BIOD 151
Module 5 – Muscular System
Final Exam Review
2025
1. A 28-year-old woman with fluctuating muscle weakness notices worse symptoms at day’s en
Repetitive nerve stimulation shows a decremental compound muscle action potential. Which
mechanism underlies her condition?
a. Autoantibody blockade of acetylcholine receptors
b. Excessive acetylcholinesterase activity
c. Presynaptic depletion of acetylcholine vesicles
d. Mutation in voltage-gated sodium channels
ANS: a. Autoantibody blockade of acetylcholine receptors
Rationale: In myasthenia gravis, autoantibodies target postsynaptic nicotinic ACh receptor
reducing end-plate potentials and causing fatigable weakness.
2. A 7-year-old boy presents with Gowers’ sign and elevated creatine kinase. Genetic testing
confirms Duchenne muscular dystrophy. Which protein is deficient?
a. Dystrophin
b. Myosin heavy chain
c. Titin
d. Laminin
ANS: a. Dystrophin
Rationale: Duchenne muscular dystrophy arises from dystrophin absence, destabilizing the
sarcolemma and leading to muscle fiber necrosis.
3. A marathon runner collapses post-race with dark-colored urine and elevated serum CK and
myoglobin. Acute kidney injury follows. What is the primary nephrotoxic mechanism?
a. Myoglobin precipitation in renal tubules
b. Immune-complex deposition in glomeruli
c. Tubular toxicity from lactate accumulation
d. Hemodynamic vasoconstriction from catecholamines
ANS: a. Myoglobin precipitation in renal tubules
, Rationale: Excessive myoglobin released in rhabdomyolysis precipitates in distal tubules,
obstructing flow and inducing oxidative injury.
4. A 55-year-old weightlifter reports muscle “burn” during high-intensity sets. Intracellular
inorganic phosphate accumulates. How does this metabolite impair force generation?
a. Inhibits Ca²⁺ release from the sarcoplasmic reticulum
b. Competes with Ca²⁺ for troponin binding
c. Reduces cross-bridge detachment rate
d. Decreases myosin head conformational change
ANS: d. Decreases myosin head conformational change
Rationale: Elevated inorganic phosphate slows the power stroke of myosin heads, reducin
force output and contributing to fatigue.
5. A patient with hypocalcemia develops muscle tetany. Which electrophysiologic change at the
neuromuscular junction explains increased excitability?
a. Lowered threshold for action potential initiation
b. Prolonged repolarization of the motor end plate
c. Blockade of voltage-gated sodium channels
d. Decreased acetylcholine release
ANS: a. Lowered threshold for action potential initiation
Rationale: Hypocalcemia reduces extracellular Ca²⁺, destabilizing membrane potentials an
lowering the threshold for Na⁺ channel opening, eliciting tetany.
6. An elderly patient performing an eccentric squat experiences more muscle microtears than
during concentric contraction. Which principle explains higher force during eccentric activity?
a. Greater cross-bridge recruitment at longer sarcomere lengths
b. Increased ATP hydrolysis per cross-bridge cycle
c. Higher myosin ATPase activity in eccentric mode
d. Enhanced Ca²⁺ sensitivity of troponin C
ANS: a. Greater cross-bridge recruitment at longer sarcomere lengths
Rationale: Eccentric contractions produce more force due to passive tension in titin and
stronger cross-bridge binding at stretched sarcomere lengths.
7. A patient with a pheochromocytoma has elevated catecholamines and develops tremors.
Which muscle type mediates fine tremor via α-adrenergic receptors?
a. Multiunit smooth muscle
b. Single-unit smooth muscle
c. Cardiac muscle
d. Skeletal muscle
, ANS: a. Multiunit smooth muscle
Rationale: Multiunit smooth muscle (e.g., in piloerector muscles) responds to neural and
hormonal input via α-adrenergic receptors, causing fine tremor-like contractions.
8. During a 100-meter sprint, which ATP generation pathway predominates in fast-twitch muscl
fibers?
a. Oxidative phosphorylation
b. Phosphocreatine system
c. Anaerobic glycolysis
d. β-oxidation of fatty acids
ANS: b. Phosphocreatine system
Rationale: The phosphagen system rapidly donates phosphate from creatine phosphate to
ADP, providing immediate ATP for short, intense bursts.
9. Sarcopenia in aging preferentially affects which skeletal muscle fiber type?
a. Type I oxidative
b. Type IIa fast oxidative
c. Type IIb fast glycolytic
d. Smooth muscle fibers
ANS: c. Type IIb fast glycolytic
Rationale: Aging leads to denervation and atrophy of type II glycolytic fibers, reducing peak
force and power output.
