Muscle Contraction Mechanisms

In a relaxed muscle, actin and myosin myofilaments are aligned side by side, with the H zones and I band at their widest. During contraction, actin and myosin interact, pulling actin towards the center of each myosin myofilament, causing sarcomeres to shorten. In a fully contracted muscle, actin myofilaments overlap, H zones disappear, and the I band narrows significantly.

What is the arrangement of actin and myosin myofilaments in a relaxed muscle?

• They are completely separated.

• They lie side by side.

• They are intertwined.

• They form a spiral structure.

What happens to the actin myofilaments during muscle contraction?

• They are pulled toward the center of the myosin.

• They dissolve.

• They remain stationary.

• They are pushed away from the myosin.

What is the result of the interaction between actin and myosin myofilaments during contraction?

• The muscle becomes rigid.

• The sarcomeres shorten.

• The myofilaments break apart.

• The muscle elongates.

In a fully contracted muscle, what happens to the H zones?

• They expand.

• They disappear.

• They double in size.

• They become more prominent.

What change occurs to the I band in a fully contracted muscle?

• It disappears completely.

• It becomes wider.

• It remains unchanged.

• It becomes very narrow.