Main description:

R. B. Stein Department of Physiology, University of Alberta, Edmonton, Canada The impetus for this volume and the conference that gave rise to it was the feeling that studies on motor control had reached a turning point. In recent years, studies on motor units and muscle receptors have become increasingly detailed. Attempts to integrate these studies into quantitative models for the spinal control of posture have appeared and preliminary attempts have been made to include the most direct supraspinal pathways into these models (see for example the chapters by Nashner and Melvill Jones et al. in this volume). Thus, we felt that the time was ripe to summarize these developments in a way which might be useful not only to basic medical scientists, but also to clinicians dealing with disorders of motor control, and to bioengineers attempting to build devices to assist or replace normal control. Over the past few years, computer methods have also made possible increasingly detailed studies of mammalian locomotion, and improved physiological and pharmacological studies have appeared. There seems to be almost universal agreement now that the patterns for locomotion are generated in the spinal cord, and that they can be generated with little, if any, phasic sensory information (see chapters by Grillner and Miller et al. ). This concludes a long controversy on whether chains of reflexes or central circuits generate stepping patterns. The nature of the pattern generators in mammals remains obscure, but invertebrate studies on locomotion have recently made striking advances.

Contents:

I: Motor Units and Muscle Spindles.- Demand and Accomplishment in Voluntary Movement.- Motoneurone Properties and Motor Control.- Functional Specialization in the Motor Unit Population of Cat Medial Gastrocnemius Muscle.- Somatotopic Connectivity or Species Connectivity?.- Physiological Estimates of the Numbers and Sizes of Motor Units in Man.- Contractile and Electrical Properties of Normal and Modified Human Motor Units.- Crustacean Motor Units.- Skeletomotor and Fusimotor Organization in Amphibians.- Evidence for Common Innervation of Bag and Chain Muscle Fibres in Cat Spindles.- Systems Approach to the Study of Muscle Spindles.- Non-Linear Behaviour of Spindle Receptors.- Discussion Summary.- Discussion Summary.- Discussion Papers.- A Third Mode of Repetitive Firing: Self-Regenerative Firing Due to Large Delayed Depolarizations.- Fatigability of Medial Gastrocnemius Motor Units in the Cat.- Motor Fields of Precentral Cells Elicited by Operant Reinforcement of Unit Activity.- Neck Muscle and Extraocular Receptors and Their Relationship to the Tectospinal Tract.- II: Control of Posture.- Postural Adaptation. The Nature of Adaptive Mechanisms in the Human Motor System.- The Significance of Intramuscular Receptors in Load Compensation During Voluntary Contractions in Man.- A Critique of the Hypothesis that the Spindle Secondary Endings Contribute Excitation to the Stretch Reflex.- The Stretch Reflex Response to Movement of the Human Elbow Joint.- The Continuity of Movements.- Postural Control: A Quantitative Study of Nervous System Functions in the Dog.- Vestibular and Reflex Control of Normal Standing.- A Cerebello-Thalamo-Cortical Pathway Controlling Fusimotor Activity.- The Supplementary Motor Area - A Control System for Posture ?.- Loading Reflexes During Two Types of Voluntary Muscle Contractions.- Control of Postural Reactions in Man: The Initiation of Gait.- Discussion Summary.- Discussion Summary.- Discussion Papers.- A Consideration of Stretch and Vibration Data in Relation to the Tonic Stretch Reflex.- Reflex and Non-Reflex Stiffness of Soleus Muscle in the Cat.- Effects of Secondary Muscle Spindle Afferent Discharge on Extensor Motoneurones in the Decerebrate Cat.- The Bases of Tremor During a Maintained Posture.- Compensation of Postural Control by Squirrel Monkeys Following Dorsal Column Lesions.- Proposal for Mode of Action of Anticholinergic Drugs Used in Parkinson's Disease.- III: Control of Locomotion.- Control of Motor Output.- Neuronal Organization and Ontogeny in the Lobster Swimmeret System.- Bursting Mechanisms in Molluskan Locomotion.- Crustacean Walking.- Nervous Control of Walking in the Cockroach.- Locomotion in the Spinal Cat.- Time Constraints for Inter-Limb Co-ordination in the Cat During Unrestrained Locomotion.- The Function of Long Propriospinal Pathways in the Co-ordination of Quadrupedal Stepping in the Cat.- Eighth Nerve Contributions to the Synthesis of Locomotor Control.- EMG of Locomotion in Gorilla and Man.- Discussion Summary.- Discussion Summary.- Discussion Papers.- The Relationship of Interlimb Phase to Oscillator Activity Gradients in Crayfish.- Gastrocnemius Muscle Activity in Human Locomotion.- Contributors.