The Structural basis of movement

• Muscle contraction processes:

  • Treppe (staircase effect): repeated increase in strength of contraction due to successive stimulations
  • Summation: more motor units stimulated lead to more muscle fibers contracting, producing greater strength
  • Tetanus: rapid stimulation frequency making relaxation impossible (spasm)
  • Fatigue: decrease in work capacity due to muscle compression of blood vessels causing decreased blood supply (ischemia)
  • Rigor: depletion of ATP prevents Ca+ sequestration back into the sarcoplasmic reticulum, hindering muscle fiber relaxation
  • Rigor mortis: similar to rigor but sets in a few hours after death and is a permanent condition
• Muscle contraction mechanism:

  • Initiated by the generation of an action potential on the sarcolemma at the neuromuscular junction
  • Depolarization of the sarcolemma leads to a localized current flow extended over the sarcolemma
  • T-tubules are inward continuations of the sarcolemma, passing through myofibrils between A- and I-bands
  • Release of Ca++ from the sarcoplasmic reticulum triggers actin and myosin filament linking, leading to muscle contraction
  • ATP is crucial for muscle relaxation, as without it, the muscle cannot relax
• Types of muscle contractions:

  • Concentric contraction: muscle fibers shorten
  • Eccentric contraction: extension of the fibers
  • Isometric contraction: length remains unchanged but tension increases
  • Isotonic contraction: tension remains the same, but length changes
• Types of muscle tissues:

  • Skeletal muscles (striated or voluntary)
  • Cardiac muscles (striated but involuntary)
  • Smooth muscles (visceral or involuntary)
• Characteristics of muscle tissues:

  • Skeletal muscles: multinuclear cells with stripes, covered by sarcolemma, myofibrils with myosin and actin filaments
  • Smooth muscles: long, spindle-shaped cells with a single nucleus, actin and myosin filaments present but not in striations
• The skeletal system is made up of bones, cartilage, ligaments, tendons, joints, and muscles.
• Bones are hard structures that protect organs and support the body.
• Cartilage is a flexible connective tissue found at the ends of long bones to cushion them during movement.