Muscle cells are the contractile elements in the muscle tissue and are called muscle fibers since they are elongated. They are designed for movements, which is due to contractility of muscle fibers. Muscle cell are classified as skeletal muscle, smooth muscle, and cardiac muscle. Muscle cannot contract due to the damage of the motor pathways or inherent disease of muscle. The damage of motor pathways can be either at the level of central nervous system or at the level of peripheral nervous system. Disuse atrophy is the muscles which are not used for long times become thin and weak. Muscular ‘wasting’ (reduction in size) is a feature of lower motor neuron paralysis and generalized debility. In this chapter, short essay type questions are also provided.