Tissue and Cellular Organization of Muscle Claudia Stanescu Ph D Office Hours in Gittings 108 Tue 10 11am and Thurs 1 2pm or by appointment Objectives 1 List and describe the specific functions of skeletal muscle 2 Diagram and label the major structural and contractile elements of a muscle fiber and describe the function of each element 3 Diagram and label the major contractile and regulatory elements of the sarcomere Muscle Structure and Function Three types of muscle 1 Skeletal Muscle 2 Cardiac Muscle 3 Smooth Muscle Basic function of all three types is the same Generate Tension Functions of skeletal muscle Locomotion Facial expression Posture and body position Regulation of body temperature Structural Organization of Skeletal Muscle Not shown in figure Groups of muscles covered by Deep Fascia Muscle covered by Epimysium Fascicle covered by Perimysium Muscle fiber covered by Endomysium Not the same as the muscle cell membrane Spaghetti analogy Muscle fiber bag of spaghetti Fascicle Costco 6 pack of spaghetti bags Muscle Box of 6 packs Structural Organization of Skeletal Muscle Organ Tissue Cell Subcellular Cellular and Subcellular Skeletal Muscle Structure 1 Muscle cells are called fibers can be very large 100 m in diameter many cm long 2 Typically multinucleate arising from fusion of myoblasts Prior to birth After birth growth of muscle fibers happens by hypertrophy rather than hyperplasia muscle fibers cannot undergo mitosis Satellite cells have the ability to undergo mitosis after birth to aid in muscle regeneration 3 Units of Organization 1 Conduction of electrical signals sarcolemma 2 Control of muscle contraction sarcoplasmic reticulum 3 Contraction myofibrils Conduction 1 Plasma membrane sarcolemma a surrounds cytoplasm sarcoplasm b Transverse tubules T tubules arise from sarcolemma Control 2 Sarcoplasmic Reticulum smooth ER stores calcium a close proximity to T tubules b surrounds myofibrils sarcolemma calcium T tubule calcium SR SR calcium calcium Control Contraction 3 Myofibrils a longitudinal bundles of protein filaments inside the muscle fiber actin myosin b highly organized into repeating units SARCOMERES Spaghetti Analogy Muscle fiber bag of spaghetti Sarcolemma plastic bag Myofibrils spaghetti strands sarcomere sarcomere sarcomere sarcomere I band thin filament Sarcomere A band I band thick filament myosin Sliding Filaments I band A band Shortening I band incl actin thin filament Sarcomere Davidson College Biology 111 Home Page video http www bio davidson edu misc movies musclcp mov actin myosin contractel Structural muscle proteins Titin spans half of each sarcomere from Z disc to M line stabilizes the position of the thick filament gives muscle its elasticity and extensibility actinin found in the Z disc binds to actin molecules of the thin filament and to titin Structural muscle proteins Myomesin Found in the M line m middle of sacromere Binds to titin and thick filaments to connect them together at the M line Dystrophin links thin filament with sarcolemma IMPORTANT Cytoskeletal protein that links the thin filaments to the sarcolemma Attached to the extracellular proteins in the connective tissues surrounding the muscle fibers Helps transmit tension from the sarcomeres to tendons shorten sarcomere shorten muscle actinin myomesin myofibril force produced inside myofibril doesn t get transferred w dystrophin major weakness muscular distrophy