Excitation-Contraction Coupling

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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.


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