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Muscle PowerPoint Presentation

Muscle

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Muscle

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  1. Muscle Chapter 17

  2. Movement • Locomotion • Movement of animal from one location to another • Repositioning • Movement of animal appendages • Internal movement • Movement of gases, fluids and ingested solids through the animal

  3. Muscle Tissue • Specially designed to physically shorten (contract) • Generates mechanical force • Functions • locomotion and external movements • internal movement (circulation, digestion) • heat generation

  4. Muscle Types • Skeletal Muscle • large muscle fibers (cells) • striated (banded) • voluntary control • Cardiac Muscle • striated • fibers linked by intercalated disks (electrical synapses) • self-excitation • Smooth Muscle • small tapered fibers • lack striations Figs 17.1, 17.18, and 17.19

  5. Skeletal Muscle Organization • Muscle fibers (cells) • elongate cells, parallel arrangement • sarcolemma – cell membrane • sarcoplamic reticulum (SR) • membraneous internal network • Stores Ca2+ • linked to sarcolemma by transverse tubules Fig 17.1

  6. Skeletal Muscle Organization • myofibrils - intracellular contractile elements • Arranged in sarcomeres (repeated tandem units) • Consist of myofilaments • thick filaments (myosin) • thin filaments (actin) Fig 17.1

  7. Thick Filament Structure • Bundles of several hundred myosin molecules • intertwining tails + globular heads • heads contain • actin binding sites • ATP-hydrolyzing sites • form crossbridges with actin Fig 17.4

  8. Thin Filament Structure • Actin • Primary structural protein • Spherical protein subunits connected in long, double strand • Contains myosin binding site • Tropomyosin • Threadlike proteins • Normally cover myosin binding sites • Troponin • Ca2+ Binding Protein • Holds tropomyosin in place • Ca2+ binding induces shape change that repositions tropomyosin Fig 17.6

  9. Skeletal Muscle Contraction:Sliding Filament Mechanism • Movement of thin filaments over thick • thick filaments are stationary; thin are dragged across thick • sarcomere shortening by increasing overlap of thick and thin filaments Fig 17.3

  10. Crossbridge Cycling • Myosin head binds to actin • Cross bridge bends (Power Stroke) • thin filaments pulled toward center of sarcomere • Cross bridge link broken • Cross bridge ‘unbends’ and binds to next actin molecule Fig 17.5

  11. Neural Activation of Skeletal Muscle Contraction • Excitation-Contraction Coupling • Events that link muscle excitation to muscle contraction • Excitation = Action Potential • Brief, rapid depolarization of cell membrane. • Triggers release of Ca2+ into the cytosol of the muscle fiber

  12. Neural Input • Action potential travels down axon to terminal • Exocytosis of acetylcholine (ACh) • ACh diffuses across cleft • ACh opens ACh-gated Na+ channels • Action potential propagates down sarcolemma Fig 17.7

  13. Excitation-Contraction Coupling • T-tubules conduct APs into the cell • Triggers Ca2+ channels in SR to open • Ca2+ released into the cytosol Fig 17.7

  14. Smooth Muscle Contraction • No striations • contractile proteins not arranged in sarcomeres • arranged in fish-net network • allows for extensive contraction, even when stretched Fig 17.18

  15. Smooth Muscle Excitation-Contraction Coupling • Depolarization of sarcolemma opens Ca2+ channels • Ca2+ enters the cell from the extracellular fluid • Ca2+ binds with calmodulin in cytoplasm • Ca2+-calmodulin binds to myosin light chain kinase • activates MLCK • MLCK phosphorylates myosin • needed for myosin to bind actin • Cross-bridge cycling

  16. Whole Muscle Mechanics Types of Contractions • Isometric Contraction • muscle is prevented from shortening • contraction generates force on attachment points • Isotonic Contraction • muscle allowed to shorten upon contraction • muscle moves and object of a given mass Fig 17.9

  17. Isometric Contractions Twitch • response to a single, rapid stimulus Summation • Application of stimuli in rapid succession • Muscle responds to second before fully relaxed from first • Increased tension generated Tetanus • With repeated stimulation at high frequency twitches fuse to form steady tension Fig 17.11

  18. Length-Tension Relationship • Maximum force generated is associated with starting length of muscle • Related to the overlaps of thick and thin filaments • Maximum tension generated at normal in vivo resting length • Too long - pull thick and thin filaments apart • Too short - thin filaments form opposite sides collide Fig 17.12

  19. Isotonic Contraction • Muscle free to shorten with stimulation •  shortening distance with load •  shortening velocity with load Fig 17.9-17.10

  20. Isotonic Contraction • Contraction Force (N) • Anything that changes the state of motion for an object • Force  Cross-Sectional Area • Work (J) • Expresses forces applied to an object to set it in motion • Force × Distance • With  load,  mass,  distance • Max work obtained at ~40% max. load • Work  Muscle Mass Fig 17.13

  21. Comparative Muscle Physiology:Vertebrate Skeletal Fiber Types • Fast (Twitch) Fibers • Low myoglobin content (white) • used for rapid movements • large nerve fibers w/ high velocities • anaerobic activity • Slow (Tonic) Fibers • High myoglobin content (red) • used for low-force prolonged contractions • small nerve fibers w/ low velocities • aerobic activity Fig 17.15 Table 17.2

  22. Comparative Muscle Physiology:Fiber Types in Tuna • Tonic Fibers • located in lateral core areas • used for “cruising” • Twitch Fibers • much of the remaining muscle mass • used for short bursts of high activity

  23. Comparative Muscle Physiology:Molluscan Catch Muscle • Used to seal shells of bivalves • Sustained contraction w/o fatigue • Little  in O2 consumption • Two groups of neurons innervate muscle • Exciters - releases ACh • causes release of Ca2+ • binds myosin w/o release • Relaxers - releases seratonin • causes release of cAMP • causes Ca2+ release from myosin

  24. Comparative Muscle Physiology:Crustacean Chelipod Muscle • Pinnate (angular) arrangement of fibers • can have more, shorter fibers • 2x increase in force • Few or only single motor unit(s) per muscle • Multiple innervation to each muscle fibers • slow neuron - stimulates tonic activity • fast neuron - stimulates twitch activity • inhibitory neuron - restricts activity Fig 17.17

  25. Comparative Muscle Physiology:Insect Flight Muscle • Synchonous flight muscle • moths, grasshoppers, dragonflies • slow wingbeat frequencies • each contraction is a response to a single nerve impulse • Asynchronous flight muscle • flies, bees mosquitoes • high wingbeat frequencies (100-1000 bps) • too fast for response to individual nerve signals • multiple contractions per nerve signal Box 17.2

  26. Comparative Muscle Physiology:Asynchronous Muscle Function • Fibrillar muscles • attached to walls of thorax • horizontal arrangement • vertical arrangement • not connected to wings • distort shape of thorax Box 17.2

  27. Comparative Muscle Physiology:Asynchronous Muscle Function • upstroke • vertical muscles contract • thorax distorted (click) • stretch horizontal muscles • induced them to contract • downstroke • horizontal muscles contract • distort thorax • stretch vertical muscles • several wingbeats per nerve impulse Box 17.2

  28. Comparative Muscle Physiology:Electric Eels • Electric organs – modified skeletal muscle • Electrocytes – stacked in columns • Respond to signals from motor neurons • All electrocytes in column depolarize spontaneously • Up to 600 V discharge Box 17.1