When a muscle has been repeatedly contracting at a moderate intensity for an extended period of time (more than a few minutes), what is the primary source of ATP?
A. transfer of energy and phosphate from creatine phosphate to ADP
B. glycolysis
C. oxidative phosphorylation
D. breakdown of myosin
E. uptake of ATP from the blood plasma
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Question 2) In the first few seconds of skeletal muscle contraction, what is the main mechanism by which ATP is replenished?
A. Energy and phosphate are transferred from creatine phosphate to ADP.
B. Oxidative phosphorylation rapidly generates ATP from glucose.
C. Glycolysis produces ATP from glycogen.
D. Oxidation of fatty acids into ATP occurs in the mitochondria.
E. Myoglobin catalysis produces ATP.
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Question 3) The optimal length (Lo) of a skeletal muscle cell is:
A. the length at which the muscle can generate its maximum tetanic tension.
B. the shortest length the muscle can achieve while attached to bone, because the amount of overlap between thick and thin filaments is maximal then.
C. generally the length attained when the joint it crosses is fully extended.
D. the only length at which any tension can be generated by the muscle cell.
E. the length at which thin filaments from opposite sides of a sarcomere overlap.
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Question 4) How is the length of a skeletal muscle cell related to the force it can generate?
A. The tension in a skeletal muscle cell is greatest when contractions occur at either very short or very long lengths.
B. Skeletal muscle cells generate the same amount of force, regardless of their length.
C. The shorter a skeletal muscle cell is when it begins to contract, the stronger the force generation will be.
D. The longer a skeletal muscle cell is when it begins to contract, the stronger the force generation will be.
E. Skeletal muscle cells generate the most force when the contraction occurs at an intermediate length.
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Question 5) What is the best description of a tetanic contraction in a skeletal muscle cell?
A. A single action potential in the motor neuron causes a sustained contraction.
B. Multiple action potentials in the motor neuron cause a sustained contraction.
C. The action potential in the muscle cell is prolonged to last as long as the contraction.
D. Repeated action potentials from the motor neuron summate into a sustained depolarization of the motor end plate, causing a sustained contraction.
E. A very large amplitude action potential in the motor neuron causes a very strong contraction in the skeletal muscle cell.
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Question 6) Which of the following statements regarding skeletal muscle contraction is true?
A. During a lengthening contraction, the tension exerted by the muscle exceeds the load on the muscle.
B. In every isotonic muscle contraction, the length of the muscle remains constant.
C. During every muscle contraction, muscle fibers change length.
D. During every muscle contraction, tension is developed in the muscle.
E. Cross-bridges cycle faster during isometric contractions than during isotonic contractions.
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Question 7) During an isometric twitch in a skeletal muscle:
A. tension generated by the muscle always exceeds the load on the muscle.
B. tetanus occurs.
C. sarcomeres do not significantly shorten.
D. the whole muscle shortens.
E. H zones shorten.
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Question 8) Which of these occurs during an isometric contraction of a skeletal muscle?
A. The I bands shorten and the A bands stay the same length.
B. The thick and thin filaments slide past each other.
C. Sarcomere length does not change significantly.
D. The A bands shorten and the I bands stay the same length.
E. Cross-bridges lock onto actin, similar to what occurs in rigor mortis.
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Question 9) Myasthenia gravis is an autoimmune disease in which the immune system gradually destroys the receptors for acetylcholine at the neuromuscular junction.
Which of the following drugs might initially be useful in treating the symptoms of this disease?
A. a drug that inhibits acetylcholinesterase
B. a drug that inhibits release of acetylcholine
C. curare
D. atropine (a muscarinic acetylcholine receptor antagonist)
E. a nicotinic acetylcholine receptor antagonist
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Question 10) How does the chemical curare affect skeletal muscle function?
A. It activates an autoimmune disease that destroys myelin.
B. It blocks the action of acetylcholinesterase at the neuromuscular junction.
C. It is a muscarinic acetylcholine receptor antagonist that blocks synaptic transmission at the neuromuscular junction.
D. It is a nicotinic acetylcholine antagonist that blocks synaptic transmission at the neuromuscular junction.
E. It locks ligand-gated channels in the open state, leading to spastic contractions of muscle.
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