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Muscle Structure and Function Quiz

Total questions: 191

Worksheet time: 2hrs 36mins

Name
Class
Date
1.

What is the detailed structure of skeletal muscle, myofibrils, and myofilaments referred to as?

a)

Ultrastructure

b)

Molecular structure

c)

Sliding filament theory

d)

Ratchet mechanism

2.

Which two proteins are primarily involved in the molecular structure of muscle contraction?

a)

Myosin and actin

b)

Tropomyosin and troponin

c)

Collagen and elastin

d)

Keratin and fibrin

3.

What is the basic repeating unit of muscle?

a)

Myofibril

b)

Sarcomere

c)

Actin

d)

Fascia

4.

What does the term "muscle ultrastructure" refer to?

a)

The arrangement of blood vessels in muscles

b)

A complex arrangement of many protein-protein interactions

c)

The structure of muscle fibers only

d)

The organization of fascia in muscles

5.

What is the role of fascia in muscle structure?

a)

It is the basic repeating unit of muscle

b)

It surrounds and supports muscle fibers

c)

It is a type of protein involved in muscle contraction

d)

It is a blood vessel supplying nutrients to muscles

6.

What is the cytoplasmic matrix of a muscle fiber called?

a)

Sarcoplasm

b)

Sarcolemma

c)

Myofibril

d)

Striation

7.

What smaller structures are embedded in the cytoplasmic matrix of a muscle fiber?

a)

Sarcolemma

b)

Sarcoplasm

c)

Myofibrils

d)

Striations

8.

What is the term used for cytosol in muscle fibers?

a)

Myofibril

b)

Sarcoplasm

c)

Sarcolemma

d)

Mitochondria

9.

What is the primary function of transverse tubules (T-tubules) in muscle fibers?

a)

Store calcium

b)

Transmit electrical signals

c)

Produce ATP

d)

Surround myofibrils

10.

What are transverse tubules (T-tubules) made of?

a)

Flattened vesicles

b)

Series of membranous folds extending from the plasma membrane

c)

Glycogen-rich cytosol

d)

Thick and thin filaments

11.

Which structure in the muscle fiber is responsible for storing calcium ions?

a)

Myofibril

b)

Sarcolemma

c)

Sarcoplasmic reticulum

d)

Mitochondria

12.

What is the function of the mitochondria in muscle fibers?

a)

To store calcium ions

b)

To produce energy for muscle contraction

c)

To transmit electrical signals

d)

To form the structural framework of the muscle fiber

13.

What is the diameter of myofibrils?

a)

1 mm

b)

1 μm

c)

10 μm

d)

0.1 μm

14.

What is the basic contractile unit of a muscle fiber?

a)

Myofibril

b)

Sarcomere

c)

Actin

d)

Myosin

15.

Which two main protein filaments are responsible for muscular contraction?

a)

Actin and Myosin

b)

Myosin and Tropomyosin

c)

Actin and Troponin

d)

Myosin and Titin

16.

What is the function of actin and myosin in the sarcomere?

a)

They provide energy for the muscle

b)

They are responsible for muscular contraction

c)

They store calcium ions

d)

They transport oxygen to the muscles

17.

What is the role of the M-line in the sarcomere?

a)

It anchors the thin filaments.

b)

It is the boundary of the sarcomere.

c)

It holds the thick filaments in place.

d)

It contains both thick and thin filaments.

18.

What are the three components that make up the thin filament in muscle structure?

a)

F-actin, tropomyosin, and troponin

b)

Myosin, titin, and nebulin

c)

Tropomyosin, myosin, and titin

d)

Actin, nebulin, and myosin

19.

Which protein molecule in the thin filament is wound into a double helix?

a)

Tropomyosin

b)

F-actin

c)

Troponin

d)

Myosin

20.

What is the role of troponin in the thin filament structure?

a)

It forms the double helix structure of actin.

b)

It lies in the groove of the F-actin helix.

c)

It consists of globular proteins attached to the tropomyosin strand.

d)

It connects actin to myosin filaments.

21.

Which proteins regulate actin in thin filament arrangement?

a)

Tropomyosin and troponin

b)

Myosin and actin

c)

Tropomyosin and myosin

d)

Actin and troponin

22.

What does the TnC protein bind to in the thin filament arrangement?

a)

Tropomyosin

b)

F-actin

c)

Calcium (Ca²⁺) ions

d)

Myosin

23.

What is the approximate number of myosin polypeptides in thick filaments?

a)

100

b)

200

c)

400

d)

600

24.

What do the heads of myosin filaments form when they stick out?

a)

Thick central portion

b)

Cross bridges with actin filaments

c)

Light meromyosin

d)

A-band

25.

What is the function of each myosin head?

a)

Binding to actin and storing energy

b)

Binding to ATP and hydrolyzing it

c)

Forming the tail domain

d)

Regulating light chains

26.

Who independently proposed the sliding filament theory in 1950 to explain how muscle fibers contract?

a)

Albert Einstein and Isaac Newton

b)

A. F. Huxley and H. E. Huxley

c)

Charles Darwin and Gregor Mendel

d)

James Watson and Francis Crick

27.

What happens when the actin and myosin filaments slide between each other?

a)

The muscle relaxes

b)

The muscle contracts

c)

The muscle elongates

d)

The muscle remains stationary

28.

What is the role of cross bridges in the sliding filament theory?

a)

They prevent the actin and myosin filaments from interacting

b)

They facilitate the sliding of actin and myosin filaments past each other

c)

They provide structural support to the sarcomere

d)

They are responsible for muscle relaxation

29.

What is formed between the myosin head and the myosin binding site on the actin filament during contraction?

a)

ATP molecules

b)

Cross-bridges

c)

Actin filaments

d)

Myosin heads

30.

Which step in the powerstroke mechanism involves the movement of the myosin head?

a)

Attachment of myosin

b)

Breaking of actin/myosin interaction

c)

Contraction of the myosin head

d)

Re-attachment further along the actin filament

31.

What is the difference between isometric and isotonic contraction?

a)

Isometric contraction involves movement, while isotonic contraction does not

b)

Isometric contraction involves no change in muscle length, while isotonic contraction involves muscle length change

c)

Isometric contraction is voluntary, while isotonic contraction is involuntary

d)

Isometric contraction occurs in the heart, while isotonic contraction occurs in the skeletal muscles

32.

Which bone is located in the upper arm?

a)

Radius

b)

Ulna

c)

Humerus

d)

Tibia

33.

What is the name of the nerve shown in the diagram?

a)

Ulnar nerve

b)

Biceps nerve

c)

Radius nerve

d)

Ligament nerve

34.

How many bones are muscles usually attached to?

a)

One bone

b)

Two different bones

c)

Three bones

d)

No bones

35.

Which part of the muscle is labeled as "Belly of biceps" in the diagram?

a)

The fixed attachment of the muscle

b)

The middle part of the muscle

c)

The moving attachment of the muscle

d)

The joint of the muscle

36.

How is any movement in the body brought about?

a)

By the relaxation of muscles

b)

By the contraction of a number of muscles working together

c)

By the stretching of muscles

d)

By the expansion of muscles

37.

What is the function of the triceps brachii muscle?

a)

Flexes the elbow

b)

Extends the arm

c)

Rotates the wrist

d)

Moves the fingers

38.

Which joint is located at the shoulder?

a)

Ball and socket joint

b)

Hinge joint

c)

Elbow joint

d)

Wrist joint

39.

What does the term "action is complex" mean in the context of muscle movement?

a)

Only one muscle is involved in movement.

b)

Movement involves many muscles working together.

c)

Flexion and extension are the only actions possible.

d)

Muscles do not play a role in movement.

40.

What is the name of the loose connective tissue sheath that binds each muscle?

a)

Perimysium

b)

Epimysium

c)

Endomysium

d)

Myofibril

41.

What do myofibrils contain?

a)

Tendons

b)

Sarcomeres

c)

Bones

d)

Nerves

42.

Where can cardiac muscles be found in the human body?

a)

Attached to bones

b)

In the walls of the myocardium

c)

In the organs

d)

In the skin

43.

Which type of muscle is found in organs?

a)

Skeletal muscle

b)

Cardiac muscle

c)

Smooth muscle

d)

Bone muscle

44.

What is another name for striated muscle?

a)

Smooth muscle

b)

Cardiac muscle

c)

Striped or skeletal muscle

d)

Involuntary muscle

45.

Which type of muscle is under direct nervous control?

a)

Voluntary muscle

b)

Involuntary muscle

c)

Cardiac muscle

d)

Smooth muscle

46.

What is removed during a muscle biopsy?

a)

A small 'tube' of muscle

b)

A piece of skin

c)

A bone fragment

d)

A blood sample

47.

What shape are the fibers in striated muscle?

a)

Circular

b)

Hexagonal

c)

Triangular

d)

Square

48.

What type of muscle is a cardiac muscle?

a)

Smooth muscle

b)

Striated muscle related to smooth muscle

c)

Skeletal muscle

d)

Voluntary muscle

49.

Is the cardiac muscle voluntary or involuntary?

a)

Voluntary

b)

Involuntary

c)

Both voluntary and involuntary

d)

Neither voluntary nor involuntary

50.

