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Muscle Physiology

Muscle Physiology. Chapter 11. Connective Tissue Components. Muscle cell = muscle fiber Endomysium – covers muscle fiber Perimysium – binds groups of muscle fibers ( fasicles ) Epimysium – covers the entire muscle Tendon – fibrous tissue that connects muscle to bone

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Muscle Physiology

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  1. Muscle Physiology Chapter 11

  2. Connective Tissue Components • Muscle cell = muscle fiber • Endomysium – covers muscle fiber • Perimysium – binds groups of muscle fibers (fasicles) • Epimysium – covers the entire muscle • Tendon – fibrous tissue that connects muscle to bone • Aponeurosis – broad, flat sheet of connective tissue • Fascia – fibrous CT surrounding muscle and tendon

  3. Overview of Muscle Cell • Muscle cell = muscle fiber • Sarcolemma = plasma membrane • Sarcoplasm = cytoplasm • Sarcoplasmic reticulum (SR) = network of tubules and sacs • Multi-nucleated, multiple mitochondrion • Bundles of myofibrils extend lengthwise & fill sarcoplasm • Composed of thick and thin myofilaments

  4. Sarcomere • Contractile unit of a muscle fiber • each myofibril consists of many sarcomeres • Z line • Anchors thin filaments • Boundary of sarcomere • M line – anchors thick filaments • A band: segment of thick & thin filaments • I band: segment of thin filaments • H zone: where thin and thick filaments will not overlap (only thick)

  5. Sarcomere cont… • Elastic filaments – connect thick filaments to Z line • T (transverse) tubules – allows impulses traveling along sarcolemma to move deeper within the cell • Triad – t tubule sandwiched between sacs of the SR • Allows impulses traveling along a t tubule to stimulate sacs of the SR

  6. Myofilaments • Myofibrils – made up of 1000s of thin and thick myofilaments • Thin filaments • Actin • Tropomyosin • Troponin • Thick filaments • myosin

  7. Muscle Excitation • Nerve impulse reaches the end of a motor neuron  releases acetylcholine (Ach) • Ach diffuses across the neuromuscular junction and binds with the receptors on the motor endplate

  8. Muscle Contraction • Impulses travel along the sarcolemma  t tubules  sacs of SR • Ca2+ is released (balloons to distract)into the sarcoplasm  binds with troponin(chaperone) • Tropomyosin shift to expose actin’s active site • Energized myosin (Boy) KISSES (bind) with actin’s(girl) active site and pulls (her to middle of the dance floor)thin filament towards center of sarcomere • Requires ATP

  9. Muscle Relaxation • Nerve impulse is complete  Ca2+ is pumped back into the sacs of the SR • Ca2+ is stripped from the troponin  tropomyosin covers the actin’s active site • Myosin heads can no longer bind with actin  muscle fiber returns to its resting length

  10. http://www.sci.sdsu.edu/movies/actin_myosin_gif.html

  11. Rigor Mortis • “stiffness of death” • SR releases excess Ca2+  myosin heads bind with actin’s active sites  contraction of myofilaments • Lack of ATP after death causes cross bridges to “stick”

  12. http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter9/http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter9/

  13. Alternate Source of Energy • ATP must be continually re-synthesized • Breakdown of creatine-phosphate (CP) provides energy for ATP re-synthesis • Catabolism of food provides energy for ATP and CP synthesis

  14. Aerobic vs. Anaerobic Respiration • Aerobic Respiration • Oxygen-requiring process • Produces maximum amount of ATP from one glucose molecule • Anaerobic Respiration • Does not require oxygen • Short-term, rapid process to re-synthesize ATP • Produces lactic acid • Burning/soreness in muscles

  15. Heat Production • Some energy from catabolic processes is lost as heat • Muscle release massive amts of heat • Thermoreceptors sense decrease in body temp  hypothalamus integrates information  signal sent to skeletal muscle to contract  shivering  homeostatic balance is maintained

  16. http://natchem.files.wordpress.com/2009/11/motor-unit-lg.jpg

  17. Isotonic vs Isometric Contractions • Isotonic – tension remains the same; length of the muscle changes • Concentric contraction: muscle shortens (contracts) • Eccentric contraction : muscle lengthens • Isometric – tension changes; length of the muscle remains the same • Myosin heads unable to move thin filaments • Static tension

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