The Muscular System

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The Muscular System
2012-02-27 17:22:27
Muscular System Human anatomy

The human muscular system
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  1. Muscular System
    • composed of skeletal muscles only
    • study of is called myology
  2. Skeletal Muscle
    voluntary striated muscle that is usually attached to one or more bones
  3. Striations
    • exhibits microscopic pattern of alternating light and dark bands
    • result from overlapping arrangement of contractile proteins within each cell
    • about 100um in diameter and 3 cm long
  4. Muscle Fibers
    • aka myofibers
    • typical skeletal mscles that have extraordinary length
  5. Cardiac Muscle
    • Also Striated
    • involuntary
    • short stumpy cells
  6. Cardiocytes
    • aka myocytes
    • short stumpy cells like logs with notched ends
    • commonly only about 80um long by 15 um wide
  7. Smooth Muscle
    • involuntary
    • lacks striations, hence name
    • contains same contractile proteins but not arranged in regularly overlapping way
    • thick in middle and tapered at ends
    • avg about 200um long by 5um wide
  8. Functions of Muscle
    • Movement
    • Stability
    • Control of body openings and passages
    • Heat production
    • Glycemic control
  9. Universal Properties of Muscle
    • Excitability (responsiveness)
    • Conductivity
    • Contractility
    • Extensibility
    • Elasticity
  10. Endomysium
    • thin sleeve of loose connective tissue that surrounds each muscle fiber
    • creates room for blood capillaries and nerve fibers to reach e/ muscle fiber
    • provides extracellular chem environ for muscle fiber and assoc. nerve ending
    • excitation based on xchange of calcium, sodium and ptassium ions tween tissue fluid and nerve and muscle fibers
  11. Perimysium
    • thicker connective tissue sheat that wraps muscle fibers 2gether in bundles called fascicles
    • fascicles- visible to naked eye as parallel strands
  12. Epimysium
    • fibrous sheath that surrounds entire muscle
    • outer surface grades into fascia and inner surface issues projections tween fascicles to form perimysium
  13. Fascia
    • sheet of connective tissue
    • separates neighboring muscles of muscle groups from each oterh and from subcutaneous tissue
    • muscles grouped in compartments sep from e/ o/ by fascia
  14. Fusiform Muscles
    • thick in middle tapered at end
    • ex- biceps brachii and gastrocnemius
    • relatively strong
  15. Parallel Muscles
    • fairly uniform width and parallel fascicles
    • some are elongated straps (rectus abdominis)
    • some squarish and are called quadrilateral msucles (masseter of jaw)
    • can span long dist and shorten more than o/ muscle types
    • produce less force
  16. Triangular (Convergent) Muscles
    • Fan-shaped
    • ex-pectoralis major
    • relatively strong cause of large number of fibers in wider part of muscle
  17. Pennate Muscles
    • feather shaped
    • fascicles insert obliquely on tendon
    • Three types;
    • unipennate, fascicles approach tendon from one side
    • bipennate, fascicles approach tendon from both sides
    • multipennate, shpaed like bunch of feathers with quills converging on single point

    generate more force than others cuze they fit more muscle fibers into given length of muscle
  18. Circular Muscles (sphincters)
    • form rings around certain body openings
    • contract, constrict opening and tend to prevent passage of material thru itex- eyelids
  19. Indirect attachment
    • ends conspicuously short of bony destination
    • gap bridged by fibrous band or tendon
  20. Aponeurosis
    • broad sheet of tendon
    • refers to tendons assciated with certain ab, lumbar, hand and foot muscles
  21. Direct (fleshy) attachment
    So little separation between muscle and bone that to the naked eye, red muscular tissue seems to emerge directly from bone
  22. Origin
    site of attachment at relatively stationary end
  23. Insertion
    attachment site at more mobile end
  24. Belly
    middle, usually thicker region
  25. Antagonist
    • muscle opposing primary mover
    • maintains sum tension on joint and limits speed or range of prime mover
  26. prime mover (agonist)
    muslce that produces most of force during particular joint action
  27. Action
    effect produced by muscle to produce or prevent movement
  28. synergist
    muscle that aids prime mover
  29. antagonistic pair
    act on opposite sides of a joint
  30. fixator
    muscle that prevents a bone from moving
  31. intrinsic muscle
    • entirely contained within particular region
    • both origin and sertion there
  32. extrinsic muscle
    actws upon designated region but its origin is elsewhere
  33. lever
    any elongated, rigid object that rotates around a fix point
  34. Fulcrum
