The Molecular Basis of Muscle Contraction

Question 1

Sliding filament model of muscle contraction

Answer 1

A theory where thick and thin filaments overlap when muscle contracts, with myosin sliding over actin as a result of cross-bridge cycle formation.

Question 2

Cross-bridge cycle formation

Answer 2

The process that allows muscle cells to contract through the interaction between myosin heads and actin filaments.

Question 3

Actin filaments

Answer 3

Thin filaments that slide when activated by ATP during muscle contraction.

Question 4

Myosin

Answer 4

Thick filaments that pull actin filaments towards the center of the sarcomere during muscle contraction.

Question 5

Sarcoplasmic reticulum (SR)

Answer 5

A structure that stores calcium ions and plays a role in excitation-contraction coupling.

Question 6

Calcium (Ca2+)

Answer 6

An ion that binds to troponin complex, triggering muscle contraction by allowing myosin heads to bind to actin.

Question 7

Tropomyosin

Answer 7

A thin filamentous molecule that covers the myosin binding site on actin, preventing interaction between actin and myosin when the muscle is relaxed.

Question 8

Troponin

Answer 8

A complex with four calcium binding sites that changes conformation when occupied by Ca2+, allowing muscle contraction.

Question 9

Sarcomere

Answer 9

The basic structural unit of muscle fibers, defined by two adjacent Z discs.

Question 10

A band

Answer 10

The region of thick filaments in a sarcomere that does not change width during contraction. = overlap of actin and myosin

Question 11

I band

Answer 11

The region of thin filaments in a sarcomere that shortens when the muscle contracts.

Question 12

Z discs

Answer 12

Thin dark thread-like lines that define the boundaries of a sarcomere. Shortens during contraction.

Question 13

Power stroke

Answer 13

The movement of actin towards the center of the sarcomere during the cross-bridge cycle.

Question 14

ATP hydrolysis

Answer 14

The process that energizes the myosin head to form a cross-bridge with actin.

Question 15

Calmodulin

Answer 15

A protein that plays a role in the regulation of smooth muscle contraction.

Question 16

Twitch

Answer 16

A single contraction of a muscle fiber in response to a stimulus.

Question 17

Summation

Answer 17

The process where the force generated by a motor unit may fuse when a second activation occurs before the muscle relaxes.

Question 18

H zone

Answer 18

The region in a sarcomere where only thick filaments are present.

Question 19

Thin filament

Answer 19

Filaments made of actin that interact with thick filaments during muscle contraction.

Question 20

Thick filament

Answer 20

Filaments made of myosin that pull thin filaments during muscle contraction.

Question 21

Muscle relaxation

Answer 21

The process where the interaction between actin and myosin is prevented, allowing the muscle to return to its resting state.

Question 22

Frequency of activation

Answer 22

The rate at which muscle fibers are stimulated, affecting the tension generated.

Question 23

Fast twitch motor units

Answer 23

Motor units that generate quick, powerful contractions but fatigue rapidly.

Question 24

Slow twitch motor units

Answer 24

Motor units that generate slower, more sustained contractions and are resistant to fatigue.

Question 25

Calcium binding sites

Answer 25

Sites on troponin complex that, when occupied by Ca2+, trigger muscle contraction.

Question 26

Myofilaments

Answer 26

Coherent fibers formed from the interaction between thick and thin filaments.

Question 27

Muscle cell activation

Answer 27

The process by which a muscle cell is stimulated to contract, involving the binding of calcium to troponin.

Question 28

Cross-bridge

Answer 28

Formed between myosin heads and actin filaments.

Question 29

Sarcoplasmic Reticulum (SR)

Answer 29

Releases Ca2+ to initiate muscle contraction.

Question 30

Acetylcholine (ACh)

Answer 30

Neurotransmitter that stimulates muscle contraction.

Question 31

Excitation-Contraction Coupling

Answer 31

Process linking muscle stimulation to contraction.

Question 32

Myosin Light Chain Kinase (MLCK)

Answer 32

Phosphorylates myosin for smooth muscle contraction.

Question 33

Power Stroke

Answer 33

Myosin pulls actin towards the sarcomere center.

Question 34

Sliding Filament Model

Answer 34

Describes how thick and thin filaments interact.

Question 35

Z Discs

Answer 35

Define boundaries of a sarcomere.

Question 36

Thick Filaments

Answer 36

Composed of myosin, interact with actin.

Question 37

Thin Filaments

Answer 37

Composed of actin, interact with myosin.

Question 38

T-tubules

Answer 38

Invaginations of sarcolemma for action potential propagation.

Question 39

Phosphate (Pi)

Answer 39

Released during cross-bridge formation, strengthens bond.

Question 40

Skeletal Muscle

Answer 40

Striated muscle under voluntary control.

Question 41

Smooth Muscle

Answer 41

Non-striated muscle under involuntary control.

Question 42

Cross-bridge Cycle

Answer 42

Series of steps for muscle contraction.

Question 43

Neurotransmitter Release

Answer 43

Initiates muscle cell activation at neuromuscular junction.

Question 44

Action Potential

Answer 44

Electrical signal triggering muscle contraction.

Question 45

Intracellular Ca2+ Levels

Answer 45

Regulate muscle contraction intensity and duration.

Question 46

Phosphorylation

Answer 46

Addition of phosphate group, activates myosin.

Question 47

Calcium Activation

Answer 47

Ca2+ binding leading to muscle contraction.

Question 48

Sarcoplasmic Reticulum Function

Answer 48

Stores and releases Ca2+ for muscle contraction.

Question 49

Actin-Myosin Interaction

Answer 49

The protein-to-protein interaction between myosin and actin results in muscle constraction