Free Muscle Contraction MCQs with Answers

• A. myofilament
• B. sarcomere
• C. sarcolemma
• D. sarcoplasmic reticulum

Explanation: A sarcomere is the region between two Z lines, containing overlapping thick and thin filaments, and the whole muscle shortens because…

• A. I band
• B. H zone
• C. Sarcomere
• D. A band

Explanation: The A band is the full length of the thick myosin filaments, and since the filaments themselves do not shorten, the A band stays the same…

• A. actin filaments slide inwards over the myosin filaments
• B. both actin and myosin filaments themselves shorten
• C. the sarcomere is stretched by the load
• D. the Z lines dissolve and reform further apart

Explanation: Myosin heads bind actin, swivel, and drag the thin filaments towards the centre of the sarcomere, then detach and repeat, so the filaments…

• A. the myosin heads
• B. tropomyosin directly
• C. troponin, which moves tropomyosin off the binding sites on actin
• D. ATP, activating it

Explanation: In a relaxed fibre tropomyosin lies across the myosin binding sites of actin.

• A. calcium ions disappear from the sarcoplasm
• B. ATP is no longer available to detach the myosin heads from actin
• C. the muscle proteins are denatured by the fall in body temperature
• D. acetylcholine continues to be released at the neuromuscular junction

Explanation: ATP is needed not to form a cross bridge but to break one, so when respiration stops and ATP runs out the myosin heads stay locked on…

• A. noradrenaline
• B. dopamine
• C. acetylcholine
• D. GABA

Explanation: Acetylcholine diffuses across the synaptic cleft and depolarises the sarcolemma, and the resulting action potential spreads down the T…

• A. Actin and myosin
• B. Tropomyosin only
• C. Troponin only
• D. Collagen

Explanation: Muscle contraction involves sliding of actin (thin) filaments past myosin (thick) filaments.

• A. Myofibril
• B. Sarcomere
• C. Muscle fiber
• D. Tendon

Explanation: The sarcomere (between two Z-lines) is the basic functional unit of muscle contraction.

• A. Actin
• B. Myosin
• C. Troponin
• D. Tropomyosin

Explanation: Ca2+ binds to troponin, causing tropomyosin to move and expose myosin-binding sites on actin.

• A. Only cross-bridge formation
• B. Only cross-bridge detachment
• C. Both formation and detachment
• D. Neither

Explanation: ATP is required for myosin head cocking (after power stroke) and detachment from actin.

• A. Excess ATP
• B. Lack of ATP
• C. Excess calcium
• D. Lack of calcium

Explanation: Without ATP, myosin heads cannot detach from actin, causing persistent muscle contraction (rigor mortis).

• A. Only actin
• B. Only myosin
• C. Both actin and myosin
• D. Neither

Explanation: The A-band (dark) contains the entire length of myosin filaments and overlapping actin filaments.

• A. Actin blocks the myosin binding site
• B. Tropomyosin blocks the myosin binding site
• C. Troponin blocks the myosin binding site
• D. Tropomyosin blocks the troponin binding site

Explanation: In a relaxed fibre the long tropomyosin strand lies across the myosin binding sites on actin, so no cross bridge can form.

• A. Actin and myosin form a cross-bridge
• B. Calcium is pumped back into the sarcoplasmic reticulum
• C. Calcium is released from the sarcoplasmic reticulum
• D. ATP is hydrolyzed by troponin

Explanation: The action potential travels down the T tubules and triggers the sarcoplasmic reticulum to release calcium, which then binds troponin and…

• A. Acidic acid
• B. Butyric acid
• C. Citric acid
• D. Lactic acid

Explanation: During intense exercise, oxygen delivery may not meet demand, so muscle cells rely more on anaerobic glycolysis and convert pyruvate to…

• A. Hypocalcemia
• B. Hypercalcemia
• C. Clostridum tetani.
• D. Low O2 level

Explanation: Tetany is caused by hypocalcemia, or a reduced concentration of calcium ions in the blood, which increases nerve and muscle excitability…

• A. The major event in it is accumulation of lactic acid.
• B. Lactic acid accumulation turns pH in acidic range leading to muscle ache.
• C. Ionic imbalance may also cause it.
• D. All of these

Explanation: Muscle fatigue may involve lactate and hydrogen ion accumulation, changes in pH, and ionic disturbances that interfere with excitation and…

• A. Accunulation of rigid proteins molecules in sarcoplam.
• B. Unavailability of ATP, which is necessary to break the link between actin and myosin.
• C. Decrease in body temperature after death.
• D. Death of tissue due to unavailability of O2.

Explanation: After death, ATP production stops, so myosin heads cannot detach from actin because ATP is required for their release.

• A. Z- lines get closer
• B. A band becomes short
• C. 1 band elongates
• D. There is no change in sarcomere

Explanation: During contraction, actin slides over myosin without either filament changing length, bringing the two Z-lines closer together.

• A. 9
• B. 5
• C. 6
• D. 7

Explanation: In a cross-section of the sarcomere, each thick filament lies at the centre of a hexagonal arrangement and is surrounded by six thin actin…