muscle tissues

• Characteristics of Muscle Tissue

  • Contractility
  • Excitability
  • Extensibility
  • Elasticity

  
• Muscular System

  Embryonic origin: mesoderm (except iris of the eye - ectoderm)
• Unicellular Contractile Cells

  • Myoepithelial cell
  • Pericytes
  • Myofibroblasts
• Muscle Tissue


  • Skeletal Muscle
  • Cardiac Muscle
  • Smooth Muscle

  
• Skeletal Muscle

  • Movement of skeleton, eye globe, and tongue

  
• Cardiac Muscle

  • Rhythmic contractions of heart
• Smooth Muscle


  • Visceral muscle (blood vessels, GIT, uterus)

  
• Skeletal Muscle Structure: Connective Tissue Investments

  1. Epimysium

  2. Perimysium

  3. Endomysium

  
• Skeletal Muscle Cells

  • Arise from fusion of myoblasts
  • Differentiate from mesenchymal cells
  • Myosatellite cells (stem cells)
  • Long, cylindrical, multinucleated

  
• Sarcolemma

  Plasma membrane
• Sarcoplasm

  Cytoplasm
• Sarcoplasmic Reticulum

  Smooth ER
• Sarcosomes

  Mitochondria
• Muscle Fiber Nuclei

  • Oval shape
  • Numerous (up to hundreds)
  • Peripheral location near sarcolemma

  
• Myofibrils


  Bundles of thick and thin myofilaments
• Myofibrils

  • About 5,000-10,000 per muscle fiber
  • Span the length of the muscle fiber
  • Exhibit striations

  
• Striations

  Alternating dark (A-bands) and light (I-bands) bands
• Sarcomere

  Region between two adjacent Z-discs, functional unit of contraction
• Sarcomere

  • Size: 1.5 to 2 μm (resting)
  • Up to 10,000 in each myofibril
• Myofilaments

  • Thick Myofilaments (Myosin)
  • Thin Myofilaments (Actin, Tropomyosin, Troponin)
• Thick Myofilaments


  • Diameter: 10-15 nm
  • Length: 1.5-1.6 μm
  • Occupy A-band
  • Protein: Myosin
• Thin Myofilaments


  • Diameter: 5-6 nm
  • Length: 1.0 μm
  • Actin filaments (F-actin)
  • Tropomyosin
  • Troponin
• Myofilament Arrangement

  • Hexagonal, 1 thick filament surrounded by 6 thin filaments
• Triad

  • T-tubule (transverse invaginations of sarcolemma)
  • Pair of terminal cisternae (modified smooth ER)
• Neuromuscular Junction


  • Motor neuron sends axon fibers to sarcolemma
  • Motor endplate (point of contact of axon terminal and sarcolemma)
  • Acetylcholine (ACh) released from axon terminal

  
• Proprioceptive Organs


  • Neuromuscular spindle (stretch receptor)
  • Golgi tendon organ (activated when muscle contracts too strenuously)
• Muscle Fiber Types


  • Red
  • White
  • Intermediate

  
• Cardiac Muscle


  • Cylindrical, shorter cells
  • Striations present
  • Sarcomeres present
  • Dyads (T-tubule and cistern)
  • Involuntary, rhythmic contraction
  • Branching fibers
  • Intercalated discs (desmosomes, gap junctions)
• Smooth Muscle


  • Fusiform, tightly packed cells
  • No striations or sarcomeres
  • Involuntary, slow and steady contraction
  • Caveolae, dense bodies, criss-cross myofilament arrangement
  • Fewer myosin cross-bridges
  • Calmodulin and myosin light-chain kinase

  
• Repair and regeneration of muscle tissue