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 $\mathrm{Ca^{2+}}$ ions, which are essential for triggering muscle contraction.

Question 2

A patient with Duchenne muscular dystrophy has a mutation affecting dystrophin. What is the primary consequence of this mutation at the cellular level?

Accepted Answer

The muscle cell membrane becomes fragile, leading to muscle fiber damage during contraction.

Question 3

During the sliding filament mechanism, what happens to the sarcomere as a whole when a muscle contracts?

Accepted Answer

The sarcomere shortens as Z discs move closer together.

Question 4

Which of the following is TRUE regarding the difference between skeletal and cardiac muscle?

Accepted Answer

Skeletal muscle is voluntary and attached to bones, while cardiac muscle is involuntary and found only in the heart.

Question 5

What is the function of myoglobin in skeletal muscle fibers?

Accepted Answer

It stores oxygen for use during muscle contraction.

Question 6

A muscle fiber is stimulated to contract. Which sequence of events correctly describes the role of $\mathrm{Ca^{2+}}$ in the cross-bridge cycle?

Accepted Answer

$\mathrm{Ca^{2+}}$ binds to troponin, causing tropomyosin to move and expose myosin-binding sites on actin.

Question 7

Which connective tissue layer surrounds an individual muscle fiber?

Accepted Answer

Endomysium

Question 8

A marathon runner is able to maintain posture for long periods. Which functional characteristic of muscle does this best illustrate?

Accepted Answer

Tonic contraction (maintaining posture)

Question 9

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 10

Which of the following statements about the T-tubules in skeletal muscle is correct?

Accepted Answer

They conduct action potentials deep into the muscle fiber, ensuring uniform contraction.

Question 11

A muscle cell is described as a syncytium. What does this mean?

Accepted Answer

It is a multinucleated cell formed by the fusion of many precursor cells.

Question 12

Which of the following best describes the difference between G-actin and F-actin?

Accepted Answer

G-actin is a globular monomer, while F-actin is a filamentous polymer formed by G-actin subunits.

Question 13

A patient is unable to generate forceful muscle contractions. Which of the following is most likely impaired?

Accepted Answer

The ability of myosin heads to form cross-bridges with actin.

Question 14

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

Accepted Answer

It provides elasticity and helps the muscle fiber recoil after being stretched.

Question 15

During muscle relaxation, which of the following events occurs?

Accepted Answer

Calcium ions are actively transported back into the sarcoplasmic reticulum.

Question 16

Which of the following best describes the role of ATP in the cross-bridge cycle?

Accepted Answer

ATP binds to myosin, causing it to detach from actin after the power stroke.

Question 17

A muscle fiber is observed under a microscope and shows alternating light and dark bands. What is the primary cause of this striation pattern?

Accepted Answer

The regular arrangement of actin and myosin filaments in sarcomeres.

Question 18

Which of the following best explains why only a small percentage of myosin heads are pulling at any one time during muscle contraction?

Accepted Answer

This allows for smooth, sustained contraction and prevents all cross-bridges from detaching simultaneously.

Question 19

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

Accepted Answer

The rapid transmission of action potentials into the muscle fiber interior.

Question 20

Which of the following is the correct order of structures from largest to smallest in a skeletal muscle?

Accepted Answer

Muscle, fascicle, muscle fiber, myofibril, myofilament

Cellular Physiology of Muscle: Structure and Function of Muscle Tissue

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