Chapter 21 Neuromuscular Strategies Underlying Ballistic Movements

Abstract

Publisher Summary The major goal of motor control research is to advance the understanding of the central nervous system (CNS) mechanisms that bring about movement diversity. Such diversity results from two sources of variation: (1) the design of musculoskeletal elements that participate in movement and (2) the way these elements are activated by the CNS. Conceptually, the simplest approach to understanding how a neuromuscular system might generate a specific type of movement is to begin by studying the individual properties of its various components—for example, the muscle fiber (MF), the motor unit (MU), and the motoneurons (MNs). Eventually, a picture begins to emerge showing how the distinctive components might function during movement. For example, skeletal muscles are composed of MFs that have different morphological (e.g., lengths, diameters, and tapering profiles), physiological, and biochemical (e.g., contraction speed and fatigability) properties. Each of these properties and their various combinations confer certain capabilities on the muscle. The assembly of individual MFs with different properties to form whole MUs and whole muscles and the activation of this assembly of usually heterogeneous MFs and MUs by the CNS, at both segmental and supra-segmental levels, are some of the important questions to be addressed. This approach has been applied with great success to the groups of muscles that are involved in the cyclical patterns of muscle activation that are driven by central pattern-generating circuits (e.g., chewing, scratching, and locomotion). In contrast, much less is known about muscle systems that are involved in ballistic movements. This chapter discusses the design of the various musculoskeletal and neural elements that participate in ballistic head retraction—the chief escape response in turtles.