Final answer:
In a sarcomere, thick filaments are linked together by proteins of the M line.
Step-by-step explanation:
Thick filaments are linked laterally by proteins of the M line. In muscle cells, sarcomeres are the basic functional units of a myofibril and are important for muscle contraction. Within a sarcomere, the A band is the region that contains overlapping thick and thin filaments. At the center of the A band lies the H zone which is a lighter area where the thick (myosin) filaments alone are found. The 'M line' runs down the center of the H zone and is where accessory proteins connect the thick filaments laterally, helping to maintain the structural integrity of the sarcomere during muscle contraction.
The Z line marks the boundary of a sarcomere and the I band is a lighter region made primarily of thin (actin) filaments. The A band's length remains constant during muscle contraction, while the I band shortens as the sarcomere contracts. The Z lines move closer together during contraction, reducing the distance between them.