This compilation of Organization of Skeletal Muscle MCQs With Answer is designed for B. Pharm students to strengthen understanding of skeletal muscle structure and function. It covers muscle fiber organization, sarcomere anatomy, myofibrils, T-tubules and sarcoplasmic reticulum, excitation–contraction coupling, sliding filament mechanism, neuromuscular junction, muscle histology, fiber types, and clinical correlations. Each multiple-choice question targets core concepts, pharmacological relevance, and exam-oriented facts to build recall and application skills. Use these questions to review microanatomy, physiology, and drug interactions affecting muscle. Clear answers are provided to help self-assess and guide further study. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which protein anchors thin filaments to the Z-line and helps maintain sarcomere alignment?
- Myosin
- Titin
- Actinin
- Nebulin
Correct Answer: Actinin
Q2. The basic contractile unit of skeletal muscle, defined between two Z-lines, is called the:
- Myofibril
- Sarcomere
- Motor unit
- Sarcolemma
Correct Answer: Sarcomere
Q3. Which band of the sarcomere contains only thin (actin) filaments and appears lighter under microscopy?
- A-band
- I-band
- H-zone
- M-line
Correct Answer: I-band
Q4. Which protein provides passive elasticity and runs from Z-line to M-line within the sarcomere?
- Titin
- Desmin
- Troponin
- Alpha-actinin
Correct Answer: Titin
Q5. During excitation–contraction coupling, which structure relays the action potential deep into the muscle fiber?
- Sarcoplasmic reticulum
- Transverse (T) tubules
- Golgi tendon organ
- End plate
Correct Answer: Transverse (T) tubules
Q6. Release of calcium from the sarcoplasmic reticulum is primarily mediated by which receptor-channel complex?
- Acetylcholine receptor
- Ryanodine receptor
- Voltage-gated sodium channel
- SERCA pump
Correct Answer: Ryanodine receptor
Q7. Which regulatory protein binds calcium and causes tropomyosin displacement to expose myosin-binding sites on actin?
- Troponin C
- Tropomodulin
- Calmodulin
- Myosin light chain kinase
Correct Answer: Troponin C
Q8. The enzyme that hydrolyzes acetylcholine in the neuromuscular junction is:
- Acetylcholinesterase
- Choline acetyltransferase
- Monoamine oxidase
- Butyrylcholinesterase
Correct Answer: Acetylcholinesterase
Q9. A motor unit consists of a single motor neuron and:
- One sarcomere
- All muscle fibers in a muscle
- All muscle fibers it innervates
- One muscle fascicle
Correct Answer: All muscle fibers it innervates
Q10. Which muscle fiber type is most oxidative, fatigue-resistant, and rich in mitochondria and myoglobin?
- Type I
- Type IIa
- Type IIb (IIx)
- Type IIc
Correct Answer: Type I
Q11. Nebulin is thought to regulate which aspect of thin filaments?
- Length of thin filaments
- ATPase activity of myosin
- Calcium release from SR
- Attachment of myosin to titin
Correct Answer: Length of thin filaments
Q12. The H-zone of the sarcomere corresponds to the region containing:
- Only thin filaments
- Only thick filaments
- Overlap of thick and thin filaments
- Z-discs
Correct Answer: Only thick filaments
Q13. Which pump is responsible for resequestering calcium into the sarcoplasmic reticulum during muscle relaxation?
- Na+/K+ ATPase
- SERCA (SR Ca2+-ATPase)
- CIC-1 chloride channel
- NCX Na+/Ca2+ exchanger
Correct Answer: SERCA (SR Ca2+-ATPase)
Q14. Botulinum toxin produces muscle weakness by acting at the neuromuscular junction to:
- Block acetylcholine receptors
- Inhibit acetylcholine release from presynaptic terminals
- Prevent acetylcholine breakdown
- Activate ryanodine receptors
Correct Answer: Inhibit acetylcholine release from presynaptic terminals
Q15. The sliding filament theory primarily involves which interaction during contraction?
- Actin filaments sliding over myosin filaments via cross-bridge cycling
- Microtubules sliding past intermediate filaments
- Thick filaments shortening and pulling Z-lines inward
- Calcium filaments contracting within the sarcoplasm
Correct Answer: Actin filaments sliding over myosin filaments via cross-bridge cycling
Q16. Duchenne muscular dystrophy is caused by mutation in the gene encoding:
- Titin
- Dystrophin
- Myosin heavy chain
- Collagen type IV
Correct Answer: Dystrophin
Q17. Which histochemical staining method is classically used to differentiate muscle fiber types by ATPase activity?
