Excitation-Contraction Coupling
Elasticity
Ability of muscle to recoil to its original resting length after being stretched.
Contractility
Ability of muscle to shorten with force.
Extensibility
Ability of muscle to stretch beyond its normal resting length.
Presynaptic Terminal
Axon terminal of motor neuron that releases neurotransmitter.
Sarcomere
Basic functional unit of muscle fiber where muscle contraction occurs.
Excitability
Capacity of muscle to respond to a stimulus.
Depolarization
Change in membrane potential towards positive, triggering action potential.
Calcium Channels
Channels on SR terminal cisternae that open to allow calcium into sarcoplasm.
Fast-Twitch Muscle Fibers
Contract rapidly, fatigue more quickly, less myoglobin.
Slow-Twitch Muscle Fibers
Contract slowly, fatigue-resistant, rich in myoglobin.
Sarcoplasm
Cytoplasm of muscle fiber.
A Band
Dark-staining region of sarcomere containing overlapping actin and myosin myofilaments.
Atrophy
Decrease in muscle size due to disuse or disease.
Action Potential
Electrical signal that triggers muscle contraction.
T Tubules
Extensions of sarcolemma that carry action potentials into muscle fiber.
Z Disk
Filamentous network of protein that serves as attachment for actin myofilaments.
All-or-None Principle
If threshold is reached, muscle fiber will respond completely with action potential.
Hypertrophy
Increase in muscle size due to increase in myofibrils and nuclei.
I Band
Lighter-staining region of sarcomere containing actin myofilaments.
Postsynaptic Membrane
Membrane of muscle fiber that responds to neurotransmitter.
M Line
Middle of H zone, holding myosin in place.
ATP
Molecule broken down by myosin head to provide energy for muscle contraction.
Eccentric Contraction
Muscle lengthens while generating force.
Concentric Contraction
Muscle shortens while generating force.
Motor Neuron
Neuron that stimulates muscle contraction through action potentials.
Acetylcholine
Neurotransmitter released at neuromuscular junction to stimulate muscle contraction.
Sarcolemma
Plasma membrane of muscle fiber.
Neuromuscular Junction
Point of contact between motor neuron and muscle fiber.
Excitation-Contraction Coupling
Process linking electrical and mechanical components of muscle contraction.
Cross-Bridge Movement
Process of myosin heads binding to active sites on actin and causing muscle contraction.
Recovery Stroke
Process that returns myosin head to high-energy position after power stroke.
Troponin
Protein that binds calcium and initiates muscle contraction.
Ion Channels
Proteins that open and close in response to voltage or ligand binding.
Power Stroke
Rapid movement of myosin heads that pulls actin myofilament towards H zone.
H Zone
Region in A band where actin and myosin do not overlap.
Repolarization
Return of membrane potential to resting state after depolarization.
Synaptic Cleft
Space between presynaptic terminal and postsynaptic membrane.
Action Potential Propagation
Spreading of action potential along plasma membrane of muscle fiber.
Resting Membrane Potential
Voltage difference across plasma membrane of muscle fiber at rest.