Muscles

• Muscles attach to bones via tendons
• Muscle belly is the region of contraction
• Origin: usually the proximal or medial tendon, attached to bone
• Insertion: tendon crossing the joint, attaching to bone, skin or connective tissue
• Excitability: responds to stimulation
• Extensibility: stretches beyond resting length
• Elasticity: returns to resting length
• Contractility: contracts to generate tension at the ends
• Aponeurosis: tendinous tissue running through the muscle
• Tendon transfer force from muscle to skeleton
• 3 layers of fascia:

  1. Epimysium
  2. Perimysium
  3. Endomysium
• Epimysium: encases the muscle fibre bundle
• Perimysium: encases the fascicle
• Endomysium: encases individual muscle fibre cells
• Myofibrils are contractile apparatus made of many sarcomeres, encased in the sarcolemma
• Actin is the thin filament
• Myosin is the thick filament
• Z line: start and end point of a single sarcomere
• A band: where actin and myosin overlap
• I band: contains actin only
• H zone: contains myosin only
• Force in a muscle is proportional to the number of cross bridges formed
• Sliding Filament Theory:

  1. AP travels along sarcolemma
  2. AP enters cell through T Tubules, triggering release of Ca2+ into the cell
  3. Ca2+ binds with troponin, unlocking tropomyosin on actin filaments
  4. Myosin heads bind with actin, forming cross bridges
  5. Myosin heads undergo a power stroke
  6. ATP fuels pumping Ca2+ back into sarcoplasmic reticulum to reset