28 terms

Skeletal Muscle

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Myofibril
A bundle of sarcomeres. There are multiple of these in each muscle cell.
Sarcolemma
The cell membrane of a muscle cell. It includes a layer of polysaccharides and collagen fibrils.
Myofiber
A single muscle cell that bundles several myofibrils together.
Endomysium
A layer of connective tissue that sheaths muscle fibers, surrounding their sarcolemma. Composed mostly of reticular fibers. Nerves, capillaries and lymphatics run through it.
Fasicle
A bundle of muscle fibers surrounded by perimysium
Perimysium
The layer of connective tissue surrounding a fasicle.
Epimysium
A layer of connective tissue ensheathing an entire muscle. Composed of dense irregular connective tissue.
Z disk
The disk that sarcomeres connect to
Components of Thin Filament
Actin, Troponin, Tropomyosin
Components of Thick Filament
Myosin
Dystrophin
attaches portions of cell membrane to sarcomere; important in contraction. Binds f-actin.
Desmin
Connective protein, binds sarcomeres of adjacent myofibrils together
alpha-actinin
anchors protein that anchors actin myofilaments to Z line
Nebulin
A structural protein that wraps around the entire length of each thin filament; it helps anchor the thin filaments to the Z discs and controls G-actin polymerization
M-line
supporting proteins that hold the thick filaments together in the H zone in a regular array. Also provides ATP from creatinine phosphate.
C-stripes
Hold myosin in regular array.
Titin
protein that connects m line to z line, maintains the position of the myosin in the center of the sarcomere and prevents the sarcomere from being pulled apart (resting tension). Giant protein spring responsible for resting muscle elasticity.
Tropomyosin
A helical protein that winds around actin helices in skeletal and cardiac muscle cells to form the thin filament of the sarcomere. In the absence of Ca2+, it covers the myosin-binding sites on actin and prevents muscle contraction. When calcium is present, a conformation change in tropomyosin occurs so that the myosin-binding sites are exposed and muscle contraction can occur.
Troponin
A globular protein that ssociated with tropomyosin as part of the thin filament of the sarcomere. It binds Ca2+, which causes the conformaiton change in tropomyosin required to expose the myosin-binding sites on actin and initiate muscle contraction.
Actin
A globular protein that links into chains, two of which twist helically about each other, forming microfilaments in muscle and other contractile elements in cells. This makes up the thin filament.
Myosin
Makes up the thick filament. 2 Heavy chains and 4 light chains. 1 HC + 2 LC make a head. Myosin is a doubled headed spiral of 2 HCs. Head has actin binding site and ATPase activity.
A band
Band in sarcomere that covers all of the myosin and partially overlaps the actin.
I band
Band in sarcomere that covers actin but not myosin. Shrinks when muscle contracts.
H band
Band in sarcomere that covers myosin but not actin filaments. Shrinks when muscle contracts.
Triad
2 terminal cisterna of the sarcoplasmic reticulum and 1 transverse tubule. At the junction of the A band and I band.
Golgi Tendon Organ
Located at the musclo-tendon junction, these sensory organs detect excessive muscle contraction. Consists of encapsulated collagen fibers and type Ib sensory nerves.
Muscle Spindles
Intrafusal fibers that sense the length and rate of change of length of extrafusal fibers. They can initiate a stretch reflex to prevent injury.
Satellite Cells
Special motile stem cells that can replace muscle cells to repair muscle injury. Unlike differentiated muscle, they can mitose.