Q.1 Which protein directly binds calcium to initiate muscle contraction?
Myosin
Actin
Troponin C
Tropomyosin
Explanation - Troponin C binds calcium, causing a conformational change that moves tropomyosin away from actin’s binding site, allowing myosin interaction.
Correct answer is: Troponin C
Q.2 What is the functional unit of a muscle fiber?
Myofibril
Sarcomere
Myofilament
Motor unit
Explanation - The sarcomere, defined between two Z-lines, is the basic contractile unit of striated muscle.
Correct answer is: Sarcomere
Q.3 Which ion is essential for muscle contraction?
Sodium
Calcium
Potassium
Chloride
Explanation - Calcium ions trigger contraction by binding to troponin and enabling actin-myosin cross-bridge formation.
Correct answer is: Calcium
Q.4 During muscle contraction, which band shortens?
A band
I band
H zone
Z line
Explanation - The I band and H zone shorten during contraction, while the A band remains constant.
Correct answer is: I band
Q.5 Which neurotransmitter is released at the neuromuscular junction?
Dopamine
Acetylcholine
Norepinephrine
GABA
Explanation - Acetylcholine is the neurotransmitter that stimulates skeletal muscle contraction at the neuromuscular junction.
Correct answer is: Acetylcholine
Q.6 The energy for muscle contraction is directly provided by:
Glucose
ATP
Creatine phosphate
NADH
Explanation - ATP is directly hydrolyzed by myosin ATPase to provide energy for cross-bridge cycling.
Correct answer is: ATP
Q.7 Which structure stores calcium in skeletal muscle cells?
Mitochondria
Sarcolemma
Sarcoplasmic reticulum
Golgi apparatus
Explanation - The sarcoplasmic reticulum stores and releases calcium during excitation-contraction coupling.
Correct answer is: Sarcoplasmic reticulum
Q.8 What is the primary role of tropomyosin?
ATP hydrolysis
Blocking actin binding sites
Binding calcium
Storing oxygen
Explanation - Tropomyosin covers actin’s myosin-binding sites, preventing contraction until calcium binds to troponin.
Correct answer is: Blocking actin binding sites
Q.9 Which type of muscle is involuntary and striated?
Smooth muscle
Cardiac muscle
Skeletal muscle
Connective tissue
Explanation - Cardiac muscle is striated like skeletal muscle but involuntary like smooth muscle.
Correct answer is: Cardiac muscle
Q.10 What is the latent period in a muscle twitch?
Time of contraction
Time of relaxation
Time between stimulus and contraction onset
Time of fatigue
Explanation - The latent period is the brief delay between stimulus application and muscle contraction.
Correct answer is: Time between stimulus and contraction onset
Q.11 Which enzyme breaks down acetylcholine at the neuromuscular junction?
Monoamine oxidase
Cholinesterase
Acetylcholinesterase
Catechol-O-methyltransferase
Explanation - Acetylcholinesterase rapidly degrades acetylcholine to terminate muscle stimulation.
Correct answer is: Acetylcholinesterase
Q.12 What is a motor unit?
A single sarcomere
A neuron and all muscle fibers it innervates
One myofibril
A neuromuscular junction
Explanation - A motor unit is the functional entity controlling muscle contraction strength.
Correct answer is: A neuron and all muscle fibers it innervates
Q.13 Which type of skeletal muscle fiber is fatigue-resistant and suited for endurance?
Type I (slow-twitch)
Type IIa
Type IIb
Intermediate fibers
Explanation - Type I fibers are rich in mitochondria, myoglobin, and capillaries, enabling endurance.
Correct answer is: Type I (slow-twitch)
Q.14 The Na+/K+ ATPase pump in muscle fibers helps to:
Release calcium
Maintain resting membrane potential
Hydrolyze ATP for contraction
Generate action potential
Explanation - The Na+/K+ ATPase maintains ion gradients essential for excitability.
Correct answer is: Maintain resting membrane potential
Q.15 Which event occurs first during excitation-contraction coupling?
Calcium release
Action potential in sarcolemma
Cross-bridge formation
ATP hydrolysis
Explanation - Excitation-contraction begins with an action potential spreading across the sarcolemma.
Correct answer is: Action potential in sarcolemma
Q.16 What is rigor mortis caused by?
Excess ATP
Lack of ATP
Excess calcium
Absence of actin
Explanation - In death, ATP depletion prevents cross-bridge detachment, causing rigidity.
Correct answer is: Lack of ATP
Q.17 Which of the following muscles is non-striated?
Skeletal
Cardiac
Smooth
Diaphragm
Explanation - Smooth muscle lacks striations and contracts involuntarily.
Correct answer is: Smooth
Q.18 Which band remains constant during muscle contraction?
A band
I band
H zone
Z disc
Explanation - The A band corresponds to the length of myosin, which doesn’t shorten during contraction.
Correct answer is: A band
Q.19 What is the role of creatine phosphate in muscles?
Forms cross-bridges
Stores calcium
Rapidly regenerates ATP
Breaks down glycogen
Explanation - Creatine phosphate donates phosphate to ADP, rapidly regenerating ATP during high demand.
Correct answer is: Rapidly regenerates ATP
Q.20 Which receptor on skeletal muscle detects acetylcholine?
Nicotinic receptor
Muscarinic receptor
Adrenergic receptor
Serotonin receptor
Explanation - Skeletal muscle contraction is initiated by acetylcholine binding nicotinic receptors.
Correct answer is: Nicotinic receptor
Q.21 In smooth muscle, calcium binds to:
Troponin
Tropomyosin
Calmodulin
Myosin light chain kinase
Explanation - Smooth muscle lacks troponin; calcium binds to calmodulin to activate contraction.
Correct answer is: Calmodulin
Q.22 Which type of contraction occurs when the muscle shortens?
Isometric
Isotonic concentric
Isotonic eccentric
Tetanus
Explanation - In concentric isotonic contraction, the muscle shortens while generating force.
Correct answer is: Isotonic concentric
Q.23 Which ion influx initiates neurotransmitter release at the neuromuscular junction?
Na+
K+
Ca2+
Cl-
Explanation - Calcium influx into the presynaptic terminal triggers acetylcholine release.
Correct answer is: Ca2+
Q.24 Which protein hydrolyzes ATP during contraction?
Actin
Troponin
Myosin
Tropomyosin
Explanation - The myosin head contains ATPase that hydrolyzes ATP for cross-bridge cycling.
Correct answer is: Myosin
Q.25 Which condition results from autoimmune attack on acetylcholine receptors?
Muscular dystrophy
Myasthenia gravis
Tetanus
Botulism
Explanation - Myasthenia gravis is caused by antibodies against nicotinic receptors, impairing muscle activation.
Correct answer is: Myasthenia gravis