A sarcomere shortens when ________.

1. a. thick filaments shorten
2. b. thin filaments shorten
3. c. both thick and thin filaments shorten
4. d. none of the above

Introduction: The skeletal muscles are the voluntary muscles which help in the movement of bones and other structures. The sarcomeres are the contractile units contained in the myofibrils that are connected from one end to the other end. The sliding-filament model explains about the muscle contraction with the help of the proteins, such as actin and myosin.

Reason for the correct statement:

Actin is a type of globular protein which is present mostly in the skeletal muscles of eukaryotes. It is the thin filaments that help to form the microfilaments. Myosin is a type of motor proteins which is present in the myofibrils of the muscle fibers. It is the thick filaments which play a major role in the muscle contraction by binding to the actin.

The sliding-filament model explains about the muscle contraction with the help of the proteins, such as actin and myosin. For the muscle contraction, neither myosin nor actin filaments alter their length. Also the myosin filaments will not alter their position. Instead, they mainly use the energy released by the ATP hydrolysis in order to move the thin filaments to the sarcomere center. When the thin filaments are pulled inward, the sarcomere ends are drawn close to each other. Thus, the sarcomere shortens.

Option d. is given as “none of the above”.

When the thin filaments are pulled inward, the sarcomere ends are drawn close to each other. Thus, the sarcomere shortens.

Hence, the correct answer is option d.

Reasons for the incorrect statements:

Option a...