Where are the nuclei located in cardiac muscle cells?

a)

At the edges of the cell

b)

Centrally placed

c)

Scattered randomly

d)

Outside the cell

51.

What is one characteristic of smooth muscle?

a)

It is found in the heart.

b)

It is a high endurance muscle.

c)

It is controlled voluntarily.

d)

It is attached to bones.

52.

Which characteristic is true for smooth muscle tissue?

a)

It has striations.

b)

It has sustained contraction.

c)

It has multiple nuclei per cell.

d)

It is voluntary.

53.

What is a key difference between smooth muscle and skeletal muscle?

a)

Smooth muscle has striations, while skeletal muscle does not.

b)

Smooth muscle has one nucleus per cell, while skeletal muscle has multiple nuclei per cell.

c)

Smooth muscle is voluntary, while skeletal muscle is involuntary.

d)

Smooth muscle is found in the heart, while skeletal muscle is found in the stomach.

54.

What is a motor unit composed of?

a)

A single motor neuron and the group of muscle fibers it innervates

b)

Multiple motor neurons and one muscle fiber

c)

Only muscle fibers

d)

Only motor neurons

55.

Why do some motor neurons innervate more than one muscle fiber?

a)

Because there are fewer muscle fibers than motor neurons

b)

Because there are considerably more muscle fibers than motor neurons

c)

Because motor neurons are larger than muscle fibers

d)

Because muscle fibers are not connected to motor neurons

56.

What part of the motor unit connects to the muscle fibers?

a)

Myofibrils

b)

Branches of motor neurons

c)

Muscle fiber nucleus

d)

Skeletal muscle

57.

Which muscle has the fewest fibres per motor unit?

a)

Eye muscles

b)

Biceps muscles

c)

Larynx muscle

d)

Average body muscles

58.

How many muscle fibres per motor unit are found in the eye muscles?

a)

2-3 fibres/MU

b)

10 fibres/MU

c)

1000+ fibres/MU

d)

150 fibres/MU

59.

What is the average number of muscle fibres per motor unit in the human body?

a)

10 fibres/MU

b)

150 fibres/MU

c)

1000+ fibres/MU

d)

2-3 fibres/MU

60.

What happens when there are fewer muscle fibres per motor unit?

a)

Increased strength

b)

Increased dexterity

c)

Decreased control

d)

Decreased flexibility

61.

Which muscle type is voluntary?

a)

Skeletal

b)

Cardiac

c)

Smooth

d)

Visceral

62.

Which muscle type has high endurance and is involuntary?

a)

Skeletal

b)

Cardiac

c)

Striated

d)

None

63.

Smooth muscle is primarily located in:

a)

Bones

b)

Heart

c)

Digestive tract & vessels

d)

Skin

64.

Skeletal muscles make up approximately what percentage of body mass?

a)

20%

b)

40%

c)

60%

d)

70%

65.

How many skeletal muscles exist in the human body?

a)

150

b)

300

c)

650

d)

1000

66.

What attaches muscle to bone?

a)

Ligament

b)

Cartilage

c)

Tendon

d)

Fascia

67.

What attaches bone to bone?

a)

Tendon

b)

Ligament

c)

Fascia

d)

Epimysium

68.

The fixed attachment of a muscle is known as the:

a)

Insertion

b)

Origin

c)

Anchor

69.

Muscles can only:

a)

Push

b)

Pull

c)

Twist

d)

Vibrate

70.

Flexors function to:

a)

Open a joint

b)

Close a joint

c)

Rotate a joint

d)

Immobilize a joint

71.

Extensors function to:

a)

Open a joint

b)

Close a joint

c)

Rotate a joint

d)

Lock a joint

72.

12. Biceps brachii primarily:

a)

Extends the elbow

b)

Flexes the elbow

c)

Rotates the wrist

d)

Flexes the shoulder

73.

Triceps brachii primarily:

a)

Flexes elbow

b)

Extends elbow

c)

Flexes wrist

d)

Supinates hand

74.

The connective tissue surrounding an entire muscle is:

a)

Endomysium

b)

Perimysium

c)

Epimysium

d)

Sarcolemma

75.

A fascicle is a bundle of:

a)

Myofibrils

b)

Fibers

c)

Filaments

d)

Cells only

76.

Myofibrils contain the contractile unit known as:

a)

Actin

b)

Sarcomere

c)

Myosin

d)

Endomysium

77.

Cardiac muscle contains:

a)

Peripheral nuclei

b)

Multiple nuclei

c)

1-2 centrally located nuclei

d)

No nuclei

78.

Cardiac muscle contains unique structures called:

a)

Nodes

b)

Intercalated discs

c)

Sarcomeres only

d)

Gap fibers

79.

