muscular tissue

• Bones


  • Provide leverage and form the framework of the body
  • Cannot move body parts by themselves
• Motion


  Results from the alternating contraction and relaxation of muscles
• Muscles make up 40–50% of total adult body weight (depending on the percentage of body fat, gender, and exercise regimen)
• Muscular strength


  Reflects the primary function of muscle—the transformation of chemical energy into mechanical energy to generate force, perform work, and produce movement
• Muscle tissues


  • Stabilize body position
  • Regulate organ volume
  • Generate heat
  • Propel fluids and food matter through various body systems
• Muscular Tissue


  Contributes to homeostasis by producing body movements, moving substances through the body, and producing heat to maintain normal body temperature
• Functions of Muscