Final answer:
Actin and myosin are proteins involved in muscle contraction. Nebulin helps maintain the length of thin filaments, and titin acts as a molecular spring in muscle cells.
Step-by-step explanation:
Actin is a protein that forms chains and is the primary component of microfilaments. In muscle cells, actin forms thin filaments and is responsible for muscle contraction.
Myosin is a protein that interacts with actin to cause muscle contraction. It has thick filaments that slide past actin filaments, resulting in muscle contraction.
Nebulin is a protein that plays a role in the structure and regulation of muscle filaments. It is found in thin filaments and helps maintain their proper length.
Titin is a protein that acts as a molecular spring in muscle cells. It helps to stabilize and position the myosin and actin filaments during muscle contraction.