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 is diagnosed with Duchenne muscular dystrophy (DMD). Which protein is defective, and what is the consequence for muscle fibers?

Accepted Answer

Dystrophin; muscle fibers become unstable and are easily damaged, leading to muscle degeneration.

Question 3

During the sliding filament model of contraction, what happens to the sarcomere as a muscle contracts?

Accepted Answer

The I bands shorten, Z discs move closer together, and the H zone disappears.

Question 4

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

Accepted Answer

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

Question 5

A muscle fiber is stimulated so rapidly that it does not have time to relax between stimuli, resulting in a smooth, sustained contraction. What is this phenomenon called?

Accepted Answer

Fused (complete) tetanus

Question 6

Which energy system provides the most ATP during prolonged, low-intensity exercise?

Accepted Answer

Aerobic pathway (glycolysis and aerobic respiration in mitochondria)

Question 7

Which of the following best explains why muscle fatigue occurs during intense exercise?

Accepted Answer

Ionic imbalances and increased inorganic phosphate disrupt excitation-contraction coupling and cross bridge cycling.

Question 8

Which type of muscle contraction occurs when you attempt to lift a heavy object but cannot move it, and what happens at the molecular level?

Accepted Answer

Isometric contraction; cross bridges generate force but actin filaments do not slide.

Question 9

Which of the following is a characteristic unique to cardiac muscle tissue?

Accepted Answer

It contracts at a steady rate due to its own pacemaker cells.

Question 10

A patient presents with drooping eyelids and muscle weakness. Laboratory tests reveal antibodies against acetylcholine receptors. What is the most likely diagnosis?

Accepted Answer

Myasthenia gravis

Question 11

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

Accepted Answer

ATP binds to myosin, causing cross bridge detachment from actin.

Question 12

Which muscle fiber type is most resistant to fatigue and best suited for maintaining posture?

Accepted Answer

Slow oxidative fibers

Question 13

What is the primary function of the connective tissue sheath known as the perimysium?

Accepted Answer

It surrounds fascicles, which are groups of muscle fibers.

Question 14

Which of the following is true regarding the length-tension relationship in skeletal muscle?

Accepted Answer

Maximum tension is generated when thick and thin filaments overlap optimally.

Question 15

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

Accepted Answer

Latch-bridge mechanism allows myosin to remain attached to actin for extended periods.

Question 16

Which of the following is a real-life example of an eccentric contraction?

Accepted Answer

Slowly lowering a heavy box to the ground

Question 17

Which of the following best describes the function of gap junctions in unitary smooth muscle?

Accepted Answer

They allow depolarization to spread from cell to cell, enabling coordinated contraction.

Question 18

A marathon runner is able to maintain muscle activity for hours. Which energy source is primarily used after 30 minutes of exercise?

Accepted Answer

Free fatty acids

Question 19

Which of the following is the correct formula for the direct phosphorylation of ADP by creatine phosphate?

Accepted Answer

$$\mathrm{Creatine\ phosphate + ADP \rightarrow Creatine + ATP}$$

Question 20

Which of the following is a distinguishing feature of multi-unit smooth muscle compared to unitary smooth muscle?

Accepted Answer

Multi-unit smooth muscle fibers are not electrically coupled and contract independently.

Muscles and Muscle Tissue: Structure, Function, and Physiology

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