Smooth muscle cells contain how many nuclei?

a)

Many

b)

None

c)

1 central nucleus

d)

2 peripheral nuclei

80.

Smooth muscle contraction is generally:

a)

Short and weak

b)

Sustained

c)

Voluntary

d)

Uncoordinated

81.

The functional unit of muscle activity is the:

a)

Muscle

b)

Sarcomere

c)

Motor unit

d)

Myofibril

82.

A motor unit includes:

a)

Motor neuron only

b)

Muscle fibers only

c)

Motor neuron + fibers it innervates

d)

Spinal cord

83.

Smaller motor units allow:

a)

Less control

b)

More precise control

c)

Random contraction

84.

Which muscle has the fewest fibers per motor unit?

a)

Biceps

b)

Larynx

c)

Quadriceps

d)

Gastrocnemius

85.

The average number of fibers per motor unit is:

a)

10

b)

100

c)

150

d)

1000

86.

The neuromuscular junction is also called:

a)

Motor plate

b)

Motor endplate

c)

Myoneural disc

d)

Muscle receptor

87.

The muscle response to a single stimulus is a:

a)

Spasm

b)

Twitch

c)

Tetany

d)

Cramp

88.

The latent period of a twitch lasts approximately:

a)

0.005 sec

b)

0.04 sec

c)

0.05 sec

d)

1 sec

89.

The contraction period lasts:

a)

0.005 sec

b)

0.04 sec

c)

0.05 sec

d)

1 sec

90.

The relaxation period lasts:

a)

0.005 sec

b)

0.04 sec

c)

0.05 sec

d)

1 sec

91.

A stimulus during the refractory period produces:

a)

Stronger contraction

b)

Weaker contraction

c)

No response

d)

Tetany

92.

Summation of contraction occurs when:

a)

Muscle relaxes

b)

Second stimulus arrives before relaxation

c)

Low-frequency firing

d)

Fiber fatigues

93.

Increasing the number of motor units firing is:

a)

Twitching

b)

Recruitment

c)

Tetany

d)

Fatigue

94.

Increasing the stimulus frequency leads to:

a)

Wave summation

b)

Relaxation

c)

Cramping

d)

Inhibition

95.

Sustained maximal contraction is called:

a)

Wave summation

b)

Tetany

c)

Twitching

d)

Fatigue

96.

Isometric contraction means:

a)

Same tension

b)

Same length

c)

Changing tension

d)

Changing length

97.

In isometric contraction, the muscle:

a)

Shortens

b)

Lengthens

c)

Stays same length

d)

Melts

98.

Isotonic contraction means:

a)

Same tension

b)

Same length

c)

Changing tension

d)

Changing length

99.

Concentric contraction means muscle:

a)

Lengthens

b)

Shortens

c)

Stays same

d)

Trembles

100.

Eccentric contraction means muscle:

a)

Shortens

b)

Remains still

c)

Lengthens

d)

Contracts isometrically

101.

Eccentric contractions often cause:

a)

Less damage

b)

More muscle damage

c)

No effect

d)

Instant fatigue

102.

During eccentric contraction, force is:

a)

Greater than load

b)

Less than load

c)

Same as load

d)

Not measurable

103.

Muscles are stronger in which contraction?

a)

Concentric

b)

Isometric

c)

Eccentric

d)

None

104.

Tetanus occurs at frequencies above:

a)

5 pulses/sec

b)

10 pulses/sec

c)

20 pulses/sec

d)

40 pulses/sec

105.

Which muscle type is voluntary?

a)

Skeletal

b)

Cardiac

c)

Smooth

d)

Visceral

106.

Which membrane encloses an individual muscle fiber?

a)

Endomysium

b)

Sarcolemma

c)

Sarcoplasm

d)

Perimysium

e)

Plasmalemma

107.

Which of the following is rich in glycogen, ATP and creatine phosphate within muscle?

a)

Sarcoplasmic reticulum

b)

Sarcolemma

c)

Sarcoplasm

d)

Endomysium

e)

T-tubule

108.

What is the primary role of T-tubules in muscle fibers?

a)

Store calcium

b)

Synthesize ATP

c)

Anchor myofilaments

d)

Transmit electrical signals inward

e)

Produce acetylcholine

109.

What is the main function of the sarcoplasmic reticulum (SR)?

a)

Sequester (store) calcium

b)

Produce acetylcholine

c)

Generate action potentials

d)

Form the Z-line

e)

Synthesize tropomyosin

110.

What structural unit is formed by a T-tubule plus two adjacent terminal cisternae?

a)

A. Sarcomere

b)

B. Myofibril

c)

C. Triad

d)

D. Motor unit

e)

E. Neuromuscular junction

111.

