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Sliding Filament Theory of Muscle Contraction4.2 .5 Rigor Mortis Models February 22, 2016

• Structure of a Muscle Cello Muscle Cell, or fiber

Single cellSurrounded by endomysium (connective tissue)

o FascicleSurrounded by perimysium

o Skeletal MuscleGroup of fasciclesSurrounded by epimysium

• Muscle Cellso Each fiber is a single cell

Multiple nucleiBundle of myofibrils (long organelles)

• Thin filaments• Thick filaments

Surrounded by sarcolemma• Specialized plasma membrane

Sarcoplasmic reticulum• Specialized endoplasmic reticulum• Stores calcium ions

o Vitamin D helps with Calcium Uptake

Made of individual units called sarcomeres .• Basic contractile unit of the muscle

Thick Filaments• Myosin• Cross-bridge

Thin Filaments• Actin

• The Sliding Filament Theoryo The thick and thin filaments slide past each other longitudinally,

producing more overall between thick and thin filamentso The sarcomere shortens, but the filaments do not change in length.o Based on the interaction between actin and myosin molecules.

o At rest, myosin binding sits on the thin filament (actin) are blockedby tropomyosin

For the muscle fiber to contract, those binding sits must be

uncoveredOccurs when calcium ions bind to troponin complexControls the position of tropomyosin on the thin filamentCa binding rearranges the tropomyosin-troponin complex toexpose the myosin binding site

o The cross-bridge is broken when a new molecule of ATP binds to myosinhead.

Calcium is signaled to attach to the troponin. This causes the troponin to ,allowing the Actin to bind to Myosin.

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Action potential tells the vesicles to release stuff and receptors(sarcoplasmic reticulum)