During the contraction phase of a muscle twitch,
A. acetylcholine stimulates the pre-synaptic terminal.
B. sodium ions diffuse into the muscle fiber.
C. actin-myosin cross-bridges form.
D. calcium ions are transported back to the sarcoplasmic reticulum.
E. the action potential travels down the T tubule.
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Question 2) A drug that interferes with the active transport of calcium ions from the sarcoplasm back into the sarcoplasmic reticulum would result in
A. relaxation of the muscle fiber.
B. contraction with no relaxation.
C. muscle hypertrophy.
D. fibrosis of the muscle.
E. an imbalance of blood calcium.
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Question 3) The time between application of the stimulus to a motor neuron and the beginning of contraction is called the _____ phase.
A. contraction
B. relaxation
C. latent or lag
D. refractory
E. threshold
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Question 4) Which of the following events occurs during the lag phase of a muscle twitch?
A. Muscle fibers shorten.
B. Cross-bridges form, move, release, and reform many times.
C. The action potential is propagated from presynaptic to postsynaptic membrane.
D. Calcium is pumped back into the sarcoplasmic reticulum.
E. All of these events occur in the lag phase.
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Question 5) In excitation-contraction coupling,
A. calcium ions must bind with myosin to expose active sites on actin.
B. myosin heads bind to exposed active sites on actin.
C. cross-bridges form between myosin heads and calcium ions.
D. movement of the troponin-tropomyosin complex causes actin myofilaments to slide.
E. ATP binds to actin myofilaments.
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Question 6) When the myosin head flexes into a bend, pulling the actin filament along with it, this is called the
A. action reaction.
B. power stroke.
C. recovery stroke.
D. muscle tone.
E. action potential.
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Question 7) In order for muscle relaxation to occur,
A. calcium ions must be transported to troponin.
B. power strokes slow down.
C. the active sites on actin must be blocked.
D. sodium ions must be actively transported to troponin.
E. the active sites on myosin must be uncovered.
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Question 8) One ATP molecule is required for
A. formation of the cross-bridge.
B. movement of the cross-bridge.
C. release of the cross-bridge.
D. formation of the cross-bridge and for movement of the cross-bridge.
E. formation of the cross-bridge, for movement of the cross-bridge, and for release of the cross-bridge.
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Question 9) Arrange these structures as they participate in excitation-contraction.
A. T tubules, sarcolemma, calcium ions, sarcoplasmic reticulum
B. calcium ions, T tubules, sarcolemma, sarcoplasmic reticulum
C. sarcolemma, T tubules, sarcoplasmic reticulum, calcium ions
D. sarcoplasmic reticulum, calcium ions, T tubules, sarcolemma
E. sarcolemma, sarcoplasmic reticulum, calcium ions, T tubules
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Question 10) The sarcoplasmic reticulum
A. stores calcium ions.
B. shortens during muscle contraction.
C. transmits nerve impulses to the myofibrils.
D. connects adjacent sarcomeres.
E. covers the muscle fiber.
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