MEDICAL PHYSIOLOGY

Detailed explanation-1: -The giant protein titin (connectin) extends from the Z-line of the sarcomere, where it binds to the thick filament (myosin) system, to the M-band, where it is thought to interact with the thick filaments. Titin (and its splice isoforms) is the biggest single highly elasticated protein found in nature.

Detailed explanation-2: -The Z-band (Z-line, Z-disc) defines the boundary of the sarcomere in striated muscle and bisects the I-band of neighbouring sarcomeres (Fig. 1a) [1].

Detailed explanation-3: -The actin filaments are attached at their plus ends to the Z disc, which includes the crosslinking protein -actinin. The myosin filaments are anchored at the M line in the middle of the sarcomere.

Detailed explanation-4: -A sarcomere is defined as the distance between the Z-lines. The Z-lines are pulled closer together during contraction and move further apart during relaxation. The Z-lines are closer during contraction because actin and myosin interaction generates cross-bridges, which slide the myofilaments over each other.