Approximately how wide are myofibrils?

a)

1 μm

b)

10 μm

c)

0.1 μm

d)

5 μm

e)

100 nm

112.

Which band is the light (isotropic) band of the sarcomere?

a)

A-band

b)

I-band

c)

H-zone

d)

M-line

e)

Z-disc

113.

Which band corresponds to the dark (anisotropic) region of the sarcomere?

a)

A-band

b)

I-band

c)

Z-line

d)

H-zone

e)

M-line

114.

What is found in the middle of the I-band?

a)

A-band

b)

H-zone

c)

Z-line (Z-disc)

d)

M-line

e)

T-tubule

115.

Which band corresponds to the region containing only thick filaments when muscle is relaxed?

a)

A. I-band

b)

B. A-band

c)

C. H-zone

d)

D. Z-line

e)

E. M-line

116.

Which band contains both thin and thick filaments overlapping?

a)

I-band

b)

H-zone

c)

A-band

d)

Z-line

e)

T-tubule

117.

What structural feature runs between Z-lines defining the sarcomere boundary?

a)

M-line

b)

H-zone

c)

A-band

d)

Sarcomere extends between Z-lines

e)

Triad

118.

What is the basic repeating unit of a muscle fiber?

a)

Sarcomere

b)

Myofibril

c)

Myofilament

d)

Sarcoplasm

e)

Sarcolemma

119.

What is the basic repeating unit of a muscle fiber?

a)

Sarcomere

b)

Myofibril

c)

Myofilament

d)

Sarcoplasm

120.

Which filament is referred to as the thin filament?

a)

Myosin

b)

Actin

c)

Titin

d)

Nebulin

e)

Myomesin

121.

What two filaments give skeletal muscle its striated appearance?

a)

A. Titin and nebulin

b)

B. Troponin and tropomyosin

c)

C. T-tubules and SR

d)

D. Actin (thin) and myosin (thick)

e)

E. Myomesin and desmin

122.

Which three components make up the thin filament?

a)

A. F-actin, tropomyosin, troponin

b)

B. Myosin, titin, nebulin

c)

C. Actinin, myomesin, desmin

d)

D. TnC, TnI, TnT only

e)

E. Actin, myosin, tropomyosin

123.

Which component of the thin filament is an α-helical protein lying in the groove of F-actin?

a)

Troponin

b)

Tropomyosin

c)

TnC

d)

Nebulin

e)

Titin

124.

Which proteins are mentioned as associated with thin filament structure in the images (besides actin)?

a)

Myomesin and desmin

b)

Titin only

c)

Titin and nebulin

d)

Dystrophin and dystroglycan

e)

Myosin and actinin

125.

Which structure contains the actin-binding sites covered by tropomyosin?

a)

Myosin head

b)

F-actin (thin filament)

c)

Sarcoplasmic reticulum

d)

T-tubule

e)

M-line

126.

E. Sarcolemma

a)

Sarcolemma

b)

Myofibril

c)

Endomysium

d)

Perimysium

127.

Which troponin subunit binds calcium?

a)

TnT

b)

TnI

c)

TnM

d)

TnC

e)

TnA

128.

In the resting state, what covers the myosin-binding sites on actin?

a)

Troponin C

b)

Tropomyosin

c)

Myosin heads

d)

Titin

e)

Nebulin

129.

Which protein binds to tropomyosin as part of the troponin complex?

a)

TnC

b)

TnT

c)

TnI

d)

TnX

e)

TnM

130.

Which troponin subunit binds directly to actin in the thin filament?

a)

TnI

b)

TnT

c)

TnC

d)

TnA

e)

TnB

131.

What is the role of troponin I (TnI) in the thin filament?

a)

Bind Ca2+

b)

Bind tropomyosin

c)

Bind myosin

d)

Bind to F-actin and help inhibit interaction in resting state

e)

Hydrolyse ATP

132.

Which protein is primarily responsible for blocking myosin binding sites on actin at rest?

a)

TnC

b)

Tropomyosin

c)

Myosin regulatory light chain

d)

Titin

e)

Myomesin

133.

What event exposes the myosin binding site on actin during contraction?

a)

ATP binding to myosin

b)

Phosphate release from myosin

c)

Ca2+ binding to TnC

d)

Phosphate release from actin

134.

Which molecule is the direct trigger for conformational change in tropomyosin to expose actin sites?

a)

ATP

b)

ADP

c)

Ca2+

d)

Na+

e)

Acetylcholine

135.

Which of the following is an effect of troponin TnC binding Ca2+?

a)

A. Inhibition of ATP hydrolysis

b)

B. Blocking of actin-myosin binding

c)

C. Collapse of the sarcomere

d)

D. Conformational change in troponin-tropomyosin exposing active sites

e)

E. Breakdown of tropomyosin

136.

