Question

You have a strange disorder in which both myosin and actin do not attach to the z-disk. Discuss the structure of the sarcomere and whether this disorder will influence the development of muscle tension. Defend your answer.

Answer 1

A sarcomere is the complicated unit of striated muscle tissue. It is the repeating unit between two Z lines.

Muscle fiber lined by the plasma membrane called sarcolemma enclosing the sarcoplasm.A charesteristic feature of muscle fiber is the presence of large numeber of parallely arranged filaments in the sarcoplasm called myofilaments or myofibrils.Each myofibril has alternate dark and white bands on it.A detailed study of the myofibril has established that the striated appearance is due to the distribution pattern of two important protein - Actin and Myosin.The light band contain actin and is called I band or isotropic band,whereas the dark band called A band or anisotropic band contains myosin.Both the proteis are arranged as rod like structures, parallel to each other and also to the longitudinal axis of myofibrils. Actin filaments are thinner as compared to myosin filaments, hence are commonly called thin and thick filaments respectivly. In the center of each I band is an elastic fiber called Z line which bisects it.The thin filaments are firmly attached to the Z line.The thick filaments in the A band are also held together in the middle of this band by a thin fibrous membrane called M line. The A and I bands are arranged alternatively throughout the lenghth of myofibrils.The portion of myofibril between two successive Z lines is considered as the functional unit of contracion and is called as sarcomere.In a resting state,the edges of thin filaments on either sides of the thick filaments partially overlap the free ends of thick filaments leaving the cenral part of the thick filaments.this central part of the thick filament, not overlaped by thin filaments is called the H zone.