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Understanding Muscle Physiology and Contractions

Explore muscle cell components, sarcomere structure, myofilaments, muscle excitation, contraction, relaxation, and energy sources in muscle physiology. Learn about isotonic and isometric contractions and their impact. Enhance your knowledge of muscle function!

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Understanding Muscle Physiology and Contractions

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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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