Animal Movement

Animal Movement
Movement is an important characteristic of animals. Animal movement occurs in many forms in animal tissues, ranging from barely discernible streaming of cytoplasm to extensive movements of powerful striated muscles. Most animal movement depends on a single fundamental mechanism: contractile proteins, which can change their form to elongate or contract. This contractile machinery is always composed of ultrafine fibrils— fine filaments, striated fibrils, or tubular fibrils (microtubules)—arranged to contract when powered by ATP. By far the most important protein contractile system is the actomyosin system, composed of two proteins, actin and myosin. This is an almost universal biomechanical system found from protozoa to vertebrates; it performs a long list of diverse functional roles. Cilia and flagella, however, are composed of different proteins, and thus are exceptions to the rule. In this discussion we examine the three principal kinds of animal movement: ameboid, ciliary, and muscular.