MEDICAL PHYSIOLOGY

Detailed explanation-1: -Titin is an extremely large protein (3000 kd), and single titin molecules extend from the M line to the Z disc. These long molecules of titin are thought to act like springs that keep the myosin filaments centered in the sarcomere and maintain the resting tension that allows a muscle to snap back if overextended.

Detailed explanation-2: -During contraction, the interaction of myosin heads with the actin filaments pulls the thin filaments toward the center of the sarcomere.

Detailed explanation-3: -There are three different types of myofilaments: thick, thin, and elastic filaments. Thick filaments consist primarily of a type of myosin, a motor protein – myosin II.

Detailed explanation-4: -As the actin is pulled, the filaments move approximately 10 nm toward the M line. This movement is called the power stroke, as it is the step at which force is produced. As the actin is pulled toward the M line, the sarcomere shortens and the muscle contracts.

Detailed explanation-5: -Thin myofilaments are 1 m long and 8 nm in diameter, consisting primarily of actin. Actin is a globular protein with a molecular weight of 43 kDa. Two F-actin strands twisted in a double helix form the backbone of the thin myofilament and possess a complementary binding site for the myosin globular head.