Muscle System 2: Muscle Contraction

Which statement best describes the sarcomere during contraction?

• It stays constant between Z-lines

• It lengthens toward the I-band

• It shortens as Z-lines move closer

• It lengthens as Z-lines separate

Where are actin and myosin filaments attached within a muscle fiber?

• To the H-band edges

• To Z-lines at each end

• To the M-line at each end

• To the A band borders

Which structure is located at the center of a sarcomere?

• H-band containing actin

• I-band overlapping actin

• M-line within myosin

• Z-line anchoring actin

What immediate event begins muscle fiber contraction?

• ATP diffuses to actin

• Calcium forms the Z-line

• Nerve impulses reach fibers

• Myosin splits into heads

During the sliding filament mechanism, what do myosin heads do?

• Detach from actin and elongate the I-band

• Detach from actin and push Z-lines apart

• Attach to actin and pull it inward

• Attach to myosin and widen the H-band

Match each term to its role in muscle contraction.

• Central line toward which filaments pull

• M-line

• Anchor point at sarcomere ends

• Actin

• Rounded extensions forming cross-bridges

• Myosin heads

• Twisted filaments pulled during contraction

• Z-line

Which changes occur as a muscle fiber shortens? Select all that apply.

• Myosin heads pull on actin

• I-band expands outward

• Sarcomere becomes shorter overall

• Z-lines move closer together

What provides the energy to power the sliding filament cycle?

• Lactic acid

• Oxygen gas

• Glucose chains

• ATP molecules

In the contraction cycle diagram, which event happens immediately after Ca2+ binds to troponin and shifts tropomyosin off the actin binding sites?

• Myosin releases ADP and Pi

• Myosin forms a cross-bridge

• ATP binds to myosin head

• Actin slides back to resting

Which pair correctly matches the molecule with its role shown in the diagram?

• Activates the myosin head

• ATP-->ADP + Pi

• Binds Ca2+ to expose actin

• New ATP attaches

• Cross bridge detaches

• Troponin

• Blocks actin binding sites at rest

• Tropomyosin