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Muscles
Structural Components of a Muscle Fiber
27
Anatomy
Undergraduate 4
10/10/2007

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Term
Sarcolemma
Definition
The plasma membrane of a muscle fiber
Term
Sarcoplasm
Definition
The cytoplasm of a muscle fiber
Term
Glycogen
Definition

An energy-storage polysaccharide abundant in muscle

Term
Myoglobin
Definition
An oxygen-storing red pigment of muscle
Term
T tubule
Definition
A tunnel-like extension of the sarcolemma extending from one side of the muscle fiber to the other; conveys electrical signals from the cell surface to its interior
Term
Sarcoplasmic reticulum
Definition
The smooth ER of a muscle fiber; a Ca2+ reservoir
Term
Terminal cisternae
Definition
The dilated ends of sarcoplasmic reticulum adjacent to a T tubule
Term
Myofibrils
Definition
A bundle of protein microfilaments (myofilaments)
Term
Myofilament
Definition
A threadlike complex of several hundred contractile protein molecules
Term
Thick filament
Definition
A myofilament about 11 nm in diameter composed of bundled myosin molecules
Term
Elastic filament
Definition
A myofilament about 1 nm in diameter composed of a giant protein, titin, that flanks a thick filament and anchors it to a Z disc; stabilizes and centers the thick filament and prevents overstretching
Term
Thin filament
Definition
A myofilament about 5 to 6 nm in diameter composed of actic, toponin, and tropomyosin
Term
Myosin
Definition
A protein with a long shaftlike tail and a globular head; constitutes the thick myofilament
Term
F actin
Definition
A fibrous protein made of a long chain of G actin molecules twisted into a helix; main protein of the thin myofilament
Term
G actin
Definition
A globular subunit of F actin with an active site for binding a myosin head
Term
Regulatory proteins
Definition
Troponin and tropomyosin, proteins that do not directly engage in the sliding filament process of muscle contraction, but regulate myosin-actin binding
Term
Tropomyosin
Definition
A regulatory protein that lies in the groove of F actin and, in relaxed muscle, blocks the myosin-binding active sites
Term
Troponin
Definition
A regulatory protein associated with tropomyosin that acts as a calcium receptor
Term
Titin
Definition
A springy protein that forms the elastic filaments and anchors the thick filaments to the Z discs
Term
Dystrophin
Definition
A large protein that links thin filaments to transmembrane proteins, which, in turn, are linked to extracellular proteins; transfers the force of sarcomere contraction to the fibrous connective tissues of a muscle
Term
Striations
Definition
Alternating light and dark transverse bands across a myofibril
Term
A band
Definition
Dark band formed by parallel thick filaments that partly overlap the thin filaments
Term
H band
Definition
A lighter region in the middle of an A band that contains thick filaments only; thin filaments do not reach this far into the A band in relaxed muscle
Term
M line
Definition
A dark line in the middle of an H band marking the origin of the thick filaments
Term
I band
Definition
A light band composed of thin filaments only
Term
Z disc
Definition
A disc of protein to which thin and elastic filaments are anchored at each end of a sarcomere; appears as a narrow dark line in the middle of the I band, and is often called the Z line
Term
Sarcomere
Definition
A segment from one Z disc to the next; the contractile unit of a muscle fiber
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