Question 1

Which of the following best describes the main structural difference between skeletal and smooth muscle fibers?

Accepted Answer

Skeletal muscle fibers are multinucleated and striated, while smooth muscle fibers are uninucleated and lack striations.

Question 2

During skeletal muscle contraction, what is the role of the SERCA pump?

Accepted Answer

It actively transports calcium ions back into the sarcoplasmic reticulum, lowering cytoplasmic calcium and ending contraction.

Question 3

Which of the following best explains why fast twitch muscle fibers contract more rapidly than slow twitch fibers?

Accepted Answer

Fast twitch fibers contain fast myosin, which hydrolyzes ATP to ADP and $$P_i$$ more quickly, allowing faster myosin head cocking.

Question 4

A patient is experiencing muscle fatigue after prolonged low-intensity exercise. What is the most likely physiological cause?

Accepted Answer

Depletion of glycogen stores in the muscle fibers.

Question 5

Which of the following statements about the source of calcium in muscle contraction is correct?

Accepted Answer

Skeletal muscle contraction relies primarily on internal $$Ca^{2+}$$ from the sarcoplasmic reticulum, while smooth muscle contraction relies mostly on external $$Ca^{2+}$$ entering the cell.

Question 6

Which of the following best describes the function of troponin in skeletal muscle contraction?

Accepted Answer

Troponin binds $$Ca^{2+}$$, causing a conformational change that moves tropomyosin and exposes myosin binding sites on actin.

Question 7

A muscle is generating force but not shortening because the load is greater than the muscle tension. What type of twitch is this?

Accepted Answer

Isometric twitch

Question 8

Which of the following changes would you expect in skeletal muscle fibers after several weeks of high-intensity anaerobic exercise?

Accepted Answer

Increase in glycolytic enzymes and fiber diameter, decrease in mitochondria.

Question 9

Which of the following best explains the process of crossbridge cycling in skeletal muscle contraction?

Accepted Answer

Myosin heads bind to actin, perform a power stroke, release ADP and $$P_i$$, then bind ATP to detach and re-cock.

Question 10

A marathon runner’s muscles are adapted for endurance. Which muscle fiber characteristics would you expect to be most prominent?

Accepted Answer

High myoglobin content, many mitochondria, small fiber diameter, and dark color.

Question 11

Which of the following events directly terminates skeletal muscle contraction?

Accepted Answer

Active uptake of $$Ca^{2+}$$ into the sarcoplasmic reticulum by SERCA pumps.

Question 12

Which of the following is a key difference between the contraction mechanisms of skeletal and smooth muscle?

Accepted Answer

Smooth muscle contraction is regulated by phosphorylation of myosin light chains, while skeletal muscle contraction is regulated by troponin binding to $$Ca^{2+}.$$

Question 13

Which of the following best describes the role of tropomyosin in skeletal muscle contraction?

Accepted Answer

Tropomyosin blocks myosin binding sites on actin in the absence of $$Ca^{2+}.$$

Question 14

A weightlifter is performing a lift where the muscle shortens and the load is moved. Which type of muscle twitch is occurring?

Accepted Answer

Isotonic twitch

Question 15

Which of the following is true regarding the conversion of muscle fiber types with exercise?

Accepted Answer

Low intensity exercise can convert some glycolytic fibers into oxidative fibers.

Question 16

Which of the following best explains why smooth muscle can contract even though it lacks sarcomeres?

Accepted Answer

Actin and myosin in smooth muscle run parallel in several axes and connect to dense bodies, allowing contraction through crossbridge cycling.

Question 17

Which of the following would most likely occur in a muscle fiber after several weeks of low-intensity aerobic exercise?

Accepted Answer

Increase in the number and size of mitochondria, and an increase in capillary density.

Question 18

Which of the following is a correct sequence of events in excitation-contraction coupling in skeletal muscle?

Accepted Answer

Motor neuron action potential → End plate potential → Increase in $$Ca^{2+}$$ → Troponin/tropomyosin conformational change → Crossbridge cycling

Question 19

Which of the following best describes the mechanism by which smooth muscle contraction is terminated?

Accepted Answer

Inactivation of myosin by phosphatases, which remove phosphate groups from myosin light chains.

Bio 2160 Ch.10

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