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Terms in this set (70)

-Somatic motor neuron releases ACh at neuromuscular junction
-Net entry of Na+ through ACh receptor-channel initiates a muscle AP
-AP in T-tubule alters conformation of DHP receptor
-DHP receptor opens RyR Ca2+ release channels in sarcoplasmic reticulum, and Ca2+ enters cytoplasm
-Ca2+ binds to troponin, allowing actin-myosin binding
-Myosin heads executer power stroke
-Actin filament slides toward center of sarcomere
-Sarcoplasmic Ca2+ATPase pumps Ca2+ back into SR
-Decrease in free cytosolic Ca2+ causes Ca2+ to unbind from troponin
-Tropomyosin re-covers binding site. When myosin heads release, elastic elements pull filaments back to their relaxed position

sarcolemma: This is the plasma membrane

transverse tubules: They are extensions of the cell membrane (sarcolemma) that associate with the ends (terminal cisternae) of the sarcoplasmic reticulum- go around myofibrils
T-tubule brings action potentials into interior of muscle fiber
Without these, a slower and less direct process would occur that would delay the response time of the muscle fiber b/c the AP reach the center of the fiber only by conduction of the AP through the cytosol

SR: Stores Ca2+
This Ca2+ binds to troponin and eventually releases from it

Thin Filaments: Each actin molecule has a myosin cross-bridge binding site
Thin filaments are entwined with tropomyosin molecules which block the cross-bridge binding sites (actin chain)
A three subunit troponin protein complex (TnC, TnT, TnI) is associated with each tropomyosin
One of the troponin subunits (TnC) has a calcium binding site
Each thin filament is surrounded by three thick filaments

Thick filaments: Each one is arranged so that the myosin heads are clustered at Z disk of the filament and the central region of the filament is a bundle of myosin tails
about 250 myosin molecules join to create thick filament
Arranged so that the myosin heads are clustered at each end of the filament, and the center region of the filament is a bundle of myosin tails
Each thick filament is surrounded by 6 thin filaments

Troponin: Binds with Ca2+ in order to move tropomyosin out of the way for myosin to bind to actin and produce the power stroke

Tropomyosin: A tube-shaped protein found in thin actin filaments of muscle fibres. Tropomyosin has a control function; when calcium ion concentration is low within a muscle fibre, the tropomyosin inhibits muscle contraction by blocking the binding site on actin, thereby preventing myosin cross-bridges from attaching