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Chapter 12

Chapter 12. Muscles. About this Chapter. Muscle types What muscles do How muscles contract Contraction to locomotion Roles of smooth muscles. Muscles. Contract! Generate motion Generate force Generate heat Support. Muscular System Functions. Body movement (Locomotion)

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Chapter 12

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  1. Chapter 12 Muscles

  2. About this Chapter • Muscle types • What muscles do • How muscles contract • Contraction to locomotion • Roles of smooth muscles

  3. Muscles • Contract! • Generate motion • Generate force • Generate heat • Support

  4. Muscular System Functions • Body movement (Locomotion) • Maintenance of posture • Respiration • Diaphragm and intercostal contractions • Communication (Verbal and Facial) • Constriction of organs and vessels • Peristalsis of intestinal tract • Vasoconstriction of b.v. and other structures (pupils) • Heart beat • Production of body heat (Thermogenesis)

  5. Properties of Muscle • Excitability: capacity of muscle to respond to a stimulus • Contractility: ability of a muscle to shorten and generate pulling force • Extensibility: muscle can be stretched back to its original length • Elasticity: ability of muscle to recoil to original resting length after stretched

  6. Muscle Types • Cardiac – heart • Smooth – internal organs • Skeletal – "voluntary" • Attach to bone • Move appendages • Support body • Antagonistic pairs • Flexors • Extensors

  7. Types of Muscle • Skeletal • Attached to bones • Makes up 40% of body weight • Responsible for locomotion, facial expressions, posture, respiratory movements, other types of body movement • Voluntary in action; controlled by somatic motor neurons • Smooth • In the walls of hollow organs, blood vessels, eye, glands, uterus, skin • Some functions: propel urine, mix food in digestive tract, dilating/constricting pupils, regulating blood flow, • In some locations, autorhythmic • Controlled involuntarily by endocrine and autonomic nervous systems • Cardiac • Heart: major source of movement of blood • Autorhythmic • Controlled involuntarily by endocrine and autonomic nervous systems

  8. Categories of skeletal muscle actions • CategoriesActions • Extensor Increases the angle at a joint • Flexor Decreases the angle at a joint • Abductor Moves limb away from midline of body • Adductor Moves limb toward midline of body • Levator Moves insertion upward • Depressor Moves insertion downward • Rotator Rotates a bone along its axis • Sphincter Constricts an opening

  9. Connective Tissue Sheaths • Connective Tissue of a Muscle • Epimysium. Dense regular c.t. surrounding entire muscle • Separates muscle from surrounding tissues and organs • Connected to the deep fascia • Perimysium. Collagen and elastic fibers surrounding a group of muscle fibers called a fascicle • Contains b.v and nerves • Endomysium. Loose connective tissue that surrounds individual muscle fibers • Also contains b.v., nerves, and satellite cells (embryonic stem cells function in repair of muscle tissue • Collagen fibers of all 3 layers come together at each end of muscle to form a tendon or aponeurosis.

  10. Muscle Types Figure 12-1: Three types of muscles

  11. Muscle Tissue Types

  12. Skeletal Muscle Anatomy • About 40% body mass • Muscle fibers – cells • Fascicle – bundle • Motor unit • Muscle • sheath • Attach to tendons (which attach to bone)

  13. Nerve and Blood Vessel Supply • Motor neurons • stimulate muscle fibers to contract • Neuron axons branch so that each muscle fiber (muscle cell) is innervated • Form a neuromuscular junction (= myoneural junction) • Capillary beds surround muscle fibers • Muscles require large amounts of energy • Extensive vascular network delivers necessary oxygen and nutrients and carries away metabolic waste produced by muscle fibers

  14. Skeletal Muscle Anatomy Figure 12-3a-1: ANATOMY SUMMARY: Skeletal Muscle

  15. Skeletal Muscle Anatomy Figure 12-3a-2: ANATOMY SUMMARY: Skeletal Muscle

  16. Muscle Fiber Structure • Multiple nuclei • Sarcolemma • T-tubules • Sarcoplasmic reticulum • Sarcoplasm • Mitochondria • Glycogen & ions • Myofibrils

  17. Muscle Fiber Structure Figure 12-3b: ANATOMY SUMMARY: Skeletal Muscle

  18. Muscle Fiber Structure Figure 12-4: T-tubules and the sarcoplasmic reticulum

  19. Myofibrils: Site of Contraction • Actin – "thin fibers" • Tropomysin • Troponin • Myosin – "thick fibers" • Titin – elastic anchor • Nebulin – non-elastic

