Question 1

Which of the following best describes the role of the protein dystrophin in skeletal muscle fibers?

Accepted Answer

It links thin filaments to proteins of the sarcolemma, stabilizing the muscle fiber.

Question 2

A patient presents with muscle weakness, drooping eyelids, and difficulty swallowing. Laboratory tests reveal antibodies against acetylcholine receptors. Which disease is most likely responsible, and what is the underlying mechanism?

Accepted Answer

Myasthenia Gravis; autoimmune destruction of acetylcholine receptors at the neuromuscular junction.

Question 3

During a muscle contraction, which of the following events occurs according to the sliding filament model?

Accepted Answer

Thin filaments slide past thick filaments, increasing their overlap.

Question 4

Which of the following best explains why ATP is required for both the detachment of myosin heads from actin and the active transport of calcium ions back into the sarcoplasmic reticulum?

Accepted Answer

ATP hydrolysis provides energy for both cross bridge detachment and calcium ion pumps.

Question 5

A sprinter uses which primary metabolic pathway for ATP production during a 10-second burst of maximal effort?

Accepted Answer

Direct phosphorylation of ADP by creatine phosphate: $$\mathrm{Creatine\;phosphate + ADP \rightarrow Creatine + ATP}$$

Question 6

Which of the following best describes the difference between isometric and isotonic muscle contractions?

Accepted Answer

Isotonic contractions move a load as muscle length changes; isometric contractions generate tension without changing muscle length.

Question 7

A muscle fiber is stimulated by a series of rapid, repeated stimuli. The resulting contractions increase in force and do not fully relax between stimuli, eventually fusing into a smooth, sustained contraction. What is this phenomenon called?

Accepted Answer

Fused (complete) tetanus

Question 8

Which of the following statements about smooth muscle contraction is correct?

Accepted Answer

Smooth muscle contraction is triggered when calcium binds to calmodulin, which activates myosin light chain kinase.

Question 9

A muscle is stretched to 150% of its resting length before stimulation. According to the length-tension relationship, what will happen to the force of contraction, and why?

Accepted Answer

Force decreases because thick and thin filaments do not overlap sufficiently for cross bridge formation.

Question 10

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

Accepted Answer

They rely primarily on anaerobic glycolysis, which produces less ATP per glucose and accumulates lactic acid.

Question 11

During the latent period of a muscle twitch, which of the following events occurs?

Accepted Answer

Excitation-contraction coupling is occurring, but no measurable tension is produced yet.

Question 12

Which of the following best describes the function of T tubules in skeletal muscle fibers?

Accepted Answer

They transmit action potentials deep into the muscle fiber, ensuring simultaneous contraction.

Question 13

A patient is unable to perform fine motor tasks, such as writing, due to a loss of small motor units. Which of the following best explains this deficit?

Accepted Answer

Small motor units allow for precise, fine movements because they innervate fewer muscle fibers.

Question 14

Which of the following is a unique feature of unitary (visceral) smooth muscle compared to multiunit smooth muscle?

Accepted Answer

It is electrically coupled by gap junctions and often exhibits spontaneous action potentials.

Question 15

Which of the following best explains the phenomenon of rigor mortis after death?

Accepted Answer

Lack of ATP prevents cross bridge detachment, so myosin remains bound to actin.

Question 16

Which of the following best describes the process of recruitment in skeletal muscle contraction?

Accepted Answer

Activating additional motor units to increase the force of contraction.

Question 17

Which of the following is a correct sequence of events at the neuromuscular junction leading to muscle fiber excitation?

Accepted Answer

Acetylcholine is released, binds to receptors, opens chemically gated Na+ channels, and generates an end plate potential.

Question 18

Which of the following best explains why smooth muscle can maintain contraction for long periods with little energy expenditure?

Accepted Answer

Myofilaments may latch together, and ATP consumption is low due to slower ATPase activity.

Question 19

A marathon runner is able to sustain muscle activity for hours. Which muscle fiber type is most responsible for this endurance, and what is its primary metabolic pathway?

Accepted Answer

Slow oxidative fibers; aerobic respiration

Question 20

Which of the following best describes the effect of increased frequency of stimulation on muscle tension, assuming all other factors are constant?

Accepted Answer

Muscle tension increases due to wave summation and can reach fused tetanus at high frequencies.

Muscle and Muscle Tissue: Structure, Function, and Physiology

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