    fixed point rotated around by lever
  35. Rotation
    occurs when an effort overcomes a resistance (load)
  36. effort arm
    part of lever from the flucrum to point of effort
  37. Resistance arm
    part from the fulcrum to the point of resistance
  38. Mechanical advantage (MA)
    • ratio of its output force to its input force
    • equal to length of the effort
    • LE= effort arm, LR= resistance arm
    • MA=LE/LR
  39. First-class lever
    • one with the fulcrum in the middle (EFR)
    • like a seesaw
    • atlanto-occipital joint of neck, muslces of back of neck pull down on occipital bone of skull and oppose tendency of head to tip forward
  40. Second-class lever
    • one in which resistance in middle (FRE)
    • Wheelbarrow
    • mandible, digastric muscle pulls down on chin to open mouth, fulcrum is temporomandibular join-effort is digastric muscle and resistance is tension of muscles like temporalis muscle
  41. Third-class lever
    • effort applied between fulcrum and resistance
    • paddling cannoe
    • effort applied to middle of shaft and resistance produced by water against blade, relatively stationary grip at upper end of paddle
    • most musculoskeletal levers are 3rd class
  42. Sarcolemma
    plasma membrane of muscle fiber
  43. Sarcoplasm
    • Cytoplasm of muscle fibers
    • occupied by long protein bunderls, (myofibrils)
    • abundance of glycogen-starchlike carbohydrate that provides energy for cell during periods of heightened excercise
    • red pigment myoglobin-stores oxygen till needed for muscular activity
  44. sarcoplasmic reticulum
    • smooth endoplasmic reticulum
    • forms network around each myofibril
  45. terminal cisternae
    dilated end-sacs of sarcoplasmic reticulum
  46. transverse (t) tubules
    • formed when sarcolemma turns inward at many points
    • penetrate thru cell and emerge on other side
    • carries 2 electrical signals from cell surface into interior and induces gates in SR membrane to open
  47. Myofilaments
    • parallel protein microfilaments
    • makes up myofibrils
    • 3 Kinds; Thick filaments, thin filaments, elastic filaments
  48. Thick filaments
    • made of several hundred molecules of myosin protein
    • bundle of 200-500 myosins
  49. Thin filaments
    • composed primarily of two intertwined strands of protein
    • called fibrous (f) actin- like bead necklace
    • also contains protein tropomyosin- has smaller calcium-binding protein called troponin
  50. Elastic Filaments
    • made of huge springy protein titin (connectin)
    • helps to stabilize thick filament, center it tween thin filaments and prevent overstretching
  51. Contractile Proteins
    • myosin and actin
    • do work of shortening muscle fiber
  52. Regulatory proteins
    • tropomyosin and troponin
    • act like switch to determine when fiber can contract and when it cannot
  53. dystrophin
    • enormous protein located just under sarcolemma
    • links actin filaments to transmembrane proteins in sarcolemma
  54. A bands
    • dark bands in striated muscle
    • consists of thick filaments lying side by side
  55. I bands
    Light bnads in striated muscle
  56. H band
    • thin filaments do not reach
    • in middle of A band
  57. M line
    thick filaments originate at a dark M line
  58. Z disc (line)
    • bisect I band
    • provides anchorage for thin filaments and elastic filaments
  59. Sarcomere
    • functional contractile unit of muscle fiber
    • muscle shortens because its individ sarcomeres shorten and pull z discs closer to each other and dystrophin and the linking proteins pull on the extracellular proteins of muscle
  60. synapse
    any point where a nerve fiber meets and stimulates another cell
  61. Somatic motor fibers
    • lead to the skeletal muscles
    • axons of cell bodies of somatic motor neurons
  62. Neuromuscular junction (NMJ)
    • aka motor end plate
    • nerve fiber approaches and individ muscle fiber and branches again to establish sever points of cantact within NMJ
    • each terminal branch of nerve fiber within NMJ forms synapse with uscle fiber
    • sarcolemma of NMJ is irregularly indented
    • one nerve fiber stimulates muscle fiber at several points within each NMJ
  63. Synaptic knob
    • end of nerve fiber at each synapse
    • doesnt directly touch muslce fiber but is separated from it by a narrow space called synaptic cleft
  64. synaptic vesicles
    filled with chemical called acetycholine (ACh) when a when nerve signal arrives at synaptic knob, some of these vesicles release their ACh by exocytosis
  65. ACh receptors
    respond to ACh by inititating electrical devents that lead to muscle contraction
  66. Junctional Folds
    increase membrane surface area in sarcolemma and allow for more ACh receptors, thus allow more sensitivity of muscle fiber to nervous stimulation
  67. Acetylcholinesterase (AChE)
    • enzyme that is found in both sarcolemma and basal lamina
    • breaks down ACh after the ACh has stimulated muscle cell
    • import in turning off muscle contraction
  68. motor unit
    • group of muscle fibers innervated by one nerve fiber
    • not clustered together but dispersed throughout muslce
    • when stimulated cause weak contraction over wide area, not just localized twitch in small region
    • effective muscle contraction usually requires activation of several motor units aqt once
    • abg about 200 fibers per motor neuron
    • mult motor units in muscle= they can "work in shifts", also mena strength can be controlled
  69. Excitation
    • nerve fiber releases ACh, which excites mucle fiber
    • wave of electrical excitation spreads into the sarcoplasm by way of T tubules
  70. Excitation- contraction coupling
    • consists of events that link this electrical stimulus to the onset of muscle tension
    • Excitation of the T tubules induces the sarcoplasmic reticulum to release calcium ions, and calcium clears way for myosin of thick filaments to bind the actin of the thin filaments
  71. Contraction
    myosin heads reepeatedly attach to the thin filaments and pull on them, cause the thin filaments to slide across the thick filaments and shorten the cell
  72. Relaxation
    nerve signaling ceases, myosin once again blocked from binding to actin and muscle tension subsdies
  73. Slow Oxidative (SO) fibers
    • aka slow-twitch, red or type I fibers
    • relatively abundant mitochondria, myoglobin and blood capillaries. felatively deep red color
    • do not faituge easily: well adapted to aerobic respiration, way to make ATP that requires oxygen but does not generate lactic acid- majore contributor to muscle fatigue
    • exhibit a relatively long twitch or contraction
  74. fast glycolytic (FG) fibers
    • aka fast-twitch, white, or type II fibers
    • rich in enzymes for anaerobic fermentation, process that is independent of oxygen but produces lactic acid
    • respond quickly but fatigue more easily than SO
    • poorer in mitochondria, myoglobin and blood capillaries, relatively pale
    • well adapted for quick responses but not endurance
  75. Intermediate fibers
    • combine fast-twitch responses with aerobic fatigue-resistant metabolism(sub fg fibers)
    • relatively rare except in in some endurance-trained athletes
  76. intercalated discs
    • dark lines in cardiac muscle that exhibits characteristic dark lines where cells meet
    • like steplike regions allow cells to communicate with each other
  77. dense bodies
    instead of z discs, little masses of protein scattered throughout the sarcoplasm and on inner face of the sarcolemma
  78. Multiunit smooth muslce
    occurs in some of the largest arteries and pulmonary air passages, in piloerector muscles of hair follicles and in iris of eyehas a motor unit, but contracts independently of others
  79. Single-unit smooth muscle
    • more widespread
    • occurs in most blood vessels and in digestive, respiratory, urinary and reproductive trachts- thus also called visceral muscle
    • nerve fibers in this type of muscle do not synapse with individ muscle cells but pass thru tissue and exhibit swellings called varicosities at which they release neurotransmitters, thus directly stimulating each other almost as if they were a single cell
  80. smooth muscle tone
    maintains blood pressure by keeping blood vessels partially constricted and it prevents such organs as stomach, intestines, urinary bladder and uterus from becoming flaccid when empty
  81. Peristalsis
    waves of contraction made by smooth muscle that propel contents through an organ (esophagus)
  82. satellite cells
    • stem cells that persist throughout life
    • some fuse with growing muscle fibers and contribute nuclei to it through childhood
    • may regenerate a limited amount of damaged skeletal muscle even in adults
  83. Myopathies
    diseases of muscular tissue
  84. Muscular dystrophy
    • collective term for several hereditary diseases in which skeletal muscles degenerate, lose strength, and are gradually replaced by fat and scar tissue
    • the new connective tissue impedes blood circulation which in turn accelerates muscle degeneration creating a fatal spiral of positive feedback
  85. Myasthenia gravis (MG)
    • most prevalent in women from 20-40 years old
    • autimmune disease in which antibodies attack neuromuscular junctions and trigger destruction of ACh receptors
    • muscle fibers bcome less and less sensitive to ACh
    • effects often appear first in facial muscles and include drooping eyelids and doble fision
    • often followed by difficulty swallowing, weakness of the limbs, and poor physical endurance
    • some die quickly as a result of respiratory failur, while others have normal life span