Muscle systems refer to the groups of muscles in the body that work together to facilitate movement and maintain posture. There are three main types of muscle tissue: skeletal muscle, which is under voluntary control and helps with movement; smooth muscle, which is involuntary and found in organs; and cardiac muscle, which makes up the heart and is also involuntary. These muscle systems operate through contraction and relaxation, allowing the body to perform various activities. The nervous system plays a crucial role in signaling muscles to contract, enabling actions like walking, lifting, and even breathing. Proper functioning of these systems is essential for overall health and mobility.