56 - Contraction of Muscles

Abstract

This chapter discusses muscle structure in relation to contractility. The focus of the chapter is on the nature of the mechanochemical energy conversion. The chapter emphasizes largely on the relationships between muscle structure and function at the cellular and subcellular levels. The chapter discusses several related concepts, including the muscle mechanisms of force production and shortening, muscle energetics, and muscle metabolism. The muscle mechanisms of force production and shortening further discusses sliding filament theory, relationships among force, velocity and work, and energy utilization cross-bridge theory. Muscle structure is first developed in conjunction with mechanics, leading to the formulation of the sliding-filament theory. Muscle contractility continues with further characterization of the relationships among force, velocity, work, and energy utilization. The mechanism at the molecular level that is at the cross-bridge cycle is similarly developed, matching structural and biochemical knowledge with transient mechanical studies. The energy requirements of the cross-bridge cycle lead to presentation of energy use in intact muscle, which is considered in detail in muscle energetics. Energy use is then followed by a discussion of muscle metabolism and the route for synthesis of ATP necessary for contractile activity. The chapter discusses comparative muscle physiology and behavior of different fiber types. Smooth muscle is discussed in detail along with its regulation, mechanical properties, and energetics and contrasted to those of striated muscle.