Mechanism of Muscle Contraction — NEET Biology MCQs with Solutions
Free NEET Biology Mechanism of Muscle Contraction MCQs with step-by-step solutions (38 questions). Part of Locomotion and Movement. Practise online on Prepizo — no login needed.
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Questions with solutions
Q1 — Mechanism of Muscle Contraction · easy · theory
The ion whose release from the sarcoplasmic reticulum triggers muscle contraction is:
A. Calcium (Ca²⁺) ✓ Correct
B. Sodium (Na⁺)
C. Potassium (K⁺)
D. Chloride (Cl⁻)
Solution: A nerve impulse causes Ca²⁺ release, which initiates the contraction cycle by exposing actin binding sites.
Q2 — Mechanism of Muscle Contraction · easy · theory
The neurotransmitter released at the neuromuscular junction to stimulate a muscle fibre is:
A. Insulin
B. Acetylcholine ✓ Correct
C. Adrenaline
D. Dopamine
Solution: Acetylcholine released at the motor end-plate depolarises the sarcolemma, initiating contraction.
Q3 — Mechanism of Muscle Contraction · medium · theory
Ca²⁺ initiates contraction by binding to ______, which moves ______ to expose the myosin-binding sites on actin:
A. Tropomyosin; troponin
B. Actin; myoglobin
C. Troponin; tropomyosin ✓ Correct
D. Myosin; actin
Solution: Ca²⁺ binds troponin, shifting tropomyosin away from actin's binding sites so cross-bridges can form.
Q4 — Mechanism of Muscle Contraction · medium · theory
The energy for the sliding of filaments (breaking of the actin-myosin cross-bridge) comes from:
A. Hydrolysis of ATP ✓ Correct
B. Lactic acid
C. Ca²⁺ binding alone
D. Oxygen alone
Solution: ATP binds the myosin head to release it from actin; its hydrolysis re-cocks the head for the next stroke.
Q5 — Mechanism of Muscle Contraction · hard · theory
The reddish muscle fibres that resist fatigue contain abundant ______ and rely on ______ respiration:
A. Actin only; anaerobic
B. Glycogen only; anaerobic
C. Myoglobin/mitochondria; aerobic ✓ Correct
D. Calcium; fermentation
Solution: Red (type I) fibres have plentiful myoglobin and mitochondria, favouring aerobic respiration and endurance.
Q6 — Mechanism of Muscle Contraction · hard · theory
The rigor mortis (stiffening of muscles after death) occurs because:
A. Muscles keep contracting with energy
B. ATP is no longer available to detach the myosin heads from actin ✓ Correct
C. Calcium is completely removed
D. Too much ATP is present
Solution: Without ATP, cross-bridges cannot detach, so actin and myosin remain locked — causing rigor mortis.
Q7 — Mechanism of Muscle Contraction · easy · numerical
According to the sliding filament theory, muscle contraction occurs when:
A. Thin filaments slide over thick filaments, shortening the sarcomere ✓ Correct
B. Only the thick filaments contract while the thin ones lengthen
C. Both thin and thick filaments shorten in length
D. The Z lines dissolve and the myofibrils fuse together
Solution: In the sliding filament theory the filaments themselves do not shorten; the thin filaments slide inward over the stationary thick filaments, pulling the Z lines closer and shortening the sarcomere.
Q8 — Mechanism of Muscle Contraction · easy · numerical
The signal that spreads from the neuromuscular junction into the muscle fibre and triggers Ca²⁺ release is a:
A. Wave of hyperpolarisation
B. Wave of depolarisation (action potential) ✓ Correct
C. Direct flow of ATP molecules
D. Rise in blood oxygen level
Solution: Acetylcholine generates an action potential (depolarisation wave) that travels along the sarcolemma and T-tubules, causing the sarcoplasmic reticulum to release stored calcium ions.
Q9 — Mechanism of Muscle Contraction · easy · numerical
During muscle contraction, the cross bridges are formed between:
A. Two adjacent actin filaments
B. The myosin heads and the active sites on actin ✓ Correct
C. The Z line and the M line
D. Troponin and tropomyosin
Solution: The globular heads of myosin bind to exposed active sites on actin to form cross bridges; the subsequent bending of these heads (power stroke) pulls the actin filament inward.
Q10 — Mechanism of Muscle Contraction · easy · numerical
Which molecule directly supplies the energy needed for the myosin head to detach from actin and re-cock during contraction?
A. Lactic acid
B. Glucose
C. Creatine
D. ATP ✓ Correct
Solution: ATP binds the myosin head causing it to release actin, and its hydrolysis re-energises (re-cocks) the head for the next cycle. Glucose and creatine are ultimate fuel sources but do not act directly on myosin.
Q11 — Mechanism of Muscle Contraction · medium · numerical
Arrange the events of muscle contraction in the correct sequence: (i) Ca²⁺ binds troponin and shifts tropomyosin (ii) action potential reaches the sarcoplasmic reticulum (iii) myosin head binds actin and performs the power stroke (iv) Ca²⁺ is released into the sarcoplasm.