10. A patient under general anesthesia with succinylcholine develops malignant hyperthermia
and hyperkalemia. Which receptor mutation predisposes to this crisis?
a. Dihydropyridine receptor (DHPR)
b. Ryanodine receptor (RyR1)
c. Nicotinic ACh receptor
d. SERCA pump
ANS: b. Ryanodine receptor (RyR1)
Rationale: RyR1 mutations cause uncontrolled Ca²⁺ release from the sarcoplasmic
reticulum when exposed to certain anesthetics, triggering hypermetabolism and hyperthermia.
11. After intense exercise, heavy breathing persists. Which process contributes most to excess
post-exercise oxygen consumption (EPOC)?
a. Restoration of phosphocreatine stores
b. Replenishment of hepatic glycogen
c. Clearance of accumulated CO₂
, d. Oxidation of ketone bodies
ANS: a. Restoration of phosphocreatine stores
Rationale: Re‐synthesis of creatine phosphate requires ATP and O₂, accounting for a
significant portion of EPOC.
12. Following a muscle strain, satellite cells become activated. What is their primary role in
muscle repair?
a. Fusing to existing fibers to provide new nuclei
b. Replacing damaged sarcoplasmic reticulum
c. Transforming into fibroblasts for scar tissue
d. Inhibiting inflammation
ANS: a. Fusing to existing fibers to provide new nuclei
Rationale: Satellite cells proliferate and fuse with injured muscle fibers, contributing
myonuclei that support regeneration and hypertrophy.
---
Fill-in-the-Blank (6 Questions)
13. The smallest contractile unit of skeletal muscle, delineated by Z discs, is called the
__________.
ANS: sarcomere
Rationale: Sarcomeres contain overlapping actin and myosin filaments and are the
functional units of muscle contraction.
14. Calcium ions bind to __________ on the thin filament to initiate conformational changes
exposing myosin-binding sites.
ANS: troponin C
Rationale: Troponin C’s Ca²⁺ binding shifts tropomyosin off actin’s active sites, enabling
cross-bridge cycling.
15. The rapid depolarization of the T-tubule membrane that triggers Ca²⁺ release from the
sarcoplasmic reticulum is conducted by the __________ receptor.
ANS: dihydropyridine
Rationale: DHPR senses voltage changes and mechanically couples to ryanodine recepto
to release stored Ca²⁺.
Module 5 – Muscular System
Final Exam Review
2025
1. A 28-year-old woman with fluctuating muscle weakness notices worse symptoms at day’s en
Repetitive nerve stimulation shows a decremental compound muscle action potential. Which
mechanism underlies her condition?
a. Autoantibody blockade of acetylcholine receptors
b. Excessive acetylcholinesterase activity
c. Presynaptic depletion of acetylcholine vesicles
d. Mutation in voltage-gated sodium channels
ANS: a. Autoantibody blockade of acetylcholine receptors
Rationale: In myasthenia gravis, autoantibodies target postsynaptic nicotinic ACh receptor
reducing end-plate potentials and causing fatigable weakness.
2. A 7-year-old boy presents with Gowers’ sign and elevated creatine kinase. Genetic testing
confirms Duchenne muscular dystrophy. Which protein is deficient?
a. Dystrophin
b. Myosin heavy chain
c. Titin
d. Laminin
ANS: a. Dystrophin
Rationale: Duchenne muscular dystrophy arises from dystrophin absence, destabilizing the
sarcolemma and leading to muscle fiber necrosis.
3. A marathon runner collapses post-race with dark-colored urine and elevated serum CK and
myoglobin. Acute kidney injury follows. What is the primary nephrotoxic mechanism?
a. Myoglobin precipitation in renal tubules
b. Immune-complex deposition in glomeruli
c. Tubular toxicity from lactate accumulation
d. Hemodynamic vasoconstriction from catecholamines
ANS: a. Myoglobin precipitation in renal tubules
, Rationale: Excessive myoglobin released in rhabdomyolysis precipitates in distal tubules,
obstructing flow and inducing oxidative injury.
4. A 55-year-old weightlifter reports muscle “burn” during high-intensity sets. Intracellular
inorganic phosphate accumulates. How does this metabolite impair force generation?
a. Inhibits Ca²⁺ release from the sarcoplasmic reticulum
b. Competes with Ca²⁺ for troponin binding
c. Reduces cross-bridge detachment rate
d. Decreases myosin head conformational change
ANS: d. Decreases myosin head conformational change
Rationale: Elevated inorganic phosphate slows the power stroke of myosin heads, reducin
force output and contributing to fatigue.
