Lesson 20 Muscle Tissue A primary tissue type three types of muscle tissue 1 Skeletal muscle tissue voluntary control 2 Cardiac muscle tissue located in the heart involuntary control 3 Smooth muscle tissue located in viscera blood vessels involuntary control Skeletal Muscles Are attached to the skeletal system Allow us to move The muscular system includes only skeletal muscles does not include cardiac muscles not smooth muscles Sic functions 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 Ex sphincters in alimentary canal urethra 5 Maintain body temperature Ex contractions shivering produce heat 6 Store nutrients reserves muscle protein breaks down when nutrients needed Organization of connective tissues Muscles have three layers of connective tissues outermost to innermost Components of skeletal muscle Muscle tissue muscle cells or fibers Connective tissues Nerves Blood vessels o Epimysium o Perimysium o Endomysium Epimysium Exterior dense collagen layer Connected to deep fascia Separates muscle from surrounding tissues Perimysium Endomysium Consists of collagen and elastic fibers Contains blood vessel and nerve supply to fascicles Surrounds muscle fiber bundles fascicles Surrounds individual muscle cells muscle fibers o A muscle cell is also called a muscle fiber Contains capillaries and nerve fibers contracting muscle cells Contains myosatellite cells stem cells that repair damage minimal repair ability Muscle attachments Endomysium perimysium and epimysium come together at ends of muscles to form connective tissue attachment to bone matrix o i e tendon bundle or aponeurosis sheet Blood vessels and nerves Muscles have extensive vascular systems that o Supply large amounts of oxygen o Supply nutrients o Carry away wastes Skeletal muscles are voluntary muscles controlled by nerves of the central nervous system brain and spinal cord o Receive input from motor neurons Characteristics of 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 regulatory protein of tropomyosin also part of thin filaments o Thick filaments made of the protein myosin The sarcoplasmic reticulum 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 Cisternae functions Is formed by one T tubule and two terminal cisternae o Concentrate Ca2 via ion pumps Ca2 pumps use ATP to actively pump Ca2 into the SR from the sarcoplasm o Release Ca2 into sarcomeres to begin muscle contraction occurs when voltage gated Ca2 are stimulated Sarcomeres The contractile units of muscle A striped or striated pattern within myofibrils Form visible patterns within myofibrils o Alternating dark thick filaments A bands and light thin filaments I bands The A Band o M line o H band The center of the A band At midline of sarcomere anchors thick filaments 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 on the F actin strands Troponin o A globular protein o Binds tropomyosin to G actin o 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 the F actin strand Exposes active site of F actin o Active sites are myosin binding sites o Tropomyosin strand shifts its position so it no longer covers the active site of 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 Binds to other myosin molecules o Head Made of two 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 alongside 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 The control of skeletal muscle activity The neuromuscular junction NMJ o Special intercellular connection between the nervous system and skeletal muscle fiber muscle fiber o Neurotransmitter ACh released into synaptic cleft
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