What happens to tropomyosin when Ca2+ concentration rises in the sarcoplasm?

a)

It binds more tightly to actin and prevents binding

b)

It shifts position to uncover myosin-binding sites

c)

It hydrolyses ATP

d)

It forms cross-bridges with myosin

e)

It degrades

137.

Approximately how many myosin polypeptides make up a myosin filament?

a)

About 400

b)

About 40

c)

About 4,000

d)

About 40,000

e)

About 100

138.

Which region of myosin packs together to form the thick central portion of the filament?

a)

Head region

b)

Tail (coiled-coil) region

c)

S1 fragment only

d)

Neck light chain

e)

ATP-binding loop

139.

Which protein forms most of the tail region (light meromyosin) of myosin?

a)

Light meromyosin composes most of the tail

b)

Heavy meromyosin composes most of the tail

c)

S1 fragment is the tail

d)

TnT forms the tail

140.

Which part of the myosin molecule binds and hydrolyses ATP?

a)

A. Tail

b)

B. Light meromyosin

c)

C. Head

d)

D. Titin-binding domain

e)

E. Tail coiled-coil

141.

What energy form is stored on the myosin head after ATP hydrolysis?

a)

ATP

b)

ADP + inorganic phosphate (Pi)

c)

cAMP

d)

Creatine phosphate

e)

Glucose-6-phosphate

142.

Where are the myosin heads located on the molecule?

a)

In the tail region only

b)

Evenly along the tail

c)

At the N-terminal parts of the heavy chains (head region)

d)

At the C-terminal tail only

e)

On titin

143.

Which fragment corresponds to the active head portion of myosin often studied in experiments?

a)

LMM (light meromyosin)

b)

Tail fragment

c)

Neck fragment

d)

S1 fragment

e)

C-terminal fragment

144.

Which light chains are found on the myosin neck region?

a)

Essential and regulatory light chains

b)

Actin and myosin light chains

c)

Troponin light chains

d)

Titin light chains

e)

Myomesin light chains

145.

What structural feature gives the myosin tail its rod-shaped character?

a)

Beta-sheet stacking

b)

Coiled-coil α-helical rod formed by heavy chains

c)

Triple helix collagen-like motif

d)

Microtubule binding

e)

Actin-binding repeats

146.

Which of the following best describes the functional role of the myosin head?

a)

Only structural support

b)

Binds actin and hydrolyses ATP to generate force

c)

Stores calcium

d)

Forms the Z-line

e)

Forms the sarcolemma

147.

Who proposed the sliding filament theory around 1950?

a)

Huxley only

b)

Huxley and Hill

c)

Debrunner and Huxley

d)

A. F. Huxley and H. E. Huxley

e)

Bernard and Huxley

148.

According to the sliding filament theory, how do myosin filaments produce contraction?

a)

Myosin heads walk along actin using ATP

b)

Actin filaments shorten chemically

c)

Sarcolemma constriction pulls filaments

d)

Calcium breaks down actin

e)

ATP polymerizes actin

149.

Which of the following best describes the force of contraction according to the sliding filament theory?

a)

Caused by movement of cross-bridges (myosin heads)

b)

Generated by ATP hydrolysis in mitochondria exclusively

c)

Result of calcium binding to ACh receptors

d)

Due to the elongation of actin filaments

e)

Due to increased sarcoplasmic volume

150.

What is the first step in the sliding filament contraction cycle once a nerve signal arrives?

a)

ATP binds myosin causing detachment

b)

Calcium is released from the SR exposing binding sites

c)

ADP is released from myosin

d)

Tropomyosin binds more tightly

e)

Actin polymerizes

151.

Release of which molecule from myosin initiates the power stroke?

a)

ATP

b)

Water (H2O)

c)

ADP

d)

Calcium

e)

Creatine phosphate

152.

What causes the separation (detachment) of the actin-myosin cross-bridge?

a)

Binding of a new ATP molecule to the myosin head

b)

Calcium binding to troponin

c)

ADP release from myosin

d)

Actin polymerization

e)

Sarcolemma depolarization

153.

Select the correct answer.

a)

Binding of Ca2+ to TnC

b)

Release of inorganic phosphate

c)

Hydrolysis of ATP to ADP + Pi

d)

Oxidation of ADP

154.

Which event describes the 'cocking' of the myosin head?

a)

ADP release

b)

Powerstroke

c)

Hydrolysis of ATP to ADP + Pi which reorients the head

d)

Binding of actin to tropomyosin

e)

Calcium uptake by SR

155.

