Muscular system

• Myology


  The scientific study of muscles
• Muscle types


  • Skeletal
  • Cardiac
  • Smooth
• Skeletal muscle


  • Striated, voluntary
• Cardiac muscle


  • Striated, involuntary
• Smooth muscle


  • Non-striated, involuntary
• Functions of muscular tissue

  • Producing body movements
  • Stabilizing body positions
  • Regulating organ volume
  • Moving substances within the body
  • Releasing heat
• Epimysium


  Covering an entire muscle
• Perimysium


  Covering fascicles
• Endomysium


  Covering individual muscle fibres
• Tendons


  Extensions of connective tissue beyond muscle fibres that attach the muscle to bone
• Skeletal muscles are well supplied with nerves and blood vessels, which provide nutrients and oxygen for contraction
• Muscle fasciculi


  Groups of skeletal muscle fibres
• Skeletal muscle


  Many muscle fasciculi joined together
• Skeletal muscle fibre


  Multinucleated cell that acts as a single contractile unit
• Sarcolemma


  Plasma membrane that encloses the entire skeletal muscle fibre
• Transverse tubules (T-tubules)


  Tunnels that extend from the surface toward the center of each muscle fibre, connected with sarcoplasmic reticulum on either side to form a triad
• Sarcoplasm


  Fluid-filled space within a skeletal muscle fibre
• Myofibrils


  Contain thin and thick filaments
• Sarcomere


  Functional unit of striated muscle fibres
• Thick filaments


  Contain myosin
• Thin filaments


  Contain actin, tropomyosin, and troponin
• Sarcoplasmic reticulum


  Specialised endoplasmic reticulum present in skeletal muscle fibres, stores calcium ions
• Terminal cisternae


  Dilated terminal sacs of the sarcoplasmic reticulum
• 1. tubule


  Invagination of the sarcolemma, lies between the two terminal cisternae to form a triad
• Triad


  Structure formed by the two terminal cisternae and the t-tubule in between them
• Myosin heavy chains


  Coiled around each other to form a double helix that forms the tail of myosin thick filaments
• Myosin heads


  Globular structures at the end of the myosin heavy chains, with two light chains
• Actin


  Protein that forms thin filaments, has an ADP active site for cross-bridge formation
• Tropomyosin


  Protein wrapped around actin in thin filaments, covers the active sites and prevents cross-bridge formation in resting state
• Troponin


  Protein attached to tropomyosin, initiates the process of skeletal muscle contraction when calcium ions bind to it
• Z discs


  Zig-zagging zones of dense protein material that separate sarcomeres
• A band


  Darker area extending the entire length of the thick filaments
• H zone


  Narrow area at the center of the A band, contains only the thick filaments
• I band


  Lighter-coloured area to either side of the A band, contains the thin filaments but no thick filaments
• Blood vessels lie between the fascicles, and each muscle is supplied by many capillaries, reducing the diffusion distance
• Pump function of skeletal muscle

  Veins embedded within a muscle are compressed during contraction, causing an increase in blood pressure due to one-way valves, driving blood towards the heart
• Muscle action potential


  Electrical signal delivered by a motor neuron that stimulates a skeletal muscle fibre to contract
• Motor unit


  Single motor neuron and all the muscle fibres it stimulates
• Neuromuscular junction (NMJ)


  Synapse between a motor neuron and a skeletal muscle fibre
• Voltage-gated calcium channels


  In the terminal axon, open when the axon terminal is depolarized by the nerve impulse