Question 1

Which structure in a skeletal muscle fiber is functionally equivalent to the plasma membrane in a generalized cell?

Accepted Answer

Sarcolemma

Question 2

During the sliding filament theory of muscle contraction, which part of the sarcomere shortens?

Accepted Answer

I band

Question 3

If the sarcolemma of a muscle fiber is damaged, which of the following processes would be most directly affected?

Accepted Answer

Propagation of action potentials along the muscle fiber

Question 4

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

Accepted Answer

It stores and releases calcium ions ($$\mathrm{Ca$$^{2+}$$})$$

Question 5

A patient has a genetic defect that prevents the formation of dystrophin. Which of the following is the most likely consequence?

Accepted Answer

Uncontrolled muscle contractions due to loss of structural support

Question 6

Which of the following correctly matches the muscle structure to its organizational level?

Accepted Answer

Myocyte – cell

Question 7

At the neuromuscular junction, which event directly triggers the release of acetylcholine (ACh) from the presynaptic neuron?

Accepted Answer

Influx of $$\mathrm{Ca$$^{2+}$$}$$ into the axon terminal

Question 8

Which of the following best explains why the action potential at the neuromuscular junction is rapidly transmitted to the muscle fiber?

Accepted Answer

There is virtually no distance between the motor end plate and the sarcolemma

Question 9

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

Accepted Answer

ACh release → action potential in sarcolemma → calcium release from sarcoplasmic reticulum → contraction

Question 10

A researcher blocks all voltage-gated sodium channels in a muscle fiber. What is the most immediate effect on muscle function?

Accepted Answer

The muscle fiber cannot generate an action potential

Question 11

Which of the following best describes the relationship between a myofibril and a myocyte?

Accepted Answer

A myocyte contains many myofibrils

Question 12

Which of the following would most likely occur if the sarcoplasmic reticulum failed to reabsorb $$\mathrm{Ca$$^{2+}$$}$$ after contraction?

Accepted Answer

The muscle would remain contracted

Question 13

Which of the following is a direct result of acetylcholine binding to its receptor on the muscle fiber?

Accepted Answer

Depolarization of the sarcolemma due to sodium influx

Question 14

A muscle fiber is exposed to a toxin that prevents the breakdown of acetylcholine in the synaptic cleft. What is the most likely effect?

Accepted Answer

Continuous stimulation and possible muscle spasm

Question 15

Which of the following best describes the function of myofibrils within a muscle fiber?

Accepted Answer

They generate contractile force through the sliding of actin and myosin filaments

Question 16

A patient presents with muscle weakness. Laboratory tests reveal a defect in the voltage-gated calcium channels at the axon terminal of motor neurons. Which step in muscle contraction is most directly impaired?

Accepted Answer

Release of acetylcholine into the synaptic cleft

Question 17

Which of the following equations best represents the relationship between force ($$F$$), mass ($$m$$), and acceleration ($$a) as it $$applies to muscle contraction?

Accepted Answer

$$F = m 	imes a$$

Question 18

Which of the following is a correct analogy between a neuron and a muscle fiber?

Accepted Answer

The plasma membrane in a neuron is analogous to the sarcolemma in a muscle fiber

Question 19

A muscle fiber is unable to contract even though acetylcholine is released and binds to its receptors. Which of the following is the most likely explanation?

Accepted Answer

The sarcolemma lacks voltage-gated sodium channels

Question 20

Which of the following best explains why ATP is necessary for muscle contraction?

Accepted Answer

ATP is needed for the detachment of myosin heads from actin filaments

Skeletal Muscle: Cellular Structure and Function

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