LTD in the Cerebellum 331

Mechanisms Underlying LTD 331

Presynaptic LTD 332

Significance of Changes in Synaptic Efficacy 332

CHAPTER 17 Autonomic NervousSystem 337

Functions under Involuntary Control 338

Sympathetic and Parasympathetic NervousSystems 338

Synaptic Transmission in Autonomic Ganglia 340

M-Currents in Autonomic Ganglia 342

Transmitter Release by Postganglionic Axons 343

Purinergic Transmission 344

Box 17.1 The Path to Understanding SympatheticMechanisms 344

Sensory Inputs to the Autonomic Nervous System 345

The Enteric Nervous System 346Regulation of Autonomic Functions by the

Hypothalamus 347

Hypothalamic Neurons That Release Hormones 347

Distribution and Numbers of GnRH Cells 349

Circadian Rhythms 349

CHAPTER 18 Cellular Mechanismsof Behavior in Ants, Bees, andLeeches 355

From Behavior to Neurons and Vice Versa 356

Navigation by Ants and Bees 357

The Desert Ants Pathway Home 357

Polarized Light Detection by the Ants Eye 359

Strategies for Finding the Nest 361

Polarized Light and Twisted Photoreceptors 361

Additional Mechanisms for Navigation by Ants andBees 362

Neural Mechanisms for Navigation 364

Behavioral Analysis at the Level of Individual

Neurons in the CNS of the Leech 365

Leech Ganglia: Semiautonomous Units 365

Sensory Cells in Leech Ganglia 367

Motor Cells 370

Connections of Sensory and Motor Cells 371

Higher Order Behaviors in the Leech 373

Habituation, Sensitization, and Conduction Block 374

Circuits Responsible for the Production of RhythmicalSwimming 377

To Swim or to Crawl? Neurons that DetermineBehavioral Choices in the Leech 378

Why Should One Work on Invertebrate Nervous

Systems? 381

PART IV INTEGRATIVE MECHANISMS 335

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CHAPTER 19 SensoryTransduction 385

Stimulus Coding by Mechanoreceptors 386

Short and Long Receptors 386

Encoding Stimulus Parameters by StretchReceptors 387

The Crayfish Stretch Receptor 388

Muscle Spindles 389

Responses to Static and Dynamic Muscle Stretch 390

Mechanisms of Adaptation in Mechanoreceptors 391

Adaptation in the Pacinian Corpuscle 391

Direct Transduction by Mechanosensory Hair

Cells 392

Mechanosensory Hair Cells of the Vertebrate Ear 392

Structure of Hair Cell Receptors 393

Transduction by Hair Bundle Deflection 394

Tip Links and Gating Springs 395

Transduction Channels in Hair Cells 395

Adaptation of Hair Cells 396

Olfaction 397

Olfactory Receptors 397

The Olfactory Response 398

Cyclic Nucleotide-Gated Channels in Olfactory

Receptors 399Coupling the Receptor to Ion Channels 399

Odorant Specificity 400

Mechanisms of Taste (Gustation) 401

Taste Receptor Cells 401

Taste Modalities 402

Pain and Temperature Sensation in Skin 403

Activation and Sensitization of Nociceptors 404

CHAPTER 20 Transduction andTransmission in the Retina 407

The Eye 408

Anatomical Pathways in the Visual System 408

Layering of Cells in the Retina 408

Phototransduction in Retinal Rods and Cones 409

Arrangement and Morphology of Photoreceptors 410

Electrical Responses of Vertebrate Photoreceptors toLight 411

Visual Pigments 412

Absorption of Light by Visual Pigments 412

Structure of Rhodopsin 413

Cones and Color Vision 413

Color Blindness 415

Transduction 415

Properties of the Photoreceptor Channels 415

Molecular Structure of Cyclic GMPGatedChannels 416

The cGMP Cascade 416

Amplification through the cGMP Cascade 417

Responses to Single Quanta of Light 417

Box 20.1 Adaptation of Photoreceptors 418

Circadian Photoreceptors in the MammalianRetina 420

Synaptic Organization of the Retina 420

Bipolar, Horizontal, and Amacrine cells 420

Molecular Mechanisms of Synaptic Transmission in theRetina 421

Receptive Fields of Retinal Neurons 422

Responses of Bipolar Cells 423

Receptive Field Organization of Bipolar Cells 424

Rod Bipolar Cells 424

Horizontal Cells and Surround Inhibition 424

Significance of Receptive Field Organization of Bipolar

Cells 426Receptive Fields of Ganglion Cells 426

The Output of the Retina 426

Ganglion Cell Receptive Field Organization 427

Sizes of Receptive Fields 427

Classification of Ganglion Cells 427

Synaptic Inputs to Ganglion Cells Responsiblefor Receptive Field Organization 428

