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Chapter 12b

Chapter 12b. Muscles. Summation of Contractions. Figure 12-17a. Summation of Contractions. Figure 12-17b. Summation of Contractions. Figure 12-17c. Summation of Contractions. Figure 12-17d. Motor Units. One muscle may have many motor units of different fiber types. SPINAL CORD.

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Chapter 12b

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  1. Chapter 12b Muscles

  2. Summation of Contractions Figure 12-17a

  3. Summation of Contractions Figure 12-17b

  4. Summation of Contractions Figure 12-17c

  5. Summation of Contractions Figure 12-17d

  6. Motor Units One muscle may havemany motor units ofdifferent fiber types. SPINAL CORD Neuron 1 Neuron 2 Neuron 3 Motornerve KEY Motor unit 1 Muscle fibers Motor unit 2 Motor unit 3 Interactive Physiology® Animation: Muscular System:Contraction of Motor Units PLAY Figure 12-18

  7. Mechanics of Body Movement • Isotonic contractions create force and move load • Concentric action is a shortening action • climbing • Eccentric action is a lengthening action • Downhill skiing, going down stairs • Isometric contractions create force without moving a load • Series elastic elements; sarcomeres shorten while elastic elements stretch resulting in little change in overall length

  8. Isotonic Contraction Figure 12-19a

  9. Isometric Contraction Figure 12-19b

  10. Series Elastic Elements in Muscle Schematic of the series elastic elements Elasticcomponents Tricepsmuscle 1 2 3 Contractilecomponents Elasticelement Bicepsmuscle Muscle length Sarcomeres Isotonic contraction:Sarcomeres shortenmore but, because elasticelements are alreadystretched, the entiremuscle must shorten. Isometric contraction:Muscle has not shortened.Sarcomeres shorten, generatingforce, but elastic elementsstretch, allowing muscle lengthto remain the same. 1 Muscleat rest 2 3 Figure 12-20

  11. The Arm is a Lever and Fulcrum System (a) Biceps muscle Lever Load Fulcrum Figure 12-21a

  12. The Arm is a Lever and Fulcrum System (b) F1 F2 = 2 kg 5 cm 15 cm Figure 12-21b

  13. The Arm is a Lever and Fulcrum System (c) A 7-kg load is addedto the hand 25 cmfrom the elbow. D1 5 cm D2 25 cm Figure 12-21c

  14. The Arm Amplifies Speed of Movement of the Load Lever 5 cm 1 cm Fulcrum Figure 12-22

  15. Load-Velocity Relationship in Skeletal Muscle Figure 12-23

  16. Muscle Disorders • Muscle cramp: sustained painful contraction • Overuse • Disuse/Atrophy • Acquired disorders • Inherited disorders • Duchenne’s muscular dystrophy • Dystrophin • McArdle’s disease • Myophosphorylase deficiency glycogenosis – glycogen not converted to glucose 6-phosphate

  17. Duration of Muscle Contraction in the Three Types of Muscle Skeletal Cardiac Smooth Tension 5 0 1 2 3 4 Time (sec) Figure 12-24

  18. Smooth Muscle • Contraction and relaxation slower • Uses less energy • Maintains force for long periods • Low oxygen consumption

  19. Smooth Muscle • Smooth muscle is not studied as much as skeletal muscle because • It has more variety • Anatomy makes functional studies difficult • It is controlled by hormones, paracrines, and neurotransmitters • It has variable electrical properties • Multiple pathways influence contraction and relaxation

  20. Types of Smooth Muscle Autonomic neuronvaricosity Smallintestine Gapjunctions Neuro-transmitter Smooth musclecell Receptor (a) Single-unit smooth muscle cells Figure 12-25a

  21. Smooth Muscle • Much smaller than skeletal muscle fibers • Has longer actin and myosin filaments • Myosin ATPase activity much slower • Myosin light chain plays regulatory role • Not arranged in sarcomeres • Has less sarcoplasmic reticulum • IP3-receptor channel is the primary calcium channel • Calcium also enters cell from extracellular fluid

  22. Cardiac Muscle • Shares features with both skeletal and smooth muscle • Like skeletal: • Striated; sarcomere structure • Unlike skeletal: • Muscle fibers shorter; may be branched; have single nucleus • Like smooth: • Electrically linked to one another; some exhibit pacemaker potentials; under sympathetic and parasympathetic control as well as hormone control

  23. Muscle Summary Table 12-3

  24. Muscle Summary • Skeletal muscles • Origin, insertion, flexors, extensors, and antagonistic muscles • T-tubules, sarcoplasmic reticulum, myofibrils, thick filament, thin filament, actin, myosin, and crossbridges • Sarcomere, Z disks, I bands, A band, H zone, and M line • Muscle tension, load, sliding filament theory, tropomyosin, troponin, Ca2+-ATPase, myosin ATPase, power stroke, rigor state

  25. Summary • Skeletal muscle • Excitation-contraction coupling, DHP receptors, and Ca2+ release channels • Twitch, latent period, phosphocreatine, and muscle fatigue • Muscle fiber types, myoglobin, tetanus, and motor unit • Mechanics of body movement • Isotonic versus isometric contractions • Series elastic elements, levers, and fulcrums

  26. Summary • Smooth muscle • Types of smooth muscle, IP3-receptor channel, calmodulin, myosin light chain kinase, myosin light protein chains, and myosin phosphatase • Myogenic contraction, slow wave or pacemaker potentials, and pharmacomechanical coupling • Cardiac muscle • Comparison to other muscle types

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