Skeletal muscles are stimulated to contract by nerves and act as effectors: Practice Questions

In the ultrastructure of a myofibril, which region contains only the thick myosin filaments and becomes narrower during muscle contraction?

Which of the following occurs immediately after calcium ions are released from the sarcoplasmic reticulum into the myofibrils?

What occurs during the recovery stroke of the myosin head in the sliding filament theory?

Which of the following describes the correct orientation of muscles acting against an incompressible skeleton to allow movement in opposite directions?

A researcher is studying the rate of muscle fatigue in human volunteers. If a volunteer performs repeated muscular contractions at high intensity, what is the primary role of phosphocreatine in the first few seconds of this activity?

In the sliding filament theory of muscle contraction, describe the specific role of ATP hydrolysis by the myosin head in the cycle of cross-bridge formation.

In skeletal muscle contraction, describe the interaction between tropomyosin and the myosin-binding sites on actin filaments when calcium ion concentration in the sarcoplasm increases.

Compare the metabolic adaptations of slow-twitch and fast-twitch muscle fibres, specifically focusing on how the concentration of myoglobin and phosphocreatine relates to their respective functions as effectors.

A student used an optical microscope to examine a transverse section of a skeletal muscle. The student observed different types of muscle fibres and the arrangement of myofibrils.

(a) Describe two microscopic features of slow-twitch muscle fibres that distinguish them from fast-twitch fibres, and explain how these features adapt them for aerobic respiration. (3 points)
(b) During a single muscle contraction, the length of the I-band and H-zone decreases, but the A-band remains constant. Use your knowledge of the sliding filament theory to explain these observations. (2 points)