Question 1

Which of the following best describes the role of the sodium-potassium ATPase pump in skeletal muscle fibers?

Accepted Answer

It actively transports three sodium ions out of the cell and two potassium ions in, maintaining the resting membrane potential. 
$$3	ext{Na}^+_{	ext{in}} ightarrow 3	ext{Na}^+_{	ext{out}}$$ 
$$2	ext{K}^+_{	ext{out}} ightarrow 2	ext{K}^+_{	ext{in}}$$

Question 2

A patient presents with muscle weakness and a waddling gait. Genetic testing reveals a mutation in the dystrophin gene. Which of the following best explains the pathophysiology of this condition?

Accepted Answer

Defective dystrophin disrupts the anchoring of the sarcolemma to the endomysium, causing muscle fiber death and replacement with connective tissue.

Question 3

During the contraction of a sarcomere, which of the following changes occur?

Accepted Answer

The I band and H zone narrow, while the A band remains unchanged.

Question 4

Which of the following is the correct sequence of events during the crossbridge cycle in skeletal muscle contraction?

Accepted Answer

Myosin binds ATP, detaches from actin, hydrolyzes ATP, binds actin, power stroke occurs.

Question 5

Which of the following best explains why rigor mortis occurs after death?

Accepted Answer

ATP is no longer available to pump calcium ions into the sarcoplasmic reticulum, so calcium remains in the cytosol and myosin heads cannot detach from actin.

Question 6

A muscle fiber is stimulated 90 times per second, resulting in a sustained contraction with maximal tension. Which term best describes this phenomenon?

Accepted Answer

Fused (complete) tetanus

Question 7

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

Accepted Answer

Presence of intercalated discs with gap junctions and desmosomes

Question 8

Which of the following best describes the role of creatine phosphate in muscle contraction?

Accepted Answer

It serves as an immediate source of phosphate to regenerate ATP from ADP during short bursts of activity. 
$$	ext{ADP} + 	ext{CP} \xrightarrow{	ext{CK}} 	ext{ATP} + 	ext{Creatine}$$

Question 9

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

Accepted Answer

Depletion of key metabolites, decreased oxygen availability, and accumulation of ADP and phosphate ions interfere with contraction.

Question 10

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

Accepted Answer

Maximum tension is produced when the sarcomere is at its optimal length, allowing for maximal crossbridge formation.

Question 11

Which of the following best describes the difference between single-unit and multi-unit smooth muscle?

Accepted Answer

Single-unit smooth muscle cells are connected by gap junctions and contract together, while multi-unit smooth muscle cells contract independently.

Question 12

Which of the following is a characteristic of slow oxidative (Type I) muscle fibers?

Accepted Answer

They contract slowly, have abundant mitochondria, and are resistant to fatigue.

Question 13

Which of the following events occurs during the excitation-contraction coupling phase of skeletal muscle contraction?

Accepted Answer

Calcium ions are released from the sarcoplasmic reticulum into the cytosol, triggering contraction.

Question 14

Which of the following best explains why botulinum toxin can be used therapeutically to treat muscle spasms?

Accepted Answer

It blocks the release of acetylcholine from motor neurons, preventing muscle contraction.

Question 15

Which of the following is a direct result of acetylcholinesterase activity at the neuromuscular junction?

Accepted Answer

Acetylcholine is degraded, ligand-gated cation channels close, and the muscle fiber relaxes.

Question 16

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

Accepted Answer

It binds oxygen, providing a reserve for oxidative catabolism during sustained activity.

Question 17

A person is performing a biceps curl and holds the weight stationary at a 90-degree angle. Which type of muscle contraction is occurring in the biceps brachii?

Accepted Answer

Isometric contraction

Question 18

Which of the following is a likely cause of delayed-onset muscle soreness (DOMS) after unaccustomed exercise?

Accepted Answer

Minor structural damage to myofilaments, especially from eccentric contractions

Question 19

Which of the following best describes the function of elastic filaments (titin) in the sarcomere?

Accepted Answer

They provide elasticity, resist excessive stretching, and help the muscle return to its original length.

Muscle Tissue and Physiology: Structure, Function, and Mechanisms

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