Skeletal muscle fibers
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1. Muscle Physiology 2. Muscle Tissue Review – ______________________________________________ http://www.siumed.edu/~dking2/ssb/NM016b.htm ______________________________________________ 3. Muscle Tissue Characteristics Excitability or Irritability - ______________________________________________ ______________________________________________ ______________________________________________ Contractility - ______________________________________________ Extensibility - ______________________________________________ Elasticity 4. Muscle Key Words Muscle Type Associated Terms General Myo-, Mys-, Sarco-, Fibers Skeletal Striated, Voluntary Cardiac Striated, Involuntary Smooth Visceral, Nonstriated, Involuntary 5. Muscle Functions Production of Movement Locomotion, manipulation Movement of fluids through hollow organs Maintenance of Posture Skeletal muscle Stabilization of Joints Skeletal muscle Generation of Heat Skeletal muscle, body temperature homeostasis 6. Skeletal Muscle – The Organ Skeletal muscle fibers Nerve fibers Nerve fiber for each muscle fiber Blood vessels Highly metabolic Connective tissue 7. Muscle Anatomy Epimysium Dense irregular CT Continuous with other sheaths and with tendons Fascicle - Bundle of muscle fibers Perimysium -Fibrous CT covering of fascicle http://upload.wikimedia.org/wikipedia/commons/8/89/Illu_muscl e_structure.jpg 8.Muscle Fiber Elongated, striated, multinucleate Endomysium Fine sheath CT with reticular fibers http://upload.wikimedia.org/wikipedia/commons/8/89/Illu_muscl e_structure.jpg 9. Series Elastic Components Continuous with each other and with tendon Transmit forces to bone Entry/exit routes Elasticity ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ _____________________________________________ 10. Skeletal Muscle Fiber Sarcolemma Plasma membrane Sarcoplasm Cytoplasm Glycosomes Myoglobin Myofibrils Sarcoplasmic reticulum ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ 11. Myofibrils Parallel rods Bulk of cell volume Striations Features Z disc H zone I band A band M line ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ 12 -13. Sarcomere Segment of myofibril Between adjacent Z discs Functional unit of contractility ______________________________________________ ______________________________________________ http://www.octc.kctcs.edu/gcaplan/anat/images/Image286.gif 14. Anatomy of a Muscle Sarcomeres end-to-end Myofibrils Fibers (endomysium) Fascicles (perimysium) (epimysium) Fascicle ______________________________________________ Myofibril Fiber ______________________________________________ Muscle ______________________________________________ 15. Filaments of Sarcomere Thick filaments A band Thin filaments I band A band except H zone http://www.octc.kctcs.edu/gcaplan/anat/images/Image286.gif 16 -17. Thick Filaments Myosin Two polypetide chains forming tail and 2 heads form cross bridges with thin filaments Central area Tails of myosin Surface Studded with heads Actin binding sites ATP binding sites and enzymes for splitting ATP http://www.ivy-rose.co.uk/Topics/Muscles/Filament.jpg 18. Thin Filaments Actin Two chains Binding site for myosin head Troponin complex – regulatory protein Tropomyosin – block active sites ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ 19- 20. Filaments Thick and thin filaments interdigitate Slide during contraction http://www.snv.jussieu.fr/vie/dossiers/muscles/muscles.htm 21. Sarcomere – Unit of Contraction Filaments Z disc A band I band H zone M line 22. Sliding Filament Theory Contraction of the sarcomere occurs when the actin filaments slide past the myosin filaments http://physioweb.med.uvm.edu/muscle_physio/muscle_contraction/m scl_cntrct_filaments.htm ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ 23 - 26. Contraction H zone disappears I bands get smaller Z discs get closer together A band does not change in length ______________________________________________ 27 - 28. Role of Calcium Low intracellular Ca2+ Relaxation High intracellular Ca2+ Contraction Calcium-troponin binding Tropomyosin unblocks active sites on actin Myosin heads attach to active sites, pulling thin filaments toward center of sarcomere ______________________________________________ 29. http://www.sci.sdsu.edu/movies/actin_myosin_gif.html ______________________________________________ 