Control of Human Voluntary Movement

The human motor system is unique. It talks, walks and can play the piano from a remarkably early age. But it is difficult to study. One cannot impale single neurones with electrodes or lesion discrete areas of the nervous system in man. However, data gleaned from such elegant experiments in lower species that walk on four feet may not reflect the organisation of human motor mechanisms. John Rothwell is one of a small band of human-motor physiologists who have followed the dictum 'The proper study of mankind is man'. In this book, he brings together what is known about human motor physiology in an eminently readable and critical fashion. Of course, there is a stimulating symbiosis between animal and human experimental motor physiology, and this is effected by the integration of critical information that can only be obtained from work on animals with what is known about man. Many disciplines have interest in the mechanisms of human voluntary movement - physiologists, psychologists, physiotherapists and clinicians, be they neurologists or those working in orthopaedics, physical medicine or rehabilitation. All will find John Rothwell's book invaluable. To the beginner it provides an excellent introduction to the subject. To the expert it presents a coherent review of current knowledge and areas of uncertainty. What is abundantly clear is how much more remains to be discovered about how man controls movement. The stimulus provided by this volume will be invaluable to thought and experiment.

1. Introduction. Plans, Strategies and Actions.- Categories of Muscles.- Problems of Moving.- A Legacy.- 2. Mechanical Properties of Muscles.- Review of Muscle Anatomy.- The Sliding Filament Hypothesis of Muscle Contraction.- Mechanical Properties of Muscle.- Studies on Tetanically Activated Isolated Muscle.- The Length-Tension Relationship.- Twitch Contractions at Different Muscle Lengths.- Force-Velocity Relationship.- The Effect of the Rate of Muscle Stimulation.- Behaviour of Isolated Muscle Stimulated at Subtetanic Rates.- Asynchronous Activation of Muscle.- Length-Tension Relationship at Different Levels of Muscle Activation.- Forced Lengthening of Partially Activated Muscle.- Muscle Mechanics in Intact Man.- Effects of Muscle Properties on Control of Movement.- Effects Arising from the Length-Tension Relationship.- Force Production at Different Muscle Lengths.- Stiffness of Muscle.- Effects Arising from the Force-Velocity Relationship.- Efficiency of Muscle Contraction.- Lengthening Contractions.- Intrinsic Feedback Control of Muscle Contraction.- A Theory of Movement Control which Makes Use of the Mechanical Properties of Muscle.- 3. The Motor Unit.- The Concept of the Motor Unit.- Twitch and Tonic Muscle Fibres.- Physiological Investigation of the Motor Unit.- Territory and Size of Motor Units.- Differences in the Contraction of Motor Units.- Speed of Contraction and Fatiguability.- Twitch Tension and Specific Twitch Tension.- Post-tetanic Potentiation.- Size and Conduction Velocity of Motor Axons.- Summary.- Histochemical and Biochemical Classification of Muscle Fibres.- Correlation between Histochemical and Physiological Classifications of Motor Units.- Some Electrophysiological Properties of Motoneurones.- Synaptic Inputs to Motoneurones.- Input Resistance of Motoneurones.- Firing Patterns of Motoneurones.- Control of Motor Units and their Recruitment Order.- Mechanisms Responsible for the Recruitment Order of Motoneurones.- Exceptions to the Normal Order of Recruitment.- Examples of Motoneurone Recruitment during Normal Movement.- The Study of Motor Units in Human Physiology.- Recording Motor Units in Man.- Histochemistry of Human Motor Units.- Mechanical Properties of Human Motor Units.- Recruitment Order of Motor Units in Man.- Changes in Recruitment Order.- Firing Frequency of Human Motor Units.- Gradation of Force in Human Muscle Contraction.