muscles

• Muscular system


  Contractile tissues found in animals, which moves a particular bone, part, or substance of the body

  
• Muscular system


  • Muscles make things happen
  • Apply force for movement and together with skeletal system are the movers and levers of an animal
• Functions of the muscular system

  • Supply force for movement
  • Act upon visceral organs
  • Produce heat
• Muscle


  1. Refers to muscle tissue (muscle tissue and their endomysium)
  2. Refers to the whole organ plus associated with connective tissue, nerves and blood supply

  
• Muscle cell


  The active contractile component of a muscle organ
• Muscle fiber


  Tiny, frayed strands, which in fact are long individual muscle cells

  
• Belly (gaster)


  Fleshy part of the muscle and its ends that join the skeleton or adjacent organs form attachments
• Endomysium


  A layer of connective tissue that lightly wraps around each muscle cell

  
• Perimysium


  Sheath of connective tissue that wraps around groups of muscle cell

  
• Epimysium


  An outer coat of connective tissue that surrounds the entire muscle organ

  
• Fascicle


  Bundle of muscle cells defined by its particular perimysium

  
• Tendons


  Cordlike structures, mostly collagen fibers, often cross a joint because of their toughness and small size
• Aponeuroses


  Sheetlike structures that attach muscles indirectly to bones, cartilages, or connective tissue coverings

  
• Fascia


  On the outside of the epimysium
• Motor unit


  One motor neuron and all the skeletal muscle cells stimulated by that neuron

  
• In skeletal muscle, contraction involves chemical cross-bridges that form and reform between thick and thin filaments to ratchet or slide these filament past one another
• Red muscle fibers


  • Highly vascularized and rich in myoglobin
• White muscle fibers


  • Less vascularized
• Tonic fibers


  Slow contractions that produce low force, but can sustain contraction for prolonged periods of time
• Twitch (phasic) fibers


  Produce fast contractions used for rapid movements

  
• Types of fast twitch fibers

  • Fast twitch, fatigable (FF)
  • Fast twitch, resistance (FR)
  • Fast twitch, intermediate (FI)

  
• Differences in contraction speeds seem related to differences in myosin types in the fibers, to differences in the breakdown of ATP, and to differences in nervous innervation
• Slow twitch fibers


  • Used for muscular endurance, contract slowly but do not fatigue easily, use oxygen for aerobic respiration, have a large amount of mitochondria and many blood vessels, red in colour

  
• Fast twitch fibers


  • Used for muscular strength, contract rapidly but fatigue easily, respire anaerobically and consequently possess less mitochondria and have fewer blood vessels, lighter in colour (white)

  
• Active component


  Contributes to the total force
• Flexible component


  Contributes to the overall muscle force
• Total force output of a muscle organ is based on the active contractile machinery and the elastic component residing in connective tissue

  
• Running over level ground at constant speed

  Leg muscles need to shorten only very little to keep the animal moving, muscles and tendons absorb and release mechanical energy to maintain cyclical movements of the limbs and support the body mass
• Running up at incline, or sprinting


  More muscle is recruited and muscle shortening may be great to produce needed force
• Passive tension


  Force required to stretch the relaxed muscle to greater lengths and results from the elastic constituents of the muscle

  
• Total tension


  Measured at different lengths during contraction, sum of active and elastic components
• Active tension


  Contributed by the active component alone
• Graded force


  Wave of electrical depolarization arriving from the nerve and spreads to the muscle fiber to reach a threshold level for a muscle twitch to occur, force increases as the rate of arriving nerve impulses increases

  
• Motor unit


  A single motor neuron together with the muscle fibers it innervates

  
• Anatomical cross-sectional area (ACSA)


  The cross-sectional area of a muscle perpendicular to its longitudinal axis at its thickest part

  
• Physiological cross-sectional area (PCSA)


  The cross-section area of all muscle fibers perpendicular to their longitudinal axes

  
• Parallel muscle


  All fibers lie along the line of tension generated
• Pinnate muscle


  Fibers that lie oblique to the line of force generated, allows packing of more muscle fibers in the same space and shorter fibers

  
• Velocity of Shortening


  The absolute velocity traveled by the point of insertion is greater in a long muscle than in a short muscle, since longer muscles have more sacromeres in series

  
• Distance of Shortening


  As single sacromeres shorten, their distance or travel is added to that of adjoining sacromeres in series, so the additive effect is greater in a long muscle than in short muscle