Amacrine Cell Control of Ganglion CellResponses 429

What Information Do Ganglion Cells Convey? 429

CHAPTER 21 Touch, Pain, and TextureSensation 433

From Receptors to Cortex 434

Receptors in the Skin 434

Anatomy of Receptor Neurons 436

Sensations Evoked by Afferent Signals 436

Ascending Pathways 437

Somatosensory Cortex 438

Pain Perception and its Modulation 439

PART V SENSATION AND MOVEMENT 383

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Somatosensory System Organization and Texture

Sensation in Rats and Mice 440

The Whiskers of Mice and Rats 440

Magnification Factor 440

Topographic Map of the Whiskers and ColumnarOrganization 441

Map Development and Plasticity 441

Box 21.1 Variation across Species in CorticalMaps 443

Texture Sensation through the Whiskers: PeripheralMechanisms 444

Texture Sensation through the Whiskers: CorticalMechanisms 445

Somatosensory System Organization and Texture

Sensation in Primates 446

Magnification Factor 446

Topographic Map of the Skin and Columnar

Organization 446Map Plasticity 447

Texture Sensation through the Fingertip: PeripheralMechanisms 447

Texture Sensation through the Fingertip: CorticalMechanisms 450

CHAPTER 22 Auditory and VestibularSensation 453

The Auditory System: Encoding the Frequency

Composition of Sound 455

The Cochlea 456Frequency Selectivity: Mechanical Tuning 456

Electromotility of Mammalian Cochlear HairCells 457

Efferent Inhibition of the Cochlea 458

Frequency Selectivity in Nonmammalian Vertebrates:Electrical Tuning of Hair Cells 461

Hair Cell Potassium Channels and ElectricalTuning 461

The Auditory Pathway: Transmission between HairCells and Eighth Nerve Fibers 463

Stimulus Coding by Primary Afferent Neurons 464Brainstem and Thalamus 464

Sound Localization 464

Auditory Cortex 466

The Vestibular System: Encoding Head Motion

and Position 467

Vestibular Hair Cells and Neurons 467

The Adequate Stimulus for the Saccule and Utricle 469

The Adequate Stimulus for the Semicircular Canals 470

The Vestibulo-Ocular Reflex 471

Higher Order Vestibular Function 471

CHAPTER 23 ConstructingPerception 475

What Is the Function of Cortical Processing? 476Tactile Working Memory Task and its Representation

in Primary Somatosensory Cortex 476

Behavioral Task 476

Neuronal Representation of Vibration Sensationsin SI 478

Replacement of Vibrations by Artificial Stimuli 479

Transformation from Sensation to Action 480

Activity in SI across Successive Stages of the Task 480

Activity in Regions beyond SI 481

Neurons Associated with Decision Making 483

Visual Object Perception in Primates 484

Object Perception and the Ventral Visual Pathway 484

Deficits in Object Perception 485

Images that Activate Neurons in the Ventral

Stream 485

Discovery of Responses to Complex Stimuli inMonkeys 485

The Special Case of Faces 485

Box 23.1 Functional Magnetic ResonanceImaging 487

Perceptual Invariance and Neuronal Response

Invariance 487

Dorsal Intracortical Visual Pathways and Motion

Detection 489

Transformation from Elements to Percepts 492

Merging of Features 492

Speed of Processing 493

Forms of Coding 493

TopDown Inputs 494

Further Processing 495

CHAPTER 24 Circuits Controlling

Reflexes, Respiration, and CoordinatedMovements 497

The Motor Unit 498

Synaptic Inputs to Motoneurons 499

Unitary Synaptic Potentials in Motoneurons 500

The Size Principle and Graded Contractions 500

Spinal Reflexes 501

Reciprocal Innervation 501

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Central Nervous System Control of Muscle Spindles 503