A. (ii) → (i) → (iv) → (iii)
B. (i) → (ii) → (iv) → (iii)
C. (iv) → (ii) → (i) → (iii)
D. (ii) → (iv) → (i) → (iii) ✓ Correct
Solution: The action potential reaches the sarcoplasmic reticulum, calcium is released, calcium binds troponin to move tropomyosin off the active sites, and then the myosin head binds actin and executes the power stroke.
Q12 — Mechanism of Muscle Contraction · medium · numerical
Assertion (A): In a relaxed muscle the myosin-binding sites on actin are masked. Reason (R): Tropomyosin, positioned along the actin filament, covers the active sites until calcium binds troponin. Choose the correct option.
A. A is false but R is true
B. Both A and R are true but R is not the correct explanation of A
C. A is true but R is false
D. Both A and R are true and R is the correct explanation of A ✓ Correct
Solution: At rest tropomyosin overlies the actin active sites, blocking cross-bridge formation. Calcium binding to troponin shifts tropomyosin to expose the sites, so R correctly explains the masking stated in A.
Q13 — Mechanism of Muscle Contraction · medium · numerical
The reddish-brown pigment in muscle that binds oxygen and acts as an oxygen store, abundant in fatigue-resistant fibres, is:
A. Myoglobin ✓ Correct
B. Cytochrome
C. Haemoglobin
D. Melanin
Solution: Myoglobin is the oxygen-binding pigment stored in muscle, plentiful in red (slow oxidative) fibres, allowing them to sustain aerobic respiration and resist fatigue. Haemoglobin performs oxygen transport in blood.
Q14 — Mechanism of Muscle Contraction · medium · numerical
Repeated, strenuous exercise can lead to muscle fatigue mainly because of the accumulation of:
A. Excess oxygen in the muscle fibres
B. Creatine phosphate around the myofibrils
C. Too much calcium in the sarcoplasmic reticulum
D. Lactic acid from anaerobic breakdown of glycogen ✓ Correct
Solution: When oxygen supply is insufficient, glycogen is broken down anaerobically to lactic acid, whose build-up causes muscle fatigue. Calcium and creatine phosphate do not accumulate to cause fatigue in this way.
Q15 — Mechanism of Muscle Contraction · medium · numerical
Which statement about the role of calcium in muscle relaxation is correct?
A. Ca²⁺ diffuses out of the fibre across the sarcolemma permanently
B. Ca²⁺ is pumped back into the sarcoplasmic reticulum, masking the actin sites again ✓ Correct
C. Ca²⁺ remains bound to troponin, keeping the actin sites exposed
D. Ca²⁺ is broken down by ATPase during relaxation
Solution: Relaxation follows when calcium is actively pumped back into the sarcoplasmic reticulum; troponin–tropomyosin then re-masks the active sites, cross bridges break, and the sarcomere returns to its resting length.
Q16 — Mechanism of Muscle Contraction · medium · numerical
During the shortening of a contracting sarcomere, which of the following statements is TRUE?
A. Both the A band and I band shorten equally
B. The I band and H zone shorten while the A band length stays constant ✓ Correct
C. The A band shortens while the I band remains constant
D. Only the H zone widens as the muscle contracts
Solution: As thin filaments slide inward, the I band (thin-only region) and the H zone (thick-only region) shrink, but the A band, equal to the fixed length of the thick filaments, is unchanged.
Q17 — Mechanism of Muscle Contraction · easy · theory
Huxley gave the ______ theory to explain muscular contraction.
A. Ratchet
B. Fluid mosaic
C. Lock and key
D. Sliding filament ✓ Correct
Solution: Huxley proposed the sliding filament theory, in which thin filaments slide over thick filaments.
Q18 — Mechanism of Muscle Contraction · easy · theory
Motor end plate is the junction between _____ of the muscle fibre.
A. Two nerve cells
B. Motor neuron and the sarcolemma ✓ Correct
C. Sarcolemma and sarcoplasm
D. Two muscle fibres
Solution: The motor end plate (neuromuscular junction) is where a motor neuron meets the sarcolemma of the muscle fibre.
Q19 — Mechanism of Muscle Contraction · medium · theory
In striped muscles, cross bridges rapidly dissociate when
A. Calcium binds to tropomyosin
B. Troponin-tropomyosin complex masks the active binding sites for myosin on the actin filaments
C. ATP attaches to the myosin head ✓ Correct
D. ADP and inorganic phosphate separates from myosin head
Solution: Binding of a new ATP molecule to the myosin head causes the cross bridge to detach from actin.
Q20 — Mechanism of Muscle Contraction · easy · theory
During muscle contraction,
A. Mechanical energy is changed into chemical energy
B. Chemical energy is changed into electrical energy
C. Chemical energy is changed into mechanical energy ✓ Correct
D. Chemical energy is changed into light energy
Solution: Muscle contraction converts the chemical energy of ATP into mechanical work (movement).
