Chapter 19 - Contractile Systems

Abstract

Mammals have four cell types specialized for contraction—namely, skeletal muscle, cardiac muscle, smooth muscle, and myoepithelial cells. This chapter discusses muscle, an actin or myosin filament system, and cilia, a microtubule or dynein system. Motility usually requires two classes of protein, cytoskeletal and motor. The ability of a cell to hold or to change shape and to move organelles within it depends on the existence of a cytoskeleton comprising actin filaments, microtubules, and intermediate filaments capable of transmitting force. Actin filaments and microtubules contain predominantly actin and tubulin respectively. Intermediate filaments are structural proteins not directly involved in motion. The most abundant of these in muscle cells is desmin. Actin, tubulin and several of the intermediate filament proteins are found in all cells. The chapter describes the mechanism of muscle contraction. The mechanism of contraction is reflected in the sliding filament model and the cross-bridge hypothesis. Regulation of smooth and cardiac muscle, inherited diseases of muscle are discussed in the chapter.