Question 1

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

Accepted Answer

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

Question 2

A patient presents with muscle weakness and drooping eyelids. Laboratory tests reveal antibodies against acetylcholine receptors. Which process is most directly impaired?

Accepted Answer

Generation of end plate potential at the neuromuscular junction

Question 3

Which connective tissue sheath directly surrounds individual muscle fibers?

Accepted Answer

Endomysium

Question 4

During the sliding filament model of contraction, what happens to the length of the A band?

Accepted Answer

It remains unchanged.

Question 5

Which of the following is the correct sequence of events in excitation-contraction (E-C) coupling?

Accepted Answer

Action potential travels along sarcolemma $$\rightarrow T $$tubules $$\rightarrow Ca$^{2+}$$ released from SR $$\rightarrow$$ cross bridge formation

Question 6

Which protein binds calcium ions to initiate the removal of tropomyosin from actin’s binding sites during muscle contraction?

Accepted Answer

Troponin

Question 7

A toxin blocks voltage-gated Na$$^+$$ channels on the sarcolemma. What is the most immediate effect on muscle contraction?

Accepted Answer

Action potentials cannot propagate, preventing muscle contraction.

Question 8

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 9

Which of the following is a unique characteristic of cardiac muscle compared to skeletal and smooth muscle?

Accepted Answer

Branching chains of cells with intercalated discs

Question 10

Which event directly triggers the release of acetylcholine (ACh) from the axon terminal into the synaptic cleft?

Accepted Answer

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

Question 11

Which of the following best describes the function of the Na$$^+/K$^+$$ pump during repolarization of the muscle fiber?

Accepted Answer

It restores ionic conditions by pumping Na$$^+$$ out and K$$^+ in.$$

Question 12

Which of the following is true regarding the cross bridge cycle in skeletal muscle contraction?

Accepted Answer

ATP binding to myosin causes cross bridge detachment from actin.

Question 13

Which of the following best explains why skeletal muscle fibers are multinucleated?

Accepted Answer

They are formed by the fusion of multiple myoblasts during development.

Question 14

Which of the following is a function of the protein titin in the sarcomere?

Accepted Answer

It helps the muscle fiber recoil after being stretched.

Question 15

A drug that inhibits acetylcholinesterase would have what effect on muscle contraction?

Accepted Answer

Prolonged muscle contraction due to continued presence of ACh

Question 16

Which of the following best describes the difference between direct and indirect muscle attachments?

Accepted Answer

Direct attachments involve the epimysium fusing to the periosteum, while indirect attachments use tendons or aponeuroses.

Question 17

Which of the following is the correct order of connective tissue sheaths from outermost to innermost in a skeletal muscle?

Accepted Answer

Epimysium $$\rightarrow$$ Perimysium $$\rightarrow$$ Endomysium

Question 18

Which of the following events occurs first during the generation of an action potential in a muscle fiber?

Accepted Answer

End plate potential is generated by Na$$^+$$ influx through chemically gated channels.

Question 19

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

Accepted Answer

Excitability, contractility, extensibility, and elasticity

Question 20

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

Accepted Answer

They conduct action potentials deep into the muscle fiber to trigger Ca$$^{2+}$$ release.

Muscle Tissue and Contraction: Structure, Function, and Mechanisms

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