Muscles and Muscle Tissue Summary

OVERVIEW OF MUSCLE TISSUE

  • Comprises nearly half of body mass
  • Converts chemical energy (ATP) into mechanical energy

TYPES OF MUSCLE TISSUE

  • Prefixes: Myo and sarco relate to muscle
  • Types:
    • Skeletal Muscle: Striated, voluntary, rapid contraction, tires easily
    • Cardiac Muscle: Striated, involuntary, found in heart, pacemaker initiates contraction
    • Smooth Muscle: Non-striated, involuntary, found in hollow organs

CHARACTERISTICS OF MUSCLE TISSUE

  • Excitability: Responds to stimuli
  • Contractility: Can shorten forcibly upon stimulus

MUSCLE FUNCTIONS

  • Produces movement (locomotion, manipulation)
  • Maintains posture
  • Stabilizes joints
  • Generates heat during contraction

SKELETAL MUSCLE ANATOMY

  • Contains nerve and blood supply
  • Features connective tissue sheaths: Epimysium, Perimysium, Endomysium
  • Muscles attach to bones via insertion (movable) and origin (immovable)

MUSCLE FIBER MICROANATOMY

  • Composed of myofibrils, sarcoplasmic reticulum, T tubules
  • Myofibrils: Contains striations, sarcomeres, myofilaments
  • Sarcomere: Smallest contractile unit, composed of A bands and I bands

SARCOPLASMIC RETICULUM AND T TUBULES

  • SR: Regulates Ca2+ levels
  • T Tubules: Increase surface area, allowing nerve impulses to penetrate the fiber

SLIDING FILAMENT MODEL OF CONTRACTION

  • Thick and thin filaments slide past each other; neither changes length
  • Contraction occurs when cross bridges between actin and myosin form

NERVE STIMULUS AND NEUROMUSCULAR JUNCTION

  • Muscle fibers stimulated by somatic motor neurons
  • Acetylcholine (ACh) released, causing action potential in sarcolemma

GENERATION OF ACTION POTENTIAL

  • Depolarization: Triggered by Na+ influx
  • Repolarization: Restoration of resting potential through K+ efflux

EXCITATION-CONTRACTION COUPLING

  • Electrical stimulation leads to Ca2+ release and muscle contraction

FACTORS AFFECTING MUSCLE CONTRACTION

  • Number of muscle fibers stimulated, size of fibers, frequency of stimulation, degree of stretch

SMOOTH MUSCLE CONTRACTION

  • Lacks striations, contracts slower but more efficiently
  • Contraction regulated by autonomic nervous system and local chemical changes
  • Unique mechanism involving calmodulin for Ca2+ regulation

ENERGY FOR MUSCLE CONTRACTION

  • ATP required for cross bridge cycle and Ca2+ management
  • Regenerated via:
    • Direct phosphorylation by creatine phosphate
    • Anaerobic glycolysis
    • Aerobic respiration