The Structure and Growth of Muscle

This chapter summarizes the structure, development, and growth of skeletal muscles and their components. Muscles throughout the body of an animal have different compositions and structure due to the fact that they carry out different functions in vivo. Although the basic structure of the sarcomere, the fundamental functional unit of muscle contraction, is common to all skeletal muscles, there are many polymorphisms in the contractile proteins, and variations in the metabolism of the muscle cells, which act to fine-tune the properties of each muscle to their in vivo functions. At a higher level of organization, variations in the organization of muscle fibers into fascicles by intramuscular connective tissue are another functional difference between muscles. These natural and well-directed variations inevitably lead to variations in eating quality when muscles are consumed as meat. The development of muscle tissue from embryogenesis through postnatal growth and maturation is a multistage process coordinating myogenesis, adipogenesis, and fibrogenesis, and the subsequent growth of muscle, fat, and connective tissues. The signaling pathways, growth factors, nutritional factors, and environmental factors that together influence growth and development are outlined here.