5. A patient with hypocalcemia develops muscle tetany. Which electrophysiologic change at the
neuromuscular junction explains increased excitability?
a. Lowered threshold for action potential initiation
b. Prolonged repolarization of the motor end plate
c. Blockade of voltage-gated sodium channels
d. Decreased acetylcholine release
ANS: a. Lowered threshold for action potential initiation
Rationale: Hypocalcemia reduces extracellular Ca²⁺, destabilizing membrane potentials an
lowering the threshold for Na⁺ channel opening, eliciting tetany.
6. An elderly patient performing an eccentric squat experiences more muscle microtears than
during concentric contraction. Which principle explains higher force during eccentric activity?
a. Greater cross-bridge recruitment at longer sarcomere lengths
b. Increased ATP hydrolysis per cross-bridge cycle
c. Higher myosin ATPase activity in eccentric mode
d. Enhanced Ca²⁺ sensitivity of troponin C
ANS: a. Greater cross-bridge recruitment at longer sarcomere lengths
Rationale: Eccentric contractions produce more force due to passive tension in titin and
stronger cross-bridge binding at stretched sarcomere lengths.
7. A patient with a pheochromocytoma has elevated catecholamines and develops tremors.
Which muscle type mediates fine tremor via α-adrenergic receptors?
a. Multiunit smooth muscle
b. Single-unit smooth muscle
c. Cardiac muscle
d. Skeletal muscle
, ANS: a. Multiunit smooth muscle
Rationale: Multiunit smooth muscle (e.g., in piloerector muscles) responds to neural and
hormonal input via α-adrenergic receptors, causing fine tremor-like contractions.
8. During a 100-meter sprint, which ATP generation pathway predominates in fast-twitch muscl
fibers?
a. Oxidative phosphorylation
b. Phosphocreatine system
c. Anaerobic glycolysis
d. β-oxidation of fatty acids
ANS: b. Phosphocreatine system
Rationale: The phosphagen system rapidly donates phosphate from creatine phosphate to
ADP, providing immediate ATP for short, intense bursts.
9. Sarcopenia in aging preferentially affects which skeletal muscle fiber type?
a. Type I oxidative
b. Type IIa fast oxidative
c. Type IIb fast glycolytic
d. Smooth muscle fibers
ANS: c. Type IIb fast glycolytic
Rationale: Aging leads to denervation and atrophy of type II glycolytic fibers, reducing peak
force and power output.
10. A patient under general anesthesia with succinylcholine develops malignant hyperthermia
and hyperkalemia. Which receptor mutation predisposes to this crisis?
a. Dihydropyridine receptor (DHPR)
b. Ryanodine receptor (RyR1)
c. Nicotinic ACh receptor
d. SERCA pump
ANS: b. Ryanodine receptor (RyR1)
Rationale: RyR1 mutations cause uncontrolled Ca²⁺ release from the sarcoplasmic
reticulum when exposed to certain anesthetics, triggering hypermetabolism and hyperthermia.
11. After intense exercise, heavy breathing persists. Which process contributes most to excess
post-exercise oxygen consumption (EPOC)?
a. Restoration of phosphocreatine stores
b. Replenishment of hepatic glycogen
c. Clearance of accumulated CO₂
, d. Oxidation of ketone bodies
ANS: a. Restoration of phosphocreatine stores
Rationale: Re‐synthesis of creatine phosphate requires ATP and O₂, accounting for a
significant portion of EPOC.
12. Following a muscle strain, satellite cells become activated. What is their primary role in
muscle repair?
a. Fusing to existing fibers to provide new nuclei
b. Replacing damaged sarcoplasmic reticulum
c. Transforming into fibroblasts for scar tissue
d. Inhibiting inflammation
ANS: a. Fusing to existing fibers to provide new nuclei
Rationale: Satellite cells proliferate and fuse with injured muscle fibers, contributing
myonuclei that support regeneration and hypertrophy.
---
Fill-in-the-Blank (6 Questions)
13. The smallest contractile unit of skeletal muscle, delineated by Z discs, is called the
__________.
ANS: sarcomere
Rationale: Sarcomeres contain overlapping actin and myosin filaments and are the
functional units of muscle contraction.
14. Calcium ions bind to __________ on the thin filament to initiate conformational changes
exposing myosin-binding sites.
ANS: troponin C
Rationale: Troponin C’s Ca²⁺ binding shifts tropomyosin off actin’s active sites, enabling
cross-bridge cycling.
15. The rapid depolarization of the T-tubule membrane that triggers Ca²⁺ release from the
sarcoplasmic reticulum is conducted by the __________ receptor.
ANS: dihydropyridine
Rationale: DHPR senses voltage changes and mechanically couples to ryanodine recepto
to release stored Ca²⁺.