Flexor Reflexes 506

Generation of Coordinated Movements 506

Neural Control of Respiration 506

Locomotion 509

Sensory Feedback and Central Pattern GeneratorPrograms 511

Organization of Descending Motor Control 512

Terminology 512

Supraspinal Control of Motoneurons 512

Lateral Motor Pathways 512

Medial Motor Pathways 513

Motor Cortex and the Execution of Voluntary

Movement 514

What Do Motor Maps Mean? 515

Cellular Activity and Movement 516

Cortical Cell Activity Related to Direction of ArmMovements 516

Higher Control of Movement 517

Cerebellum and Basal Ganglia 519

The Cerebellum 519

Connections of the Cerebellum 519

Synaptic Organization of the Cerebellar Cortex 521

What Does the Cerebellum Do and How Does It DoIt? 523

The Basal Ganglia 524

Circuitry of the Basal Ganglia 525

Diseases of the Basal Ganglia 525

PART VI DEVELOPMENT AND REGENERATIONOF THE NERVOUS SYSTEM 529

CHAPTER 25 Development of theNervous System 531

Development: General Considerations 532

Genomic Equivalence and Cell Type Diversity 532

Cell Fate Maps Provide a Description of NormalDevelopment 533

Box 25.1 Conserved Signaling Pathways for EarlyDevelopment and Neurogenesis 534

Early Morphogenesis of the Nervous System 535

Patterning along Anteroposterior and Dorsoventral

Axes 537

Anteroposterior Patterning and Segmentation inHindbrain 538

Dorsoventral Patterning in the Spinal Cord 539

Cell Proliferation 541

Cell Proliferation in the Ventricular Zone 541

Cell Proliferation via Radial Glia 541

When Do Neurons Stop Dividing? AdultNeurogenesis 543

Migration 545

Migration of Cortical Neurons 545

Genetic Abnormalities of Cortical Layers in ReelerMice 547

Determination of Cell Phenotype 547

Lineage of Neurons and Glial Cells 547

Control of Transmitter Choice in the PeripheralNervous System 547

Changes in Receptors during Development 549

Axon Outgrowth and Growth Cone Navigation 550

Growth Cones, Axon Elongation, and the Role ofActin 550

Cell and Extracellular Matrix Adhesion Moleculesand Axon Outgrowth 550

Growth Cone Guidance: Target-Dependent andTarget-Independent Navigation 552

Target-Dependent Navigation via Guidepost Cells 552

Growth Cone Navigation along Gradients 553

Growth Factors and Survival of Neurons 555

Cell Death in the Developing Nervous System 555

Nerve Growth Factor 555

NGF in the Central Nervous System 556

The Neurotrophins and other Families of GrowthFactors 556

Formation of Connections 558

Establishment of the Retinotectal Map 558

Synapse Formation 559

Pruning and the Removal of PolyneuronalInnervation 560

Neuronal Activity and Synapse Elimination 561

General Considerations of Neural Specificity

and Development 561

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CHAPTER 26 Critical Periods inSensory Systems 565

The Visual System in Newborn Monkeys and

Kittens 566

Receptive Fields and Response Properties of CorticalCells in Newborn Animals 566

Ocular Dominance Columns in Newborn Monkeys andKittens 567

Postnatal Development of Ocular DominanceColumns 568

Effects of Abnormal Visual Experience in Early

Life 569

Blindness after Lid Closure 569

Responses of Cortical Cells after MonocularDeprivation 569

Relative Importance of Diffuse Light and Formfor Maintaining Normal Responses 569

Morphological Changes in the Lateral GeniculateNucleus after Visual Deprivation 569

Morphological Changes in the Cortex after VisualDeprivation 570

Critical Period for Susceptibility to Lid Closure 570

Recovery during the Critical Period 571

Requirements for Maintenance of Functioning

Connections in the Visual System 573

Binocular Lid Closure and the Role ofCompetition 573

Effects of Strabismus (Squint) 573

Changes in Orientation Preference 574Segregation of Visual Inputs without

Competition 574

Effects of Impulse Activity on the Developing VisualSystem 575

Synchronized Spontaneous Activity in the Absence ofInputs during Development 576

Role of -Aminobutyric Acid (GABA) and TrophicMolecules in Development of ColumnarArchitecture 577

Critical Periods in Somatosensory and OlfactorySystems 578

Sensory Deprivation and Critical Periodsin the Auditory System 578

Regulation of Synapse Formation by Activity in theCochlear Nucleus 580

Box 26.1 The Cochlear Implant 581

Critical Periods in the Auditory System of Barn

Owls 581

Effects of Enriched Sensory Experience in EarlyLife 583

Critical Periods in Humans and ClinicalConsequences 585

CHAPTER 27 Regeneration of SynapticConnections after Injury 589

Regeneration in the Peripheral Nervous System 590

Wallerian Degeneration and Removal of Debris 590

Retrograde Transsynaptic Effects of Axotomy 591

Effects of Denervation on Postsynaptic Cells 592

The Denervated Muscle Membrane 592

Appearance of New ACh Receptors (AChRs)after Denervation or Prolonged Inactivity ofMuscle 592

Synthesis and Degradation of Receptors in DenervatedMuscle 592

Role of Muscle Inactivity in DenervationSupersensitivity 593

Role of Calcium in Development of Supersensitivityin Denervated Muscle 595

Supersensitivity of Peripheral Nerve Cellsafter Removal of Synaptic Inputs 596

Susceptibility of Normal and Denervated Muscles toNew Innervation 597

Role of Schwann Cells and Microglia in AxonOutgrowth after Injury 597

Denervation-Induced Axonal Sprouting 598

Appropriate and Inappropriate Reinnervation 598

Basal Lamina, Agrin, and the Formation

of Synaptic Specializations 599

Identification of Agrin 601

The Role of Agrin in Synapse Formation 602

Mechanism of Action of Agrin 603

Regeneration in the Mammalian CNS 605

Glial Cells and CNS Regeneration 605

Schwann Cell Bridges and Regeneration 606

Formation of Synapses by Axons Regenerating in theMammalian CNS 607

Regeneration in Immature Mammalian CNS 607

Neuronal Transplants 609

Prospects for Developing Treatment of Spinal CordInjury in Patients 610

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