A person is lifting a dumbbell by flexing the elbow, bringing the dumbbell toward the shoulder. Which of the following statements BEST describes the cellular events that occur as the flexed elbow lowers the weight back down to the anatomical position

Option C

Explanation:

Options are

A. Repeated formation and reformation of cross-bridges until the muscle fibers shorten

B. Repeated formation and reformation of cross-bridges with some fiber shortening and some fiber lengthening

C. Repeated formation and reformation of cross-bridges that become farther apart as the muscle lengthens

D. Repeated formation and reformation of cross-bridges with no change in muscle length

Solutions

When the dumbbell is pushed towards the shoulder, the muscles at the elbow contracts due to the cross bridge cycling between actin and myosin resulting into shortening of sarcomere. At cellular level, the structure of sarcomere looks like a man holding and pulling something. Here myosin pulls the thin filaments of actin towards their center thereby shortening the sarcomere and causing contraction. The repeated action of actin and myosin is called as cross bridge cycling and as the muscle is released the cross-bridge moves far apart.

Hence, option C is correct

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