Skeletal muscle structureSkeletal muscles are connected to at least 2 bonesoEXCEPT that some are connected to the skin, to cartilage, or to other muscles.Tendons- elastic connective tissue that connects muscles to bonesStructure at the cellular levelThe body of the muscle generates force.Epimysium- connective tissue surrounding the body of the musclePerimysium is under the epimysium and is divided into fasciclesFascicles are made up of thousands of muscle fibers (cells)Muscle fibers run the whole length of the muscle and is encased in the endomysium. Muscle fibers have many nuclei’s.Sarcolemma- muscle fibers plasma membrane, nucleus’s lie right underneathSarcoplasm- muscle fibers cytoplasm, packed w/ mitochondria, and myofibrils Myofibrils- fibers contractile machinery oMade of:Myosin thick filamentsActin thin filamentSarcoplasmic reticulum-surrounds each myofibril & is associated with T tubulesoNear the T- tubules the sarcoplasmic reticulum has terminal cisternae which store calcium.T tubules- continuous with sarcolemma and penetrate inside the cell.oEach t tubule has 2 lateral sacs called TRIADThe SR and T-tubules are important in muscle contractionsoThey transmit signals from the sarcolemma to myofibrils- enabling a muscle cell to respond to a stimulus. The calcium from the SR is released and travels to sarcolemma to BoneTendonMuscle bodyPerimysiumEpimysiumFascicleMuscle fiber (cell)MyofibrilSarcolemmaProtein filamentsMuscle fibers in fascicleEndomysiumNucleus
the t-tubules, serving as a messenger & carries signals to myofibrils to initiate contraction.Structure at the molecular levelStriated muscle- striped appearanceoStriped are due to thick and thin filaments, 2:1 ratioMyofibrils are composed of sarcomeresoSarcomeres are bordered on either end by the Z lines. Z lines anchor thin filaments at one end.oM lines- connect thick filaments A-band: thick filaments.H zone- the center of the A band where it is lighter than the sides b/e only thick filaments are present and thin filaments are not overlapping.I band- thin filaments with no overlap of thick filamentsoThe center of the I band is where the Z line connects the thin filamentsContractile proteins make up thick and thin filaments- myosin and actin b/e they generate the contractile force
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- Fall '08