Lesson 20 The Muscular System 12 06 2015 An introduction to muscle tissue Three types of muscle tissue o Skeletal muscle tissue voluntary control o Cardiac muscle tissue involuntary control Located in the heart o Smooth muscle tissue involuntary control Located in viscera blood vessels 10 1 Functions of skeletal muscle tissue Skeletal Muscles Are attached to the skeletal system Allow us to move The muscular system includes only skeletal muscles does NOT include cardiac muscles or smooth muscles Six functions of skeletal muscle tissue Produce skeletal movement voluntary control Maintain posture and body position Support soft tissues line abdominal wall and pelvic cavity Guard entrances and exits o EX sphincters in alimentary canal urethra Maintain body temperature o EX contractions shivering produce heat Store nutrients reserves o Muscle protein breaks down when nutrients needed 10 2 Organization of Muscle Components of skeletal muscle Muscle tissue muscle cells or fibers Connective tissues Nerves Blood vessels Organization of connective tissues Muscles have 3 layers of connective tissues outermost to innermost o Epimysium o Perimysium o Endomysium Epimysium o Exterior dense collagen layer o Connected to deep fascia o Separates muscle from surrounding tissues Perimysium o Consists of collagen and elastic fibers o Surrounds muscle fiber bundles fascicles o Contains blood vessel and nerve supply to fascicles Endomysium o Surrounds individual muscle cells muscle fibers A muscle cell is also called a muscle fiber o Contains capillaries and nerve fibers contracting muscle cells o Contains myosatellite cells stem cells that repair damage Minimal repair ability Muscle attachments o Endomysium perimysium and epimysium come together at the ends of muscles to form connective tissue attachment to bone matrix i e tendon bundle or aponeurosis sheet Blood vessels and nerves o Muscles have extensive vascular systems that Supply large amounts of oxygen Supply nutrients Carry away wastes o Skeletal muscles are voluntary muscles controlled by nerves of the CNS brain and spinal cord Receive input from motor neurons 10 3 Characteristics of Skeletal Muscle Fibers Skeletal muscle cells Develop through fusion of mesodermal cells myoblasts Become very large up to 100 micrometer diameter Contains hundreds of nuclei o Fusion of myoblasts does not destroy its nucleus are very long up to 12 inches long The sarcolemma and transverse tubules The sarcolemma the cell membrane of a muscle fiber cell o Surrounds the sarcoplasm cytoplasm of muscle fiber o A change in transmembrane potential begins contractions Transverse tubules T tubules o Transmit action potential through cell o Allow entire muscle fiber to contract simultaneously o Have same properties as sarcolemma 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 Actin is regulatory protein of tropomyosin also part of thin filaments o Thick filaments made up of protein myosin The sarcoplasmic reticulum SR A membranous structure surrounding each myofibril Similar in structure to smooth ER 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 Sarcomeres The contractile units of muscle Form visible patterns within myofibrils A striped or straight pattern within myofibrils o Alternating dark thick filaments A bands and light thin filaments I bands The A Band o M Line The center of the A band At midline of sarcomere anchors thick filaments o H Band The area around the M line Has thick filaments but not thin filaments o Zone of Overlap The densest darkest area on a light micrograph Where thick and thin filaments overlap A band minus H band The 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 Thin Filaments F actin filamentous actin o Is two twisted rows of globular G actin o The active sites on G actin strands bind to myosin Nebulin o Protein strand running along the length of the F actin strands o Holds F actin strands together Tropomyosin o Is a double strand o Prevents actin myosin interaction At rest the position of tropomyosin blocks the myosin binding sites found of the F actin strands o Troponin A globular protein Binds tropomyosin to G actin Controlled by Ca2 Binding of Ca2 causes a change in troponin conformation exposes myosin binding sites on F actin strands Initiating contraction Ca2 binds to receptor on troponin molecule Troponin tropomyosin complex changes o Tropomyosin strand shifts its position so it no longer covers the active site of the F actin strand Exposes active site of F actin o Active sites are myosin binding sites Thick filaments Contain about 300 twisted myosin subunits Contain titin strands that recoil after stretching o Helps keep thick and thin filaments aligned and restores resting sarcomere length once muscle relaxes when contraction is over The myosin molecule consists of o Tail o Head Binds to other myosin molecules Made of 2 globular protein subunits Reaches the nearest thin filament can extend and bind to myosin binding site of the nearest thin filament Myosin action During contraction myosin heads o Interact with actin filaments forming cross bridges Requires myosin binding sites on F actin strands to be unblocked by the regulatory filament tropomyosin o Pivot producing motion Sliding filaments and muscle contraction Sliding filament theory o Thin filaments of sarcomere slide toward M line along side thick filaments o The width of A zone band stays the same The width of the H band and I band shrinks during contraction o Z lines move closer together sarcomere length shortens Skeletal muscle contraction The process of contraction o Neural stimulation of sarcolemma Causes excitation contraction coupling o Muscle fiber contraction Interaction of thick and thin filaments o Tension produced 10 4 Components of the Neuromuscular Junction The control of skeletal muscle activity The neuromuscular junction NMJ o Special
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