Actin is a protein that plays a crucial role in the structure and movement of cells. It forms long, thin filaments that are part of the cytoskeleton, which helps maintain the cell's shape and enables various cellular functions, such as division and motility. In addition to its structural role, actin is involved in muscle contraction. In muscle cells, actin filaments interact with another protein called myosin to facilitate movement. This interaction is essential for all types of muscle activity, including voluntary movements like walking and involuntary movements like the heartbeat.