Question 1

Which of the following best describes the function of the sarcoplasmic reticulum (SR) in skeletal muscle fibers?

Accepted Answer

It stores and releases calcium ions ($$Ca^{2+}) $$necessary for muscle contraction.

Question 2

A patient presents with muscle weakness and drooping eyelids. Laboratory tests reveal antibodies against acetylcholine (ACh) receptors. Which disease is most likely responsible for these symptoms?

Accepted Answer

Myasthenia gravis

Question 3

During the cross bridge cycle, what event directly causes the detachment of the myosin head from actin?

Accepted Answer

Binding of ATP to the myosin head

Question 4

Which of the following is TRUE regarding the difference between isotonic and isometric muscle contractions?

Accepted Answer

Isotonic contractions result in muscle shortening, while isometric contractions do not change muscle length.

Question 5

A muscle fiber is stimulated so rapidly that it does not relax at all between stimuli, resulting in a smooth, sustained contraction. What is this phenomenon called?

Accepted Answer

Fused (complete) tetanus

Question 6

Which of the following best explains why rigor mortis occurs after death?

Accepted Answer

ATP is no longer produced, so myosin heads cannot detach from actin.

Question 7

Which of the following is the correct sequence of events for skeletal muscle contraction?

Accepted Answer

Action potential arrives at neuromuscular junction → ACh released → Sarcolemma depolarizes → Calcium released from SR → Cross bridge cycling

Question 8

Which of the following muscle fiber types is best suited for endurance activities such as marathon running?

Accepted Answer

Slow oxidative fibers

Question 9

A muscle is stretched to 120% of its resting length and then stimulated maximally. According to the length-tension relationship, what will happen to the force of contraction?

Accepted Answer

The force will be less than at optimal resting length.

Question 10

Which of the following best describes the role of creatine phosphate (CP) in muscle contraction?

Accepted Answer

It donates a phosphate group to ADP to rapidly regenerate ATP.

Question 11

A patient with Duchenne muscular dystrophy (DMD) has a mutation in the gene for dystrophin. What is the primary consequence of this mutation at the cellular level?

Accepted Answer

The sarcolemma becomes unstable and tears easily, allowing excess $$Ca^{2+}$$ entry.

Question 12

Which of the following is a function of muscle tone in the body?

Accepted Answer

It keeps muscles firm, healthy, and ready to respond.

Question 13

Which of the following best explains why fast glycolytic fibers fatigue more quickly than slow oxidative fibers?

Accepted Answer

They rely primarily on anaerobic glycolysis, which produces less ATP per glucose molecule.

Question 14

During a biceps curl, the biceps brachii shortens as it lifts a weight. What type of contraction is this?

Accepted Answer

Concentric isotonic contraction

Question 15

Which of the following statements about the neuromuscular junction is correct?

Accepted Answer

Acetylcholine (ACh) is released from the axon terminal and binds to receptors on the sarcolemma.

Question 16

Which of the following is the main source of ATP during prolonged, moderate-intensity exercise?

Accepted Answer

Aerobic respiration of glucose and fatty acids

Question 17

A muscle fiber is unable to contract despite continued stimulation. Which of the following is the most likely explanation?

Accepted Answer

The muscle fiber is experiencing fatigue due to ionic imbalances and increased inorganic phosphate.

Question 18

Which of the following best describes the 'size principle' of motor unit recruitment?

Accepted Answer

Smaller motor units are recruited first, followed by larger ones as stimulus intensity increases.

Question 19

Which of the following is a characteristic shared by all three types of muscle tissue (skeletal, cardiac, and smooth)?

Accepted Answer

Excitability (responsiveness) to stimuli

Question 20

Which of the following would most likely increase the force of skeletal muscle contraction?

Accepted Answer

Increasing the frequency of stimulation and recruiting more motor units

Chapter 9: Muscles and Muscle Tissue – Study Guide

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