Chapter 2 - Basics of Skeletal Muscle Function and Normal Physiology

Abstract

Skeletal muscle comprises approximately 45% of human body mass and has an essential role in metabolism and movement. It is a plastic tissue that adapts to use, disease, ageing, and malignancies. This chapter summarizes aspects of normal muscle development, growth, structure, proprioceptors, and muscle contraction. Muscle fibers are multinucleated and form from the fusion of postmitotic myoblasts. The regular, sarcomeric arrangement of proteins gives skeletal muscle its characteristic striated pattern. In contrast to cardiac muscle, skeletal muscles are composed of fibers with different biochemical and physiological properties, the proportions of which vary between muscles. Muscle has an extensive vascular network and all fibers are innervated by one nerve. However, the axon of the motor neuron is branched and innervates a number of fibers. The anterior horn cell, axon, and muscle fibers it innervates constitute a functional motor unit. The axon interacts with the muscle fiber at specialized regions known as neuromuscular junctions allowing an action potential to depolarize the muscle fiber membrane and induce the release of calcium, resulting in contraction.