- Muscle Fatigue.- Pathophysiology of the Motor Unit.- The Normal Electromyogram.- The Electromyogram in Neurogenic Diseases.- The Electromyogram in Myopathic Diseases.- Changes in Firing Rate and Recruitment Order of Motor Units.- 4. Proprioceptors in Muscle, Joint and Skin.- Muscle Receptors: I. The Muscle Spindle.- Anatomy.- Physiology of Spindle Afferent Responses.- The Effect of ? Activity on Spindle Afferent Responses.- Response of Spindle Endings to Very Small Displacements.- Muscle Receptors: II. Golgi Tendon Organs.- Anatomy.- Physiology of Golgi Tendon Organ Responses.- Muscle Receptors: III. Other Types of Ending.- Joint Receptors.- Anatomy.- Physiology.- Cutaneous Mechanoreceptors.- Recordings from Human Afferent Nerve Fibres.- Muscle Spindles.- Golgi Tendon Organs.- Cutaneous Mechanoreceptors.- Contribution of Muscle Afferents to Sensation.- 5. Reflex Pathways in the Spinal Cord.- Classification of Nerve Fibres.- Reflex Pathways from la Muscle Spindle Afferents.- Anatomy.- Electrophysiology.- Monosynaptic Excitation.- Disynaptic Inhibition.- Polysynaptic Actions.- Reflex Pathways from lb Tendon Organ Afferents.- Anatomy.- Electrophysiology.- Reflex Pathways from Group II Muscle Afferents and the ‘Flexor Reflex Afferents’.- Anatomy.- Electrophysiology.- The Renshaw Cell.- Integration in Spinal Reflex Pathways.- Convergence onto the la Inhibitory Interneurone.- Convergence onto Ib Interneurones.- Comments on Convergence.- Presynaptic Inhibition.- 6. Functional Consequences of Activity in Spinal Reflex Pathways.- The Stretch Reflex in Animals.- Stretch Reflexes in Human Muscles.- The Tendon Jerk.- Long-latency Stretch Reflexes.- Vibration Reflexes.- The Servo Hypothesis and Alpha-Gamma Coactivation.- The Servo Theory.- Alpha-gamma Coactivation.- In Man.- In the Cat.- The Regulation of Stiffness Hypothesis and lb Effects.- Other Spinal Reflex Pathways.- Reciprocal Ia Inhibition.- Renshaw Inhibition.- Cutaneous Reflexes.- Nociceptive Cutaneous Reflexes in Man.- Low Threshold Cutaneous Reflexes in Man.- Pathophysiology of the Stretch Reflex: Disorders of Muscle Tone.- Hypotonus.- Hypertonus.- Spasticity v. Rigidity.- Reasons for the Increased Tendon Jerks in Spasticity.- Clasp-knife Phenomenon.- Changes in Muscle Tone Produced by Changes in the Mechanical Properties of Muscle.- Pathophysiology of Other Reflex Pathways.- Effects of Spinal Cord Transection.- Disynaptic Reciprocal Inhibitory Pathway.- Renshaw Cell Inhibition.- 7. Ascending and Descending Pathways of the Spinal Cord.- Ascending Pathways.- Afferent Input to the Spinal Cord.- Pathways to Thalamus and Cerebral Cortex.- Dorsal Column Pathway.- Spinocervical Pathway.- Spinothalamic Tract.- Thalamic Terminations of Somatic Afferents.- Pathways to the Cerebellum.- Dorsal Spinocerebellar and Cuneocerebellar Tracts.- Ventral and Rostral Spinocerebellar Tracts.- Spino-olivary-cerebellar Tracts.- Ascending Pathways to Other Structures.- Spinoreticular Tract.- Spinovestibular and Spinotectal Pathways.- Descending Motor Pathways.- Pyramidal Tract.- Rubrospinal Tract.- Vestibulospinal Tracts.- Reticulospinal Tracts.- Tectospinal and Interstitiospinal Tracts.- Summary of Descending Pathways.- 8. Cerebral Cortex.- Structure of Cerebral Cortex.- Sub-areas of Cerebral Cortex.- Which are the Motor Areas of Cortex?.- Cytoarchitecture and Connections of Cortical Motor Areas.- Cytoarchitecture.- Thalamic Inputs of Cortical Motor and Sensory Areas.- Cortico-cortical Inputs of the Motor Areas.- Outputs of Cortical Motor Areas.- Detailed Electrophysiology of Primary Motor (MI) Cortex.- Motor Cortex Mapping.- Corticospinal Localisation in MI.- Intracortical Microstimulation.- Stimulation of Motor Cortex in Man.- The Pyramidal Tract.- Motor Cortex Cell Activity During Voluntary Movements.- Timing of Discharge.- Relationship of Discharge to Movement Parameters.- Role of Small Pyramidal Tract Cells.