help define these pls

Z-line

The boundary structure in a muscle sarcomere that separates individual sarcomeres and anchors thin filaments.

G actin

Globular protein that polymerizes to form F actin in muscle fibers.

F actin

Fibrous protein that forms the main component of thin filaments in muscle fibers.

Troponin

A complex of three proteins that binds calcium ions and regulates muscle contraction by controlling the position of tropomyosin.

Tropomyosin

A protein that wraps around actin filaments and blocks myosin binding sites in the absence of calcium.

Myofilament

A protein filament (actin or myosin) that is part of the structure of myofibrils in muscle fibers.

Intercalated disc

Specialized connections between cardiac muscle cells that facilitate synchronized contraction.

Sarcolemma

The plasma membrane of a muscle cell.

Sarcoplasmic reticulum

A specialized endoplasmic reticulum in muscle cells that stores calcium ions.

Myofibril

A long, filamentous organelle found within muscle cells composed of myofilaments.

Fascicle

A bundle of muscle fibers (muscle cells) surrounded by a connective tissue sheath.

Thin filament

The filament primarily composed of actin, troponin, and tropomyosin; responsible for muscle contraction.

Thick filament

The filament primarily composed of myosin that interacts with thin filaments to facilitate muscle contraction.

T-tubules

Transverse tubules that extend into muscle fibers and facilitate the spread of action potentials.