  20. Myofibrils: Site of Contraction Figure 12-3c-f: ANATOMY SUMMARY: Skeletal Muscle

  21. Sarcomere: Organization of Fibers • Z disks • I band • A band • H Zone • M line • Titin • Nebulin Figure 12-5: The two- and three-dimensional organization of a sarcomere

  22. Sarcomere: Organization of Fibers Figure 12-6: Titin and nebulin

  23. Skeletal Muscle Contraction: Mechanism Figure 12-11a: Excitation-contraction coupling

  24. Skeletal Muscle Contraction: Mechanism Figure 12-11b: Excitation-contraction coupling

  25. One Postulated Cause of Muscle Fatigue • Stress responses in skeletal muscle during E-C coupling. Stress-induced RyR1 dysfunction can result in SR Ca2+ leak, which potentially activates numerous Ca2+-dependent cellular damage mechanisms. AC, adenylate cyclase.

  26. Energy for Contraction: ATP & Phosphocreatine • Aerobic Respiration • Oxygen • Glucose • Fatty acids • 30-32 ATPs • Anaerobic Respiration • Fast but • 2 ATP/glucose • Phosphocreatine ATPs

  27. Energy for Contraction: ATP & Phosphocreatine Figure 12-13: Phosphocreatine

  28. Muscle Fatigue: Causes not well known • Central • "Feeling" • Lactic acid • Peripheral • Glycogen depletion • Ca2+ interference • High Pi levels • ECF high K+ • ACh depletion Figure 12-14: Locations and possible causes of muscle fatigue

  29. Fiber Contraction Speed: Fast Twitch • Rate • 2-3 times faster • SR uptake of Ca2+ • ATP splitting • Anaerobic/Fatigue easily • Power lifting • Fast/delicate • Sprint

  30. Fiber Contraction Speed: Fast Twitch Figure 12-15: Fast-twitch glycolytic and slow-twitch muscle fibers

  31. Fiber Contraction Speed: Oxidative Fast & Slow • Oxidative Fast Twitch • Intermediate speed • Anaerobic & aerobic • Slow Twitch: Aerobic, less fatigue • More mitochondria • More capillaries • Myoglobin • Endurance activities • Postural muscles

  32. Coordinating the Fibers: Force of Contraction • Excitation and Twitch • Length–Tension: more crossbridges: more tension Figure 12-16: Length-tension relationships in contracting skeletal muscle

  33. Coordinating the Fibers: Summation to Tetanus Figure 12-17: Summation of contractions

  34. Smooth Muscle • Fusiform cells • One nucleus per cell • Nonstriated • Involuntary • Slow, wave-like contractions

  35. Smooth Muscle • Cells are not striated • Fibers smaller than those in skeletal muscle • Spindle-shaped; single, central nucleus • More actin than myosin • No sarcomeres • Not arranged as symmetrically as in skeletal muscle, thus NO striations. • Caveolae: indentations in sarcolemma; • May act like T tubules • Dense bodies instead of Z disks • Have noncontractile intermediate filaments

  36. Smooth Muscle • Grouped into sheets in walls of hollow organs • Longitudinal layer – muscle fibers run parallel to organ’s long axis • Circular layer – muscle fibers run around circumference of the organ • Both layers participate in peristalsis

  37. Smooth Muscle • Is innervated by autonomic nervous system (ANS) • Visceral or unitary smooth muscle • Only a few muscle fibers innervated in each group • Impulse spreads through gap junctions • Whole sheet contracts as a unit • Often autorhythmic • Multiunit: • Cells or groups of cells act as independent units • Arrector pili of skin and iris of eye

  38. Smooth Muscle Cell

  39. Smooth Muscle Contraction: Mechanism

  40. Smooth Muscle Relaxation: Mechanism

  41. Contractile fibers are arranged in oblique bundles rather than in parallel sarcomeres

  42. Myosin of Smooth Muscle • Different isoform than that found in skeletal muscle • Smooth muscle myosin ATPase activity is much slower, contraction is longer • Myosin light chain in the myosin head regulates contraction and relaxation

  43. Smooth Muscle • Relatively little sarcoplasmic reticulum • Lacks T-tubules • Chemically linked to the cell membrane, rather than mechanically linked • Ca +2 storage is supplemented by caveolae , small vesicles that cluster close to the cell membrane. Voltage/ligand gated Ca +2 channels

  44. Single-Unit Muscle

  45. Gap junctions Pacemaker cells with spontaneous depolarizations Innervation to few cells Tone = level of contraction without stimulation Increases/decreases in tension Graded Contractions No recruitment Vary intracellular calcium Stretch Reflex Relaxation in response to sudden or prolonged stretch Properties of Single-Unit Smooth Muscle

  46. Multi-Unit Muscle

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