Muscle Contraction-Ms J-AI

What is the contractile unit of a muscle called?

• Myofibril

• Sarcomere

• Myofilament

• Fascicle

Which protein is found in the thick filaments of muscle fibers?

• Actin

• Myosin

• Tropomyosin

• Troponin

What blocks the myosin binding sites on actin when a muscle fiber is relaxed?

• Calcium

• Troponin

• Myomesin

• Tropomyosin

What is the role of calcium ions in muscle contraction?

• They prevent the release of acetylcholine.

• They block myosin binding sites on actin.

• They bind to troponin, changing its shape.

• They form cross bridges between actin and myosin.

Where are calcium ions stored within the muscle cell?

• T tubules

• Neuromuscular junction

• Sarcolemma

• Sarcoplasmic reticulum

What initiates the action potential in a muscle cell?

• The depletion of ATP

• A signal from the nervous system

• The binding of calcium to troponin

• The release of myosin

What happens during depolarization of a muscle cell?

• Potassium ions enter the cell.

• Sodium ions enter the cell.

• Calcium ions are released from the sarcoplasmic reticulum.

• Sodium ions leave the cell.

What is the function of acetylcholinesterase in the synaptic cleft?

• It releases acetylcholine.

• It opens sodium channels.

• It binds calcium ions.

• It breaks down acetylcholine.

What is the role of T tubules in muscle contraction?

• They help signals reach every region of the muscle cell.

• They release acetylcholine.

• They bind to myosin heads.

• They store calcium ions.

What is the result of the sliding filament model of contraction?

• The muscle cell shortens.

• The sarcomere remains the same length.

• The muscle fiber lengthens.

• Calcium ions are depleted.