Question 1

Which of the following best describes the primary function of the sarcoplasmic reticulum in skeletal muscle fibers?

Accepted Answer

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

Question 2

A patient is diagnosed with a disorder that prevents the release of acetylcholine at the neuromuscular junction. Which step in muscle contraction will be directly affected?

Accepted Answer

Depolarization of the motor end plate will not occur, preventing the initiation of an action potential in the muscle fiber.

Question 3

During the sliding filament theory of muscle contraction, which event occurs immediately after ATP binds to the myosin head?

Accepted Answer

The myosin head detaches from actin (cross bridge detachment).

Question 4

Which of the following best explains why cardiac muscle cells can contract in a coordinated fashion without direct neural stimulation?

Accepted Answer

They are connected by gap junctions that allow rapid communication between cells.

Question 5

A muscle fiber is stimulated to contract, but the sarcomere does not shorten. Which of the following is the most likely explanation?

Accepted Answer

ATP is not available to detach the myosin head from actin, preventing the cross bridge cycle.

Question 6

Which connective tissue layer surrounds an entire muscle and separates it from surrounding tissues?

Accepted Answer

Epimysium

Question 7

A toxin blocks the reuptake of calcium ions into the sarcoplasmic reticulum. What is the most immediate effect on muscle contraction?

Accepted Answer

The muscle will remain contracted because calcium stays bound to troponin.

Question 8

Which of the following best describes the role of troponin in muscle contraction?

Accepted Answer

It binds calcium ions, causing a conformational change that moves tropomyosin and exposes binding sites on actin.

Question 9

A muscle is unable to maintain contraction and quickly fatigues. Which property of muscle is most likely compromised?

Accepted Answer

Endurance (related to the ability to generate ATP and sustain contraction)

Question 10

Which of the following equations correctly represents the hydrolysis of ATP during muscle contraction?

Accepted Answer

$$ATP + H_2O \rightarrow ADP + P_i + energy$$

Question 11

Which of the following best explains why skeletal muscle fibers appear striated under a microscope?

Accepted Answer

The regular arrangement of thick and thin filaments into sarcomeres creates a repeating pattern of light and dark bands.

Question 12

A patient presents with muscle weakness and is found to have a defect in the T-tubules. Which process is most directly impaired?

Accepted Answer

Transmission of the action potential into the interior of the muscle fiber.

Question 13

Which of the following statements about the motor unit is correct?

Accepted Answer

A motor unit consists of a single motor neuron and all the muscle fibers it innervates.

Question 14

Which of the following best describes the function of the perimysium?

Accepted Answer

It surrounds bundles of muscle fibers called fascicles.

Question 15

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

Accepted Answer

Continuous stimulation of the muscle fiber, leading to prolonged contraction.

Question 16

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

Accepted Answer

Action potential travels down T-tubule $$\rightarrow$$ calcium released from sarcoplasmic reticulum $$\rightarrow$$ calcium binds troponin $$\rightarrow$$ tropomyosin moves $$\rightarrow$$ myosin binds actin

Question 17

Which property allows muscle tissue to respond to a neural stimulus and generate an action potential?

Accepted Answer

Excitability

Question 18

A muscle is stretched beyond its normal resting length and then released. Which property of muscle allows it to return to its original length?

Accepted Answer

Elasticity

Question 19

Which of the following best explains why smooth muscle contraction is slower and more sustained than skeletal muscle contraction?

Accepted Answer

Smooth muscle lacks sarcomeres and contracts via a different mechanism involving dense bodies.

Question 20

A patient is unable to maintain posture and experiences frequent falls. Which function of skeletal muscle is most likely impaired?

Accepted Answer

Maintenance of posture

Muscle Tissue: Structure, Function, and Contraction Mechanisms

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