Tissue and Cellular Organization of Muscle Claudia Stanescu, Ph.D. Office Hours in Gittings 108 Tue 10-11am and Thurs 1-2pm or by appointmentObjectives: 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 TensionFunctions of skeletal muscle • Locomotion • Facial expression • Posture and body position • Regulation of body temperatureStructural Organization of Skeletal Muscle Groups of muscles (covered by) Deep Fascia Muscle (covered by) Epimysium Fascicle (covered by) Perimysium Muscle fiber (covered by) Endomysium Not shown in figure Not the same as the muscle cell membraneSpaghetti analogy • Muscle fiber = bag of spaghetti • Fascicle = Costco 6 pack of spaghetti bags • Muscle = Box of 6 packsStructural Organization of Skeletal Muscle Organ Tissue Cell SubcellularCellular 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’• 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. Prior to birth3 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.SR SR 2. Sarcoplasmic Reticulum (smooth ER) – stores calcium a. close proximity to T-tubules b. surrounds myofibrils sarcolemma T-tubule calcium calcium calcium calcium “Control”“Control”3. Myofibrils a. longitudinal bundles of protein filaments inside the muscle fiber b. highly organized into ‘repeating units’ actin & myosin SARCOMERES “Contraction”Spaghetti Analogy • Muscle fiber = bag of spaghetti • Sarcolemma = plastic bag • Myofibrils = spaghetti strandssarcomere sarcomere sarcomere sarcomereA-b and I-bandI-bandthin filamentthin filamentthick filamentShorteningA-b and I-bandI-bandSliding Filaments incl. actin myosin SarcomereSarcomereDavidson College Biology 111 Home Page http://www.bio.davidson.edu/misc/movies/musclcp.mov (video!)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 α-actinin – found in the Z disc – binds to actin molecules of the thin filament and to titin -actin + myosin = contractelMyomesin – Found in the M line – Binds to titin and thick filaments to connect them together at the M line Dystrophin – 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 Structural muscle proteins (m = middle of sacromere)(links thin filament with sarcolemma)IMPORTANT!!shorten sarcomere = shorten muscleα-actinin myomesin(myofibril)-force produced inside myofibril doesn’t gettransferred w/dystrophin (major weakness)(muscular