Muscle Physiology and Contraction Mechanism

Vocabulary flashcards covering skeletal muscle organization, sarcomere structure, proteins, ATP hydrolysis, cross-bridge cycle, and electrical signal definitions based on Chapter 1 and Chapter 2 notes.

Fascicle

A bundle of muscle fibers contained within a larger muscle structure.

Myofibrils

Tiny bundles within a single muscle fiber cell that consist of a repeated pattern of sarcomeres.

Sarcomere

The structural and functional unit of a myofibril, defined from one Z line to another Z line.

Myosin

The thicker protein filament in a sarcomere with heads that attach to actin during contraction.

Actin

The thinner protein filament in a sarcomere containing binding sites for myosin heads.

I band

The lighter band region in a sarcomere that contains only actin thin filaments.

A band

The darker band region extending from one end of a myosin filament to the other, containing overlapping actin and myosin.

H zone

The zone within the A band that consists strictly of myosin filaments without overlapping actin.

Striations

The striped light and dark appearance of muscle fibers under a microscope caused by the overlap pattern of actin and myosin filaments.

Sarcolemma

The outer lining or cell membrane of a muscle cell.

Sarcoplasm

The fluid space inside the muscle cell.

Multinucleated

A feature of skeletal muscle cells characterized by having multiple nuclei per single cell.

Sarcoplasmic reticulum

A netting structure wrapped around every myofibril that stores and releases calcium required for contraction.

Transverse tubules

Tubular structures that conduct action potential signals deep into the muscle cell to reach the sarcoplasmic reticulum.

Cisternae

Regions of the sarcoplasmic reticulum containing gates that open to release calcium into the sarcoplasm.

Contractile proteins

The group of proteins consisting of actin and myosin that directly create muscle contractions.

Regulatory proteins

The group of proteins consisting of troponin and tropomyosin that regulate when muscle contractions occur.

Tropomyosin

A long rope-like regulatory protein that blocks the binding sites on actin while the muscle is at rest.

Troponin

A regulatory protein attached to tropomyosin that binds calcium, pulling tropomyosin off actin's binding sites.

Titan

The largest structural protein in muscle tissue, responsible for structural stability and recoil elasticity after contraction.

Actinin

A strong structural protein that makes up the Z line and holds adjacent sarcomeres together.

ATPase

An enzyme located on the myosin head that hydrolyzes ATP to release energy.

Hydrolyze

To break down a molecular bond using water, such as breaking ATP down into ADP plus inorganic phosphate.

Cross bridge

The connection established when a energized myosin head binds directly to an exposed site on actin.

Power stroke

The pulling action performed by the myosin head that slides actin filaments toward the center of the sarcomere.

Rigor mortis

Post-mortem muscle stiffness caused by a complete lack of ATP, preventing myosin heads from detaching from actin.

Motor neuron

A neuron that carries action potentials from the central nervous system to a muscle cell to trigger movement.

Polarization

The resting electrical state of a muscle cell when no contraction is taking place.

Depolarization

An electrical signal shift along a cell membrane that activates a muscle cell to contract.

Repolarization

The recovery phase in which a muscle cell returns to its resting polarized state.