CBIO 2200 1nd Edition Lecture 15 Outline of Last Lecture I The Ribs II The Pelvis Outline of Current Lecture I Structure of a Muscle Fiber Cell II The Skeletal Muscle Fiber III The Myofibril IV Sarcomere V The Nerve Muscle Relationship Current Lecture I II Structure of a Muscle Fiber Cell a Elongated cells b Organization i Muscle Fascicles Muscle fibers cells Miofibrils Thick and thin filaments myofilaments c Mysium i Epimysium around muscle ii Periomysium around fascicles iii Endomysium around individual muscle fibers cells The skeletal muscle fiber a Multiple nuclei b Myoblasts stem cells that fuse to make each muscle fiber c Satellite cells stem cells or undifferentiated myoblasts help repopulate muscle a d Mitochondria e Sarcolemma plasma membrane of muscle f Sarcoplasm cytoplasm of muscle cells g Myofibrils long protein cords that occupy the sarcoplasm h Glycogen storage form of glucose These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute i III IV V Myoglobin muscle form of hemoglobin red pigment that stores oxygen in muscle j Sarcoplasmic reticulum SR ER of muscles goes around all myofibrils k Terminal cisternae dilations of the sarcoplasmic reticulum l Transverse T tubules tubular infoldings which penetrate through the cell and emerge on the other side m Triad composed of the two terminal cisternae and one transverse tubule The Myofibril a Each myofibril is a bundle of parallel protein microfilaments called myofilaments b Thick filament i Myosin shaped like a golf club with two chains intertwined to form a shaft like tail and a double globular head projecting from it at an angle ii Made of several hundred molecules of myosin c Thin filaments i Actin ii Consists of two intertwined strands of fibrous F actin each F actin is like a bead necklace 1 A string of globular G actin makes up F actin contain myosin binding sites iii Contractile proteins do the work iv Regulatory proteins regulate muscle contraction 1 Tropomyosin covers myosin binding sites on actin 2 Troponin lays on top of tropomyosin has calcium binding sites on them when calcium binds the troponin tropomyosin complex roles away and reveals myosin binding sites d Elastic filaments made up of springy protein called titin i Titin aka connectin anchors myosin to Z discs keeps muscles from overstretching Sarcomere a The distance between two z discs i Anisotropic A band contains thick thin and elastic filaments ii H Band in very middle of A band contains thick and elastic filaments iii M line in middle of H band complex of proteins that are there for structural purposes iv I band thin and elastic filaments go from end of A band to the Z disc b Sarcomere shortening i Dystrophin and other linking proteins that transfer information to extracellular tissue ii Many different linking proteins one of most famous is dystrophin iii Duchenne muscular dystrophy dystrophin linking protein is mutated in this disorder The Nerve Muscle Relationship a Skeletal muscle will not contract without nerve signal b Denervation atrophy muscle atrophies when a nerve signal is blocked from the muscle c Somatic motor neurons innervate skeletal muscles each nerve can innervate multiple muscle fibers but each muscle fiber is only innervated by one nerve d Motor unit one nerve fiber and all the muscle fibers innervated by it i Average motor unit nerve innervating 200 muscles ii Large motor units up to 1000 muscle fibers innervated iii Small motor units innervating 5 to 10 muscle fibers for small motor movements e Neuromuscular Junction where nerve meets the muscle i It creates a distinct area ii Synapse neuromuscular junction where a nerve fiber meets any muscle fiber iii Junctional folds in foldings in the sarcolemma that increase surface area of ACh sensitive membranes iv Synaptic knob a bulbous swelling at the end of the nerve fiber v Synaptic cleft space between nerve and muscle pre synaptic membrane nerve membrane post synaptic membrane muscle membrane vi Acetylcholine receptors vii Schwann cell myelin producing cells viii Exocytosis