- Sensory Input to Motor Cortex.- Controversy Over the Route by Which Afferent Input Reaches Motor Cortex.- Relation between Sensory Input and Motor Output.- Cutaneous Inputs.- Deep Inputs.- Transcortical Reflexes.- Other Motor Areas of Cortex.- Premotor Cortex.- Resumé of Anatomical Connections.- Effects of Electrical Stimulation.- Electrical Recording and Lesion Studies.- Grasp Reflexes and Spasticity.- Supplementary Motor Area.- Resumé of Anatomical Connections.- Effects of Electrical Stimulation.- Electrical Recording and Lesion Studies.- Electrical Recording.- Blood Flow.- Lesion Studies.- Motor Functions of Parietal Cortex.- Primary and Secondary Sensory Areas.- Parietal areas 5 and 7.- Lesion Studies.- Electrical Recording.- Pathophysiology of Motor Areas of Cerebral Cortex.- Epilepsy and Myoclonus.- Jacksonian Seizures.- Cortical Myoclonus.- Lesions of Descending Pathways.- Capsular Lesions.- The Effect of Pyramidal Tract Lesions.- Effects of Lesions of Other Descending Tracts.- Apraxia.- Premovement Potentials.- 9. The Cerebellum.- Cerebellar Anatomy.- Subdivisions of the Cerebellum.- Gross Anatomical Divisions.- Phylogenetic Divisions.- Divisions Based on Input and Output Arrangements.- Afferents.- Efferents.- Afferent Connections of the Cerebellum.- Direct Spinal Input.- Direct Vestibular Input.- Inputs from Precerebellar Reticular Nuclei.- Inputs from the Pontine Nuclei.- Inputs from the Inferior Olivary Nuclei.- Circuitry of the Cerebellar Cortex.- Anatomy.- Electrophysiology.- Efferent Pathways of the Cerebellum.- Projections to the Cerebellar Nuclei.- Projections to the Vestibular Nuclei.- Efferent Pathways of the Cerebellar Nuclei.- Electrophysiological Studies of the Cerebellum.- Background Levels of Discharge.- Afferent Input to the Cerebellar Cortex.- Afferent Input to the Cerebellar Nuclei.- Somatotopy.- Anaesthetised.- Awake.- Activity of Cerebellar Neurones during Active Movement.- Initiation and Control of Rapid Movements.- Relation of Discharge to Movement Parameters.- Relationship of Cerebellar Firing to Activity in Antagonist Muscles.- Activity of Cerebellar Neurones during Slow Movements.- Role of Cerebellum in Learning New Movements.- Limb Movements.- Vestibular-ocular Reflex.- Visually Triggered Movements.- Effects of Cerebellar Lesions.- Cerebellectomy in Cats and Dogs.- Cerebellectomy in Primates.- Reversible Cooling of Cerebellar Nuclei.- Electrical Stimulation of the Cerebellum.- Studies of Cerebellar Dysfunction in Man.- Clinical Symptoms.- Hypotonus.- Inco-ordination.- Physiological Investigations of Cerebellar Patients.- Stretch Reflexes.- Ballistic Limb Movements.- Slow Movements.- Complex Movements about More than One Joint.- Posture.- Theories of Cerebellar Function.- Cerebellum as a Timing Device.- Cerebellum as a Learning Device.- Cerebellum as Co-ordinator.- 10. The Basal Ganglia.- Anatomy.- Input-Output Connections of the Basal Ganglia.- Cortex-Basal Ganglia-Cortex Loop.- Motor Loop.- Complex Loop.- Other Outputs of the Basal Ganglia.- Strio-nigro-striatal and Strio-nigro-thalamic Loops.- GPi-Subthalamic Nucleus-GPe Loop.- Cytology and Pharmacology of Basal Ganglia Connections.- Electrophysiological Recordings from Behaving Animals.- Resting Discharge.- Relationship of Discharge to Movement.- Movement Related Cells: Somatotopy.- Movement Related Cells: Timing Relationships.- Movement Related Cells: Relationship to Movement Parameters.- Somatosensory Inputs to Basal Ganglia.- Context-dependent Cells.- Eye Movements and the SNpr.- Electrical Stimulation of the Basal Ganglia.- Effects of Lesions of the Basal Ganglia.- Globus Pallidus.- Substantia Nigra.- Subthalamic Nucleus.- Caudate and Putamen.- Summary.- Pathophysiology of Diseases of the Basal Ganglia in Man.- Parkinson’s Disease.- Physiological Studies in Parkinson’s Disease.- Rigidity.- Tremor.- Akinesia.- Postural Difficulties.- Chorea and Athetosis.- Torsion Dystonia.- Hemiballismus.