30. Sarcoplasmic Reticulum Smooth ER Surrounds myofibril Longitudinal Lateral sacs (terminal cisternae) Calcium regulation Storage Release http://www.etsu.edu/cpah/hsci/forsman/Histology%20of%20mu sclefor%20web_files/image009.jpg 31. T Tubules/Transverse Tubules Sarcolemma Continuous w/extracellular space Form triad Terminal cisterna T tubule Terminal cisterna Electrical impulse conduction http://people.eku.edu/ritchisong/musclecell.jpg 32. Triad Electrical impulses conducted via T tubules Triggers calcium release from terminal cisternae ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ _____________________________________________ 33. Innervation Every muscle has a nerve that innervates it Every muscle fiber has nerve fiber that innervates it http://academic.wsc.edu/faculty/jatodd1/351/motor_unit.jpg 34 - 35. Neuromuscular Junction Nerve impulse end of axon at synapse Ca2+ channels open Synaptic vesicles release acetylcholine ACh binds to receptors on muscle fiber ACh receptors have ion channels that open when ACh binds Diffusion of Na+ into muscle fiber, K+ out Depolarization 36. Depolarization of the Sarcolemma Influx of Na+ change in membrane potential Depolarization adjacent areas of sarcolemma Propagation of action potential After depolarization, Na+ channels close, K+ channels open Initial polarized state is restored Refractory period 37. Excitation-Contraction Coupling 38.http://www.blackwellpublishing.com/matthews/nmj.html http://www.blackwellpublishing.com/matthews/myosin.html 39 - 40. Muscle Contraction http://www.cannock.ac.uk/sports/sport_zip/muskel5.html ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ Tension - ______________________________________________ Load – ______________________________________________ http://www.sciencebase.com/images/muscle_contraction.jpg 41. Isotonic Contraction Tension overcomes load Muscle shortens Object moves Measure amount of shortening ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ 42. Isometric Contraction Muscle tension develops Load is not moved Muscle does not shorten Measure muscle tension ______________________________________________ 43. http://img.tfd.com/dorland/thumbs/contraction_isometric.jpg ______________________________________________ 44. Muscle Contraction ______________________________________________ 45. Motor Unit Motor neuron Nerve cell that carries information re: movement Axon branches; Its terminals form multiple neuromuscular junctions with individual muscle fibers ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ Muscle fibers served by that neuron http://fig.cox.miami.edu/~cmallery/150/neuro/c49x38motorunit.jpg 46 - 48. Muscle Twitch Response of a motor unit to an action potential of its motor neuron Phases Latent Contraction Relaxation 49. Latent Phase ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ 50. Contraction Phase ______________________________________________ 51. Relaxation Phase ______________________________________________ 52. Graded Muscle Responses Variations in strength of muscle contractions Grading Frequency of stimulation Changing strength of stimulation 53. Treppe Staircase effect Initial contractions not as strong as those that follow ? - Increasing Ca2+ Active sites on actin Heat leading to pliability and enzyme efficiency 54. Changes in Stimulation - Frequency Wave (or Temporal) Summation If 2 stimuli of same intensity in rapid succession, second twitch stronger that first http://www.abcbodybuilding.com/magazine03/tetanus2.jpg 55. Incomplete Tetanus Increased rate of stimulation leads to sustained but not smooth contract Relaxation time becoming shorter http://www.abcbodybuilding.com/magazine03/tetanus2.jpg 56. Tetanus No relaxation Smooth, sustained contraction 57. http://media.wiley.com/Lux/05/21805.nfg002.jpg 58 - 60. Fatigue Muscle cannot perform at required level Physiologic inability to contract Gradual reduction in performance Muscle is no longer able to sustain its level of tension and begins to elongate Buildup of lactic acid Depletion of glycogen Able to respond to stimulation after rest and adequate blood supply Neuromuscular fatigue 61. Changes in Stimulation - Strength Threshold stimulus ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ First observable contraction occurs Maximal stimulus Strongest stimulus that produces an increase in tension ______________________________________________ 62 - 64. Recruitment Multiple Motor Unit Summation Increasing stimulus increases the number of motor units stimulated Laboratory Increase voltage In Vivo Stimulate more motor neurons Motor units Usually asynchronous Delay fatigue Synchronous Strong contraction ______________________________________________ 65. Summary Multiple Motor Unit Summation Strength of stimulation Increases force of contraction by stimulation of the appropriate number of motor units Wave or Temporal Summation Frequency of stimulation Smoothes contraction via rapid stimulation of muscle cells ______________________________________________ 66. Muscle Tone Continual slight contraction Spinal reflexes Stabilize joints Maintain posture ______________________________________________ 67 - 68. Isotonic Contractions Muscle length changes Load moves ______________________________________________ http://www.octc.kctcs.edu/gcaplan/anat/Notes/API%20Notes% 20J%20Complete%20Muscle%20Contraction.htm Tension increases until sufficient to move load Tension then remains constant through rest of contraction 69 - 70. Isometric Contractions Muscles neither shortens or lengthens Load is greater than force generated by muscle Peak tension developed and maintained but no change in resting length Stabilization of joints Maintenance of posture 71. Comparison Isometric Cross bridges generate force, thin filaments not sliding Isotonic Sliding of thin filaments Both involve same electrochemical and mechanical events ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ _____________________________________________ Most movements of body are combination of both types of contractions ______________________________________________ ______________________________________________ 72. Force of Muscle Contraction Number of fibers stimulated Multiple Motor Unit Summation Frequency of stimulation Wave or Temporal summation Size of fibers Large fibers produce more powerful movements Degree of muscle stretch Optimal resting length ______________________________________________ 73. Length Optimal length 80-120% of normal resting length Length-tension relationship ______________________________________________ 74. Velocity and Duration of Contraction Load / Recruitment / Muscle Fiber Type 75 - 76. ATP Requirements myosin energized break cross bridges pump calcium back into sarcoplasmic reticulum Sources Creatine phosphate/Oxidative phosphorylation/ Glycolysis Oxygen debt or deficit 77. Skeletal Muscle Fiber Types Differences in the speed of contraction fast-twitch fibers and slow-twitch fibers Differences in the primary mode of ATP production glycolytic fibers and oxidative fibers Slow oxidative, fast oxidative, and fast glycolytic fibers 78 - 79. Fast and Slow Fibers Dependent on rate of myosin ATPase activity ATP hydrolysis = rate limiting step of cycle Higher rate = faster crossbridge cycling Fast fibers Myosin with fast ATPase activity Slow fibers Myosin with slow ATPase activity 80 – 82. Oxidative and Glycolytic Fibers Based on primary source of energy Oxidative phosphorylation Many mitochondria Myoglobin (red) Small diameter Resistant to fatigue 83. Skeletal Muscle Fiber Types Slow oxidative Fast oxidative Fast glycolytic 84. Slow Oxidative Fibers Low myosin ATPase High oxidative capacity—aerobic Mitochondria Rich blood supply ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ Myoglobin (red) Small diameter Little tension Small diffusion barrier Fatigue slowly Myoglobin Slow to fatigue, but more rapid than slow oxidative Intermediate diameter 85. Fast Glycolytic Fibers High myosin ATPase activity High glycolytic capacity High glycogen stores Many glycolytic enzymes No myoglobin (white) Large diameter Greater tension Fatigue rapidly 86. Fast Oxidative Fibers High myosin ATPase activity High oxidative capacity—aerobic Myoglobin Slow to fatigue, but more rapid than slow oxidative Intermediate diameter ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ 87. Recruitment Order Slow oxidative fibers Fast oxidative fibers Fast glycolytic fibers ______________________________________________ 86. Adaptation Improved ATP-synthesizing activity Oxidative fibers Increased mitochondria Hypertrophy Increased diameter of glycolytic ifbers Increased mysoin/actin Testosterone Atrophy Disuse Denervation ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________ ______________________________________________