Q21 — Mechanism of Muscle Contraction · medium · theory
Electron microscopic studies of the sarcomeres have revealed that during muscle contraction
A. The diameter of the fibre increases
B. The length of A-band decreases
C. The width of I-band increases
D. The length of A-band remains constant ✓ Correct
Solution: During contraction the A-band stays constant in length while the I-band and H-zone shorten.
Q22 — Mechanism of Muscle Contraction · easy · theory
According to sliding filament theory of muscle contraction, the filament that moves to shorten a muscle fibre is
A. Actin ✓ Correct
B. Creatine phosphate
C. Collagen
D. Myosin
Solution: The thin actin filaments slide over the stationary myosin filaments, shortening the sarcomere.
Q23 — Mechanism of Muscle Contraction · easy · theory
During muscle contraction in a skeletal muscle fibre, Ca2+ combines with
A. Actin
B. Troponin ✓ Correct
C. Myosin
D. Tropomyosin
Solution: Calcium ions bind to troponin, shifting tropomyosin and exposing the myosin-binding sites on actin.
Q24 — Mechanism of Muscle Contraction · easy · theory
Muscle fatigue occurs due to the accumulation of
A. Creatine phosphate
B. Lactic acid ✓ Correct
C. Myosin ATPase
D. CO2
Solution: Anaerobic respiration during heavy exertion accumulates lactic acid, causing muscle fatigue.
Q25 — Mechanism of Muscle Contraction · hard · theory
During muscle contraction, what could be the correct sequence? A. Release of calcium ions into the sarcoplasm. B. Release of acetylcholine. C. Sliding of actin filaments over each other. D. Breakdown of ATP to form a cross bridge.
A. B, A, D, C ✓ Correct
B. B, A, C, D
C. A, B, D, C
D. A, D, B, C
Solution: Acetylcholine release -> Ca2+ release into sarcoplasm -> ATP breakdown for cross bridge -> sliding of actin filaments.
Q26 — Mechanism of Muscle Contraction · hard · theory
Find out the set of correct statements. A. Meromyosin is the monomeric protein of myosin. B. Each meromyosin has head as HMM and tail as LMM. C. Increase in Ca2+ level leads to binding of Ca with a subunit of tropomyosin on actin filament. D. ATP hydrolysis is done by myosin head to make cross bridge.
A. B, C, D
B. A, B, D ✓ Correct
C. A, D
D. A, B, C
Solution: A, B and D are correct; C is wrong because Ca2+ binds troponin (not tropomyosin).
Q27 — Mechanism of Muscle Contraction · medium · theory
Read the following statements about muscle tissue and choose the correct option. I. Excessive exercise results in anaerobic respiration and forms lactic acid. II. As per sliding filament theory, the filament that moves to shorten a muscle is actin. III. The muscles primarily involved in locomotion are striated muscles.
A. I and II only
B. I, II and III ✓ Correct
C. I and III only
D. II and III only
Solution: All three are correct: exercise causes lactic acid build-up, thin actin filaments slide inward, and striated skeletal muscles drive locomotion.
Q28 — Mechanism of Muscle Contraction · hard · theory
Choose the incorrect statement(s). A. A motor neuron along with the muscle fibre connected to it constitutes a motor-end plate. B. Muscle contraction is initiated by a signal sent by the CNS via a sensory neuron. C. Sliding filament theory states that contraction takes place by the sliding of the thick filaments over the thin filaments.
A. A, B, C ✓ Correct
B. A, C
C. B, C
D. A, B
Solution: All are wrong: that junction is the neuromuscular junction/motor unit, the signal travels via a motor neuron, and thin filaments slide over thick filaments.
Q29 — Mechanism of Muscle Contraction · hard · theory
Find out the correct statements. A. Meromyosin is the monomeric protein of actin. B. Each meromyosin has head as LMM and tail as HMM. C. Increase in Ca level leads to binding of Ca with a subunit of troponin on actin filament. D. ATP hydrolysis is done by actin head to make cross arm.
A. A, B
B. A, B, D
C. Only C ✓ Correct
D. B, C, D
Solution: Only C is correct; meromyosin is of myosin, its head is HMM/tail LMM, and ATP is hydrolysed by the myosin head.
Q30 — Mechanism of Muscle Contraction · medium · theory
Which of the statements about the mechanism of muscle contraction are correct? I. Acetylcholine is released when the neural signal reaches the motor end plate. II. Muscle contraction is initiated by a signal sent by CNS via a sensory neuron. III. During muscle contraction, isotropic band gets elongated. IV. Repeated activation of the muscles can lead to lactic acid accumulation.
A. I, II and III are correct
B. II and III are correct
C. I and IV are correct ✓ Correct
D. I and III are correct
Solution: I and IV are correct; the signal is via a motor neuron (II wrong) and the isotropic I band shortens during contraction (III wrong).