Q: A researcher measures the average muscle shortening during contraction and finds it to be approximately 30%. Which equation best represents the percentage of shortening if the original sarcomere length is $L_0$ and the contracted length is $L_c$?

$\frac{L_0 - L_c}{L_0} \times 100\%$

Question 1

Which of the following statements best describes the difference between skeletal and cardiac muscle cells?

Accepted Answer

Skeletal muscle cells are voluntary and striated, while cardiac muscle cells are involuntary and striated.

Question 2

A patient with muscular dystrophy is found to have a deficiency in dystrophin. What is the primary role of dystrophin in muscle cells?

Accepted Answer

It serves as a shock absorber anchoring the force generated by muscle contraction.

Question 3

Which of the following best explains why smooth muscle is able to contract for longer periods without fatigue compared to skeletal muscle?

Accepted Answer

Smooth muscle uses a slower cross-bridge cycling mechanism and is not striated.

Question 4

During muscle contraction, which event directly follows the release of Ca$^{2+}$ from the sarcoplasmic reticulum?

Accepted Answer

Troponin binds to Ca$^{2+}$, causing tropomyosin to move and expose the active site on actin.

Question 5

Which structure in a skeletal muscle cell is responsible for storing and releasing calcium ions during contraction?

Accepted Answer

Sarcoplasmic reticulum

Question 6

If a muscle cell is unable to produce ATP, which step in the cross-bridge cycle would be directly affected?

Accepted Answer

Myosin would not be able to detach from actin, resulting in rigor.

Question 7

Which of the following best describes the arrangement of myofilaments within a sarcomere?

Accepted Answer

Actin filaments are anchored at the Z disk and myosin filaments span the A band.

Question 8

A muscle fiber is stimulated to contract. Which sequence of events correctly describes the sliding filament mechanism?

Accepted Answer

Myosin heads bind to actin, pivot, detach, and repeat, causing actin filaments to slide past myosin and the sarcomere to shorten.

Question 9

Which of the following is a function of muscle tissue that is especially important for maintaining body temperature?

Accepted Answer

Generating heat

Question 10

A researcher measures the average muscle shortening during contraction and finds it to be approximately 30%. Which equation best represents the percentage of shortening if the original sarcomere length is $L_0$ and the contracted length is $L_c$?

Accepted Answer

$\frac{L_0 - L_c}{L_0} 	imes 100\%$

Question 11

Which protein blocks the active site on actin in a resting muscle, preventing myosin from binding?

Accepted Answer

Tropomyosin

Question 12

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

Accepted Answer

They transmit the action potential deep into the muscle fiber, triggering calcium release from the sarcoplasmic reticulum.

Question 13

Which of the following is true regarding the molecular composition of myofilaments?

Accepted Answer

Actin is a thin filament and myosin is a thick filament.

Question 14

A muscle cell is observed to have a large number of mitochondria and myoglobin. What is the most likely function of this cell?

Accepted Answer

Long-duration, aerobic activity

Question 15

Which connective tissue layer surrounds an entire muscle?

Accepted Answer

Epimysium

Question 16

Which of the following events occurs during the relaxation phase of muscle contraction?

Accepted Answer

Calcium ions are reclaimed by the sarcoplasmic reticulum, reducing cytoplasmic Ca$^{2+}$.

Question 17

Which of the following best describes the function of titin in the sarcomere?

Accepted Answer

It anchors thick filaments and provides elastic recoil to the muscle.

Question 18

Which of the following is NOT a function of muscle tissue?

Accepted Answer

Producing hormones

Question 19

Which equation correctly represents the conversion of ATP to ADP by myosin ATPase during muscle contraction?

Accepted Answer

$\mathrm{ATP} \rightarrow \mathrm{ADP} + \mathrm{P}_{i}$

Skeletal Muscle Structure and Function: Study Notes

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