Clicker questions • Clicker channel: 70 • Response Ware session ID: psio201For a person sitting normally in a chair, with feet flat on the floor, which of the following statements is correct? A. thigh and leg are extended. B. thigh and leg are flexed. C. thigh is extended, leg is flexed. D. thigh is flexed, leg is extended. A. B. C. D.0%1%0%99%For a second class lever, which of the following statements is correct? A. the effort is between the fulcrum and the load. B. the fulcrum is between the load and the effort. C. the load is between the effort and the fulcrum. A. B. C.91%7%2%Lecture 17: Tissue and Cellular Organization of Muscle Office hours: Tuesday and Thursday 1-2pm in Gittings 108 or by appointment Claudia Stanescu, Ph.D.Objectives (pp. 291-301, sec. 10.1-10.2): 1. Describe the organization of muscle and the connective tissues surrounding each structure. 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. 4. Diagram and label the thin and thick filaments including all of the proteins that make up each myofilament. 5. Give a general description of the sliding filament mechanismStructural 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 membraneStructural Organization of Skeletal Muscle Organ Tissue Cell SubcellularCellular and Subcellular Skeletal Muscle Structure 1. Muscle cells are called ‘fibers’ can be very large (100 mm 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 birth increase in size increase in number Muscle development3 Functional Units of Organization 1) Conduction of electrical signals • sarcolemma 2) Control of muscle contraction • sarcoplasmic reticulum 3) Contraction • myofibrils inside muscle fibers“Conduction” 1. Plasma membrane (sarcolemma) a. surrounds cytoplasm 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”Clicker questions • Clicker channel: 70 • Response Ware Session ID: psio201Which of the following is true about the connective tissue covering of muscle? A. Endomysium covers the muscle fascicle. B. Perimysium covers the myofibrils. C. Epimysium covers the muscle fiber. D. Deep fascia covers a group of muscles. A. B. C. D.8%63%24%5%Which skeletal muscle structure stores calcium? A. Sarcolemma B. Mitochondria C. Sarcoplasmic reticulum D. Myofibrils E. Transverse-tubules A. B. C. D. E.2%1%1%97%0%Which skeletal muscle structure contracts and generates force? A. Sarcolemma B. Mitochondria C. Sarcoplasmic reticulum D. Myofibrils E. Transverse-tubules A. B. C. D. E.4%2%92%2%0%Sarcomeressarcomere sarcomere sarcomere sarcomereA-band I-bandI-bandthin filamentthin filamentthick filamentShorteningA-band I-bandI-bandSliding Filaments incl. actin myosin SarcomereSarcomereMuscle proteins 1) Contractile proteins – Actin and myosin 2) Regulatory proteins – Troponin and tropomyosin 3) Structural proteins – Titin, dystrophin, α-actinin, myomesin, nebulinContractile Proteins 1) Actin • found in thin filaments • has myosin binding sites for crossbridge formation with myosin 2) Myosin • motor protein found in thick filaments • has myosin head that binds to the myosin binding site on actin and forms crossbridge during muscle contractionSarcomeres: Functional Unit of Contraction Elements of Sarcomere Structure 1. Thin Filament Attached to Z line (Z disc) Z ‘myosin binding site’ on actin covered by regulatory proteins: troponin and tropomyosin composed of two helically arranged strands of actin two twisted strands of pearlsRegulatory Proteins 1) Tropomyosin • found in thin filaments • covers the myosin binding sites on actin when muscle is relaxed 2) Troponin • found in thin filaments • holds tropomyosin in place when muscle is relaxed • during contraction, calcium binds to troponin and causes a conformational change that shifts tropomyosin away from the myosin binding sites on actin  exposes the binding sites to allow crossbridge formationSarcomeres: Functional Unit of Contraction Elements of Sarcomere Structure 2. Thick Filament ‘myosin head’ has ATPase activity when bound to actin imagine two golf clubs with their handles twisted about each other spans the distance and overlaps thin filaments Z composed of a highly organized array of myosin moleculesStructural 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; and helps the sarcomere return to resting length after contraction 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 tendonsNebulin – spans the length of the thin filament – anchors thin filaments to Z disc α-actinin – found in the Z disc – binds to actin molecules of the thin filament and to titin Myomesin – Found in the M line – Binds to titin and thick filaments to connect them together at the M line Structural muscle proteinsα-actinin myomesinDystrophinNebulin http://droualb.faculty.mjc.edu/Lecture%20Notes/Unit%203/chapter_9__skeletal_muscle_tiss%20with%20figures.htmSliding Filament Model of Muscle Contraction 1. Myosin ‘heads’ bind to actin to form a ‘crossbridge’ 2. Conformational change, energized by ATP hydrolysis, causes thin filaments to slide along thick filaments 3. Myosin head groups release, form new crossbridges, and the sliding cycle repeats...