Final Exam Study Guide (Non-Cumulative Portion)Lesson 20:1. What are the six functions of skeletal muscle tissue?a. Produce skeletal movement (Voluntary)b. Maintain posture and body positionc. Support soft tissues (line abdominal wall and pelvic cavity)d. Guard entrances and exits (ex. Sphincters in alimentary canal, urethra)e. Maintain body temperature (ex. Contractions produce heat (shivering))f. Store nutrient reserves (breaks down muscle protein when needed) 2. How are skeletal muscles organized? What are connective tissue layers that are found covering muscles? What can be found in each layer (blood vessels/nerves)?• Organizationo Muscle tissue (muscle cells or fibers) A muscle cell is also referred to as a muscle fibero Associated with the tissue are: Connective tissues Nerves Blood vessels• Layerso Epimysium - Exterior collagen layer; connected to deep fascia; separates muscle from surrounding tissues.o Perimysium- Surrounds muscle fiber bundles (forms fascicles); Contains blood vessel and nerve supply to fascicleso Endomysium- Surrounds individual muscle cells (muscle fibers); Contains capillaries and nerve fibers contacting muscle cells; Contains myosatellite cells (stem cells) that can repair some damage- minimal repair ability 3. What are the structural components of a muscle fiber? What are myofibrils? What are myofilaments? Structural Components of muscle fibero The Sarcolemma - The cell membrane of a muscle fiber (cell) Surrounds the sarcoplasm (cytoplasm of muscle fiber) A change in transmembrane potential begins contractionso Transverse tubules (T tubules)- invagination of the sarcolemma Have same properties as sarcolemma Transmit action potential through cell Allow entire muscle fiber to contract simultaneouslyo Myofibrils Lengthwise subdivisions within muscle fiber Made up of bundles of protein filaments (myofilaments)• Myofilaments are responsible for muscle contraction • Types of myofilaments:o Thin filaments Made of the protein actin o Thick filaments Made of the protein myosino The Sarcoplasmic Reticulum (SR) Similar in structure to smooth endoplasmic reticulum A membranous structure surrounding each myofibril Forms chambers (terminal cisternae) attached to T tubules Helps transmit action potential to myofibril Triad• Is formed by one T tubule and two terminal cisternae • Cisternae functions to:o Concentrate Ca2+ (via ion pumps)- Ca2+ pumps use ATP to actively pump Ca2+ into the SR from the sarcoplasm o When stimulated by an action potential, the cisternae release Ca2+ into sarcomeres to begin muscle contraction 4. What are the differences between thick and thin filaments? How are they organized in muscle fibers? How are they arranged in a sarcomere? Myofilaments: Protein filaments responsible for muscle contractiono Thick filaments Made of the protein myosin Contain about 300 twisted myosin subunits Contain titin strands that recoil after stretching Helps keep thick and thin filaments aligned and restores resting sarcomere length after contration The myosin molecule consists of:• Tail - Binds to other myosin molecules • Head - Made of two globular protein subunits Can extend and bind to myosin binding site of the nearest thin filamento Thin Filaments Made of the protein actin F-actin (filamentous actin) - Two twisted rows of globular G-actin • The active sites on G-actin strands bind to myosin Tropomyosin - double strand regulatory protein• Prevents actin–myosin interaction Troponin - A globular regulatory protein• Binds tropomyosin to G-actin • Controlled by Ca2+ - Binding of Ca2+ causes a change in troponin o Arrangement in Sarcomere The A Band• M line - The center of the A band• At midline of sarcomere The H band - The area around the M line• Has thick filaments but no thin filaments Zone of overlap - The densest, darkest area on a light micrograph • Where thick and thin filaments overlap The I Band• Z lines - The centers of the I bands• At two ends of sarcomere Titin - Are strands of protein • Reach from tips of thick filaments to the Z line• Stabilize the filaments5. What are the zones and lines in a myofibril? What are the different regulatory and structural proteins found in a muscle fiber? What are their functions? Lines and Zoneso The A Band M line - The center of the A band At midline of sarcomere o The H band - The area around the M line Has thick filaments but no thin filamentso Zone of overlap - The densest, darkest area on a light micrograph Where thick and thin filaments overlap o The I Band Z lines - The centers of the I bands• At two ends of sarcomere Titin - Are strands of protein • Reach from tips of thick filaments to the Z line• Stabilize the filaments Regulatory and structural Proteins in muscle fibero F-actin (filamentous actin) - Two twisted rows of globular G-actin The active sites on G-actin strands bind to myosino Tropomyosin - double strand regulatory protein Prevents actin–myosin interaction o Troponin - A globular regulatory protein Binds tropomyosin to G-actin Controlled by Ca2+ - Binding of Ca2+ causes a change in troponin 6. How are T tubules related to the sarcolemma? Why are they important to a muscle fiber? What is a triad and why is it important?• Transverse tubules (T tubules)- invagination of the sarcolemma o Have same properties as sarcolemma o Transmit action potential through cello Allow entire muscle fiber to contract simultaneously• Triad- formed by one T tubule and two terminal cisternaeo Cisternae functions to: Concentrate Ca2+ (via ion pumps)- Ca2+ pumps use ATP to actively pump Ca2+ into the Sarcoplasmic reticulum from the sarcoplasm When stimulated by an action potential, the cisternae release Ca2+ into sarcomeres to begin muscle contraction 7. What is the function of calcium in muscle contraction? Where is it normally concentrated in a muscle fiber? How is it concentrated there?• During the initiation of a contractiono Ca2+ binds to receptor on troponin moleculeo Troponin–tropomyosin complex changeso Tropomyosin strand shifts in position so it no longer covers the active site of the F-actin strando Exposes active site of actin• Calcium concentrationo Terminal Cisternae Concentrate Ca2+ (via ion pumps)- Ca2+ pumps use ATP to actively pump Ca2+ into the SR
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