Muscle Contraction and Relaxation

What triggers the release of calcium ions from the sarcoplasmic reticulum?

• ATP

• Acetylcholine

• Myosin

• Tropomyosin

Where are calcium ions stored in a resting muscle fiber?

• Cytosol

• Motor end plate

• Sarcoplasmic reticulum

• Neuromuscular junction

What is the role of the calcium pump in the sarcoplasmic reticulum?

• Transport calcium ions into the cytosol

• Actively transport calcium ions back into the sarcoplasmic reticulum

• Block myosin binding

• Synthesize ATP

What prevents myosin from binding to actin at rest?

• Acetylcholine

• Troponin-tropomyosin complex

• Calcium ions

• ATP

What happens when calcium binds to troponin?

• Tropomyosin blocks myosin binding

• Troponin changes shape, exposing actin binding sites

• ATP is hydrolyzed

• The sarcomere relaxes

What enzyme is found in myosin heads?

• Calcium ATPase

• ATPase

• Acetylcholinesterase

• Phosphatase

What is the role of ATPase in muscle contraction?

• Catalyzes ATP breakdown for energy

• Pumps calcium into the cytosol

• Stimulates acetylcholine release

• Blocks actin binding sites

What causes the sarcomere to shorten during contraction?

• Sarcoplasmic reticulum collapses

• Actin and myosin slide past each other

• Calcium ions detach from troponin

• ATP detaches from myosin

What happens to the H zone during contraction?

• It widens

• It narrows

• It stays the same

• It disappears

Which part of the sarcomere moves closer together during contraction?

• Z lines

• H zones

• M lines

• I bands