Of the three kingdoms of multicellular organisms, animals are by far the most active. Plants and fungi are sedentary, growing in one spot. If they move, it is by growth or as a result of being blown by the wind or carried along by moving water or animals. Some animals are also sedentary and passive movers, but the vast majority of animals exhibit locomotion. They actively move their body parts and actively move from place to place. Such movement has resulted in the active lifestyle we associate with animals-the running, swimming, flying, hopping, crawling, walking, and other motions that are employed to migrate, obtain food, flee from danger, and so on. All animal locomotion follows the same basic principle: muscles contract and work against an internal or external skeleton, which results in particular body parts being moved. For vertebrates, the skeleton is internal and is composed of bone and/or cartilage. The microscopic anatomy of skeletal muscles results in contractions that can generate significant force. The contracting of muscles is not random, but is under the control of the central nervous system.