What is the immediate consequence of ATP binding to the myosin head in the cross-bridge cycle?

a)

Powerstroke

b)

Release of Pi only

c)

Calcium release

d)

Tropomyosin movement

e)

Detachment of myosin from actin

156.

Which of these is a correct sequence in the contraction cycle?

a)

ATP binds → Pi release → Ca2+ release

b)

ADP release → Pi release → Ca2+ binding

c)

Ca2+ binding → cross-bridge formation → Pi release → ADP release (powerstroke)

d)

Tropomyosin covers site → ATP binds → muscle contracts

e)

Acetylcholine reuptake → contraction → Ca2+ release

157.

Which event directly follows the powerstroke in the cross-bridge cycle?

a)

Ca2+ reuptake into SR

b)

Formation of new actin monomers

c)

TnC releases Ca2+

d)

Binding of ATP to myosin causing detachment from actin

e)

Hydrolysis of ATP to ADP + Pi without detachment

158.

Which statement correctly describes the sequence when ATP is hydrolyzed on the myosin head?

a)

Hydrolysis immediately detaches myosin from actin

b)

Hydrolysis to ADP + Pi energizes (cocks) the head ready to bind actin

c)

Hydrolysis occurs after detachment of tropomyosin

d)

Hydrolysis causes permanent binding to actin

e)

Hydrolysis produces glucose

159.

Which molecule must be present for cross-bridge cycling to continue?

a)

ATP

b)

Glucose only

160.

What happens to filament overlap during contraction?

a)

Overlap between actin and myosin increases

b)

Overlap decreases

c)

Overlap stays the same

d)

Myosin dissociates completely

e)

Actin shortens chemically

161.

Which statement about the sliding filament theory diagrams is correct?

a)

They show actin shortening chemically

b)

They show A-band length decreasing

c)

They show increased overlap between filaments during contraction

d)

They depict the sarcolemma as the force source

e)

They indicate myosin dissolving during contraction

162.

Which sarcomere band remains constant in length during contraction?

a)

I-band

b)

A-band

c)

H-zone

d)

Z-line

e)

M-line

163.

Which sarcomere region shortens during muscle contraction?

a)

A. I-band

b)

B. A-band

c)

C. M-line

d)

D. T-tubule

e)

E. SR terminal cisternae

164.

What happens to the H-zone during contraction?

a)

It lengthens

b)

It doubles in width

c)

It is reduced or disappears

d)

It becomes more electron-dense

e)

It forms new Z-lines

165.

Which statement about the A-band during contraction is correct?

a)

A. A-band length remains constant

b)

B. A-band shortens

c)

C. A-band disappears

d)

D. A-band doubles in length

e)

E. A-band becomes the I-band

166.

Which of the following is TRUE about the sarcomere during contraction?

a)

Both A-band and I-band lengthen

b)

A-band shortens while I-band remains same

c)

I-band shortens while A-band remains constant

d)

H-zone enlarges

e)

Z-lines move apart

167.

What does the ratchet mechanism of contraction describe?

a)

Action potential propagation along nerves

b)

Biochemical and biophysical events converting ATP energy into displacement of filaments

c)

Passive stretching of muscle

d)

Mitochondrial ATP production only

e)

Neurotransmitter recycling

168.

Which of these is NOT a step of the cross-bridge (powerstroke) action listed in the slides?

a)

A. Attachment of myosin

b)

B. Contraction of myosin head

c)

C. Breaking of actin/myosin interaction

d)

D. Synthesis of actin monomers

e)

E. Re-attachment further along actin

169.

What chemical reaction in the myosin head provides the energy for conformational change?

a)

ATP → ADP + Pi + Energy

b)

ADP → ATP + Pi

c)

Glucose → Pyruvate

d)

Creatine → Creatine phosphate

e)

GTP hydrolysis

170.

Approximately how far does the powerstroke move the actin filament towards the M-line?

a)

0.5–1 nm

b)

5–12 nm

c)

50–100 nm

d)

100–200 nm

e)

20–30 nm

171.

Which of the following best characterizes the powerstroke?

a)

Change in myosin head conformation that pulls actin toward the M-line

b)

Synthesis of ATP on the myosin head

c)

Release of Ca2+ from SR

d)

Polymerization of actin

e)

Uptake of Na+ into the SR

172.

How many ATP molecules are used per myosin head for each powerstroke?

a)

1

b)

2

c)

3

d)

4

e)

5

173.

How many ATP molecules are used per myosin head for each powerstroke?

a)

One ATP molecule

b)

Two ATP molecules

c)

Zero ATP molecules

d)

Variable: 0-3 ATP

e)

Four ATP molecules

174.

What is true about ADP + Pi release from myosin when actin is absent?

a)

Release is faster without actin

b)

ADP + Pi cannot be released at all

c)

Release is slow without actin

d)

Release is independent of actin

e)

ADP is immediately converted to ATP

175.

What describes the cyclical depiction of events in the myosin head?

a)

A linear one-time reaction

b)

A repetitive cycle of binding, powerstroke, detachment and re-cocking

c)

An irreversible collapse

d)

A single-step detachment

e)

A process independent of ATP

176.

In resting muscle, what form are most myosin heads in?

a)

Myosin-ATP

b)

Myosin-ADP-Pi

c)

Myosin-ADP only

d)

Free myosin monomers

e)

Actomyosin complex

177.

Which event is the first listed step in the detailed ratchet mechanism on the slide?

a)

A. Actin is uncovered when Ca2+ binds troponin

b)

B. ATP binds myosin and causes detachment

c)

C. ADP is released from myosin

d)

D. Actin is cleaved

e)

E. Myosin dissociates into monomers

178.

What forms when ATP replaces ADP on the myosin head while it is bound to actin?

a)

Myosin-ADP only

b)

Myosin-Pi

c)

Myosin-actin-ADP

d)

Actomyosin-ATP (A-M-ATP) complex

e)

Titin-actin complex

179.

What occurs immediately after phosphate (Pi) is released from myosin bound to actin?

a)

ATP binds and detaches myosin

b)

Calcium is pumped back into SR

c)

The powerstroke occurs as the myosin head changes conformation

180.

Which term describes the complex formed when ATP replaces ADP in the myosin head while still associated with actin?

a)

Myosin-ADP

b)

A-M-ATP (actomyosin-ATP) complex

c)

Myosin-Pi complex

d)

Tropomyosin-actin complex

e)

Crosslink complex

181.

What best defines excitation-contraction coupling (ECC)?

a)

Synthesis of actin and myosin

b)

Rapid communication between membrane electrical events and Ca2+ release leading to contraction

c)

The sliding of filaments past each other

d)

Reuptake of calcium into the SR

e)

Neurotransmitter synthesis in the motor neuron

182.

How does the depolarization travel into the interior of the muscle fiber?

a)

Via the T-tubule system

b)

Via the SR only

c)

By diffusion of calcium

d)

Through gap junctions

e)

Along collagen fibers

183.

Which structure releases Ca2+ into the sarcoplasm in response to the T-tubule depolarization?

a)

Mitochondria

b)

Golgi apparatus

c)

Sarcoplasmic reticulum (terminal cisternae)

d)

Nucleus

e)

Endoplasmic reticulum of adjacent cells

184.

Which structure transmits action potentials into the interior of the muscle fiber to trigger Ca2+ release?

a)

T-tubules

b)

SR terminal cisternae

c)

Mitochondria

d)

Endomysium

e)

Sarcomere

185.

Which structure is directly adjacent to T-tubules and releases calcium during ECC?

a)

Terminal cisternae of the sarcoplasmic reticulum

b)

Nucleus

c)

Mitochondrion

d)

Golgi apparatus

e)

Endomysium

186.

What is the initial chemical released at the neuromuscular junction to trigger muscle contraction?

a)

Dopamine

b)

Acetylcholine (ACh)

c)

Serotonin

d)

Glutamate

e)

GABA

187.

What role does acetylcholine (ACh) play at the neuromuscular junction?

a)

It is released from the nerve terminal to depolarize the sarcolemma

b)

It stores calcium in the SR

c)

It binds troponin directly

d)

It hydrolyzes ATP

e)

It blocks T-tubules

188.

What effect does Ca2+ binding to TnC have on TnI and tropomyosin?

a)

TnI disengages from actin causing tropomyosin to uncover active sites

b)

TnI binds more tightly to actin preventing contraction

c)

Tropomyosin binds to myosin

d)

TnT releases ATP

e)

TnC hydrolyzes ATP

189.

How is Ca2+ removed from the myofiber to allow muscle relaxation?

a)

Diffusion into extracellular space

b)

Binding permanently to troponin

c)

Active pumping back into the sarcoplasmic reticulum

d)

Conversion into ATP

e)

Sequestration by mitochondria permanently

190.

What is the consequence of pumping Ca2+ back into the SR?

a)

Muscle relaxes

b)

Muscle contracts further

c)

More cross-bridges form

d)

A-band shortens

e)

ATP is synthesized

191.

What is the fate of Ca2+ after muscle contraction to restore the resting state?

a)

It diffuses out through the sarcolemma

b)

It is bound permanently to troponin

c)

It is actively pumped back into the SR

d)

It is converted to Mg2+

e)

It is exocytosed