Chapter 58 - The Contractile Machinery of Skeletal Muscle

Abstract

Skeletal muscle, like cardiac, is organized into repeating units of contractile proteins that are known as sarcomeres. This chapter describes the general features of this structural organization as well as properties of the molecular motor of the sarcomere, myosin, and its regulation. The motor domains of myosin (thick) filaments form cross-bridges that, via their cyclic interactions with actin (thin) filaments, use ATP to generate force and movement. These cross-bridge interactions result in a relative sliding of the actin and myosin filaments, leading to shortening of the sarcomere. The cyclic actin and myosin interactions are regulated by calcium binding to the troponin and complexes that interact with tropomyosin on the actin filaments. Cross-linking elements at the Z- and M-lines hold the sarcomeric structures in place, while scaffolding proteins provide elasticity and stability to the sarcomeres.