- Hematoxylin and eosin (H&E)
- NADH-tetrazolium reductase
- ATPase staining at different pH levels
- Periodic acid–Schiff (PAS)
Correct Answer: ATPase staining at different pH levels
Q18. Malignant hyperthermia is most directly linked to abnormal function of which protein in skeletal muscle?
- Acetylcholinesterase
- Ryanodine receptor (RYR1)
- Troponin T
- SERCA1 pump
Correct Answer: Ryanodine receptor (RYR1)
Q19. Which event immediately follows cross-bridge formation between actin and myosin during the contraction cycle?
- Release of ADP and Pi and the power stroke
- ATP binding to myosin head and detachment
- Calcium binding to troponin I
- Phosphorylation of myosin light chain
Correct Answer: Release of ADP and Pi and the power stroke
Q20. In skeletal muscle, the primary role of satellite cells is to:
- Transmit action potentials
- Assist in muscle repair and regeneration
- Store calcium for contraction
- Provide ATP via glycolysis
Correct Answer: Assist in muscle repair and regeneration
Q21. Which statement best describes an isometric contraction?
- Muscle shortens while tension remains constant
- Muscle length remains constant while tension increases
- Muscle shortens against a constant load and moves it
- Muscle lengthens under tension
Correct Answer: Muscle length remains constant while tension increases
Q22. The end-plate potential at the motor end plate is generated primarily by opening of which ion channel?
- Voltage-gated calcium channels
- Ligand-gated nicotinic acetylcholine receptor channels (Na+/K+ permeable)
- Voltage-gated potassium channels
- Chloride channels
Correct Answer: Ligand-gated nicotinic acetylcholine receptor channels (Na+/K+ permeable)
Q23. Which pharmacologic agent produces a depolarizing neuromuscular block by persistent activation of nicotinic receptors?
- Curare (d-tubocurarine)
- Succinylcholine
- Neostigmine
- Pancuronium
Correct Answer: Succinylcholine
Q24. The length–tension relationship indicates that maximal active tension is produced when:
- Sarcomere length is extremely short and overlapped
- Sarcomere length is at an optimal overlap of actin and myosin
- Sarcomeres are fully extended with no overlap
- Muscle is fatigued
Correct Answer: Sarcomere length is at an optimal overlap of actin and myosin
Q25. Which sensory receptor located within muscle detects changes in muscle length and mediates stretch reflexes?
- Golgi tendon organ
- Muscle spindle (intrafusal fibers)
- Pacinian corpuscle
- Free nerve ending
Correct Answer: Muscle spindle (intrafusal fibers)
Q26. During sustained maximal stimulation, the fused tetanus occurs because:
- Action potentials are too infrequent to summate
- Calcium is cleared completely between twitches
- Intracellular calcium remains elevated preventing relaxation
- ATP is depleted and cross-bridges cannot cycle
Correct Answer: Intracellular calcium remains elevated preventing relaxation
Q27. Which molecule forms the thick filament and has ATPase activity essential for contraction?
- Actin
- Myosin II heavy chain
- Titin
- Alpha-actinin
Correct Answer: Myosin II heavy chain
Q28. The primary metabolic pathway supporting short bursts of intense skeletal muscle activity (seconds) is:
- Oxidative phosphorylation
- Glycolysis (anaerobic) and phosphocreatine system
- Ketogenesis
- Fatty acid beta-oxidation
Correct Answer: Glycolysis (anaerobic) and phosphocreatine system
Q29. Which structural protein links adjacent myofibrils at the Z-line and contributes to muscle fiber integrity?
- Desmin
- Troponin I
- Myomesin
- Nebulin
Correct Answer: Desmin
Q30. A drug that inhibits acetylcholinesterase would be expected to cause which effect at the neuromuscular junction?
- Decreased end-plate potential due to blocked ACh release
- Prolonged end-plate potential and enhanced muscle contraction
- Permanent depolarization and paralysis identical to succinylcholine
- Increased breakdown of choline
Correct Answer: Prolonged end-plate potential and enhanced muscle contraction
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