The Molecular Basis of Muscle Contraction Flashcards
Sliding filament model of muscle contraction
A theory where thick and thin filaments overlap when muscle contracts, with myosin sliding over actin as a result of cross-bridge cycle formation.
Cross-bridge cycle formation
The process that allows muscle cells to contract through the interaction between myosin heads and actin filaments.
Actin filaments
Thin filaments that slide when activated by ATP during muscle contraction.
Myosin
Thick filaments that pull actin filaments towards the center of the sarcomere during muscle contraction.
Sarcoplasmic reticulum (SR)
A structure that stores calcium ions and plays a role in excitation-contraction coupling.
Calcium (Ca2+)
An ion that binds to troponin complex, triggering muscle contraction by allowing myosin heads to bind to actin.
Tropomyosin
A thin filamentous molecule that covers the myosin binding site on actin, preventing interaction between actin and myosin when the muscle is relaxed.
Troponin
A complex with four calcium binding sites that changes conformation when occupied by Ca2+, allowing muscle contraction.
Sarcomere
The basic structural unit of muscle fibers, defined by two adjacent Z discs.
A band
The region of thick filaments in a sarcomere that does not change width during contraction. = overlap of actin and myosin
I band
The region of thin filaments in a sarcomere that shortens when the muscle contracts.
Z discs
Thin dark thread-like lines that define the boundaries of a sarcomere. Shortens during contraction.
Power stroke
The movement of actin towards the center of the sarcomere during the cross-bridge cycle.
ATP hydrolysis
The process that energizes the myosin head to form a cross-bridge with actin.
Calmodulin
A protein that plays a role in the regulation of smooth muscle contraction.
Twitch
A single contraction of a muscle fiber in response to a stimulus.
Summation
The process where the force generated by a motor unit may fuse when a second activation occurs before the muscle relaxes.
H zone
The region in a sarcomere where only thick filaments are present.
Thin filament
Filaments made of actin that interact with thick filaments during muscle contraction.
Thick filament
Filaments made of myosin that pull thin filaments during muscle contraction.
Muscle relaxation
The process where the interaction between actin and myosin is prevented, allowing the muscle to return to its resting state.
Frequency of activation
The rate at which muscle fibers are stimulated, affecting the tension generated.
Fast twitch motor units
Motor units that generate quick, powerful contractions but fatigue rapidly.
Slow twitch motor units
Motor units that generate slower, more sustained contractions and are resistant to fatigue.
Calcium binding sites
Sites on troponin complex that, when occupied by Ca2+, trigger muscle contraction.
Myofilaments
Coherent fibers formed from the interaction between thick and thin filaments.
Muscle cell activation
The process by which a muscle cell is stimulated to contract, involving the binding of calcium to troponin.
Cross-bridge
Formed between myosin heads and actin filaments.
Sarcoplasmic Reticulum (SR)
Releases Ca2+ to initiate muscle contraction.
Acetylcholine (ACh)
Neurotransmitter that stimulates muscle contraction.
Excitation-Contraction Coupling
Process linking muscle stimulation to contraction.
Myosin Light Chain Kinase (MLCK)
Phosphorylates myosin for smooth muscle contraction.
Power Stroke
Myosin pulls actin towards the sarcomere center.
Sliding Filament Model
Describes how thick and thin filaments interact.
Z Discs
Define boundaries of a sarcomere.
Thick Filaments
Composed of myosin, interact with actin.
Thin Filaments
Composed of actin, interact with myosin.
T-tubules
Invaginations of sarcolemma for action potential propagation.
Phosphate (Pi)
Released during cross-bridge formation, strengthens bond.
Skeletal Muscle
Striated muscle under voluntary control.
Smooth Muscle
Non-striated muscle under involuntary control.
Cross-bridge Cycle
Series of steps for muscle contraction.
Neurotransmitter Release
Initiates muscle cell activation at neuromuscular junction.
Action Potential
Electrical signal triggering muscle contraction.
Intracellular Ca2+ Levels
Regulate muscle contraction intensity and duration.
Phosphorylation
Addition of phosphate group, activates myosin.
Calcium Activation
Ca2+ binding leading to muscle contraction.
Sarcoplasmic Reticulum Function
Stores and releases Ca2+ for muscle contraction.
Actin-Myosin Interaction
The protein-to-protein interaction between myosin and actin results in muscle constraction
