Muscle Tissue Notes

Muscle Tissue

  • A primary tissue type, divided into:
    • Skeletal muscle tissue
    • Cardiac muscle tissue
    • Smooth muscle tissue

Functions of Skeletal Muscle Tissue

  • Skeletal Muscles
    • Are attached to the skeletal system
    • Allow us to move
  • The muscular system
    • Includes only skeletal muscles
  • Six Functions of Skeletal Muscle Tissue
    • Produce skeletal movement
    • Maintain posture and body position
    • Support soft tissues
    • Guard entrances and exits
    • Maintain body temperature
    • Store nutrient reserves

Organization of Muscle

  • Skeletal Muscle
    • Muscle tissue (muscle cells or fibers)
    • Connective tissues
    • Nerves
    • Blood vessels
  • Organization of Connective Tissues
    • Muscles have three layers of connective tissues
      • Epimysium
      • Perimysium
      • Endomysium

Epimysium

  • Exterior collagen layer
  • Connected to deep fascia
  • Separates muscle from surrounding tissues

Perimysium

  • Surrounds muscle fiber bundles (fascicles)
  • Contains blood vessel and nerve supply to fascicles

Endomysium

  • Surrounds individual muscle cells (muscle fibers)
  • Contains capillaries and nerve fibers contacting muscle cells
  • Contains myosatellite cells (stem cells) that repair damage

Muscle Attachments

  • Endomysium, perimysium, and epimysium come together:
    • At ends of muscles
    • To form connective tissue attachment to bone matrix
      • I.e., tendon (bundle) or aponeurosis (sheet)

Blood Vessels and Nerves

  • Muscles have extensive vascular systems that:
    • Supply large amounts of oxygen
    • Supply nutrients
    • Carry away wastes
  • Skeletal muscles are voluntary muscles, controlled by nerves of the central nervous system (brain and spinal cord)

Characteristics of Skeletal Muscle Fibers

  • Skeletal Muscle Cells
    • Are very long
    • Develop through fusion of mesodermal cells (myoblasts)
    • Become very large
    • Contain hundreds of nuclei

Formation of Multinucleate Skeletal Muscle Fiber

  • Muscle fibers develop through the fusion of mesodermal cells called myoblasts.

Structure of a Skeletal Muscle Fiber

  • Includes myofibrils, sarcolemma, sarcoplasm, nuclei, and mitochondria.

Structural Components of a Sarcomere

  • Sarcomeres
    • The contractile units of muscle
    • Structural units of myofibrils
    • Form visible patterns within myofibrils
      • A striped or striated pattern within myofibrils
      • Alternating dark, thick filaments (A bands) and light, thin filaments (I bands)

Levels of Functional Organization in a Skeletal Muscle

  • Sarcomere
    • Contains thick filaments, thin filaments, Z line, M line, Titin, H band, I band, A band

Sarcomere Structure

  • Includes I band, A band, H band, Z line, Titin, Zone of overlap, M line, Sarcomere with Thin filament and Thick filament indications

Structural Components of a Sarcomere - Thin Filaments

  • F-actin (filamentous actin)
    • Is two twisted rows of globular G-actin
    • The active sites on G-actin strands bind to myosin
  • Nebulin
    • Holds F-actin strands together
  • Tropomyosin
    • Is a double strand
    • Prevents actin–myosin interaction
  • Troponin
    • A globular protein
    • Binds tropomyosin to G-actin
    • Controlled by Ca2+Ca^{2+}

Thick and Thin Filaments

  • Organization of G-actin subunits in an F-actin strand, and the position of the troponin–tropomyosin complex
  • Structure of a myosin molecule: includes the Myosin head, Myosin tail, and Hinge.
  • Structure of thick filaments: showing the orientation of the myosin molecules with indication of the M line.