Exam 5 Learning Objectives Lesson 20 The Muscular System Describe the three types of muscle tissue o Skeletal muscle tissue o Cardiac muscle tissue o Smooth muscle tissue voluntary control located in the heart involuntary control located in viscera blood vessels involuntary control Explain the function of skeletal muscle tissue 1 Produce skeletal movement voluntary control 2 Maintain posture and body position 3 Support soft tissues line abdominal wall and pelvic cavity 4 Guard entrances and exits sphincters in alimentary canal urethra 5 Maintain body temperature contractions shivering produce heat 6 Store nutrients reserves muscle protein breaks down when nutrients needed Describe the connective tissue that covers skeletal muscles o Epimysium o Perimysium Exterior dense collagen layer Connected to deep fascia Separates muscle from surrounding tissues Consists of collagen and elastic fibers Surrounds muscle fiber bundles fascicles Contains blood vessel and nerve supply to fascicles o Endomysium Surrounds individual muscle cells muscle fibers A muscle cell is also called a muscle fiber Contains capillaries and nerve fibers contacting muscle cells Contains myosatellite cells stem cells that repair damage minimal repair ability o How do they form tendons aponeuroses Endomysium perimysium and epimysium come together at ends of muscles to form connective tissue attachment to bone matrix tendon bundle or aponeurosis sheet Describe the characteristics of skeletal muscle cells o Develop through fusion of mesodermal cells myoblasts o Become very large up to 100 micrometer diameter o Contain hundreds of nuclei Fusion of myoblasts does not destroy its nucleus o Are very long up to 12 inches long o Why do they have multiple nuclei What are the function of the sarcoplasmic reticulum and transverse tubule The sarcolemma The cell membrane of a muscle fiber cell Surrounds the sarcoplasm cytoplasm of muscle fiber A change in transmembrane potential begins contractions Transverse tubules T tubules Transmit action potential through cell Allow entire muscle fiber to contract simultaneously Have same properties as sarcolemma Sarcoplasmic Reticulum SR A membranous structure surrounding each myofibril Similar in structure to smooth endoplasmic reticulum Forms chambers terminal cisternae attached to T tubules Helps transmit action potential to myofibril Triad o Is formed by one T tubule and two terminal cisternae o Cisternae functions Concentrate Ca2 via ion pumps Ca2 pumps use ATP to actively pump Ca2 into the SR from the sarcoplasm Release Ca2 into sarcomeres to begin muscle contraction occurs when voltage gated Ca2 are stimulated Describe the arrangement of the sarcomere o Sarcomeres the contractile units of muscle Structural units of myofibrils Form visible patterns within myofibrils A striped or striated pattern within myofibrils Explain how the myofilaments are arranged in the sarcomere o Alternating dark thick filaments A bands and light thin filaments I bands o What are the different regions A band I band etc of the sarcomere and which myofilament is found there A band M line o The center of the A band o At midline of sarcomere anchors thick filaments o The area around the M line o Has thick filaments but no thin filaments o The densest darkest area on a light micrograph o Where thick and thin filaments overlap A band minus H band H band Zone of overlap I band o Z lines The centers of the I bands At two ends of sarcomere o Titin Are strands of protein Reach from tips of thick filaments to the Z line Stabilize the filaments Describe the components of the thin and thick filaments o Thin filaments F actin filamentous actin Is two twisted rows of globular G actin The active sites on G actin strands bind to myosin Protein strand running along the length of the F actin strands Holds F actin strands together Nebulin Tropomyosin Is a double strand Prevents actin myosin interaction on the F actin strands Troponin o At rest the position of tropomyosin blocks the myosin binding sites found A globular protein Binds tropomyosin to G actin Controlled by Ca2 binding of Ca2 causes a change in troponin conformation Helps keep thick and thin filaments aligned and restores resting sarcomere length o Reaches the nearest thin filament can extend and bind to myosin binding exposes myosin binding sites on F actin strands o Thick filaments Contain about 300 twisted myosin subunits Contain titin strands that recoil after stretching once muscle relaxes when contraction is over The myosin molecule consists of Tail binds to other myosin molecules Head made of two globular protein subunits site of the nearest thin filament o What is the function of these components Initiating contraction Ca2 binds to receptor on troponin molecule Troponin tropomyosin complex changes of the F actin strand Exposes active site of F actin o Active sites are myosin binding sites Explain how the thick and thin filaments interact o Myosin action o Tropomyosin strand shifts its position so it no longer covers the active site During contraction myosin heads interact with actin filaments forming cross bridges Requires myosin binding sites on F actin strands to be unblocked by the regulatory filament tropomyosin Pivot producing motion o What is the sliding filament theory Thin filaments of sarcomere slide toward M line alongside thick filaments The width of A zone band stays the same The width of the H band and I band shrinks during contraction Z line move closer together sarcomere length shortens Describe the neuromuscular junction and excitation contraction coupling o Neuromuscular Junction Special intercellular connection between the nervous system and skeletal muscle fiber Neurotransmitter Ach released into synaptic cleft causes action potential in muscle fiber Muscle fiber responds by releasing calcium ion into the sarcoplasm calcium stored in the sarcoplasmic reticulum is released o Excitation Contraction Coupling Action potential reaches a triad Releases Ca2 from sarcoplasmic reticulum triggering contraction Requires myosin heads to be in cocked position loaded by ATP energy Lesson 21 Muscle Contraction Describe the events that occur at the neuromuscular junction during the generation of an action potential at the sarcolemma o 1 The cytoplasm of the axon terminal contains vesicles filled with molecules of acetylcholine or Ach Acetylcholine is a neurotransmitter a chemical released by a neuron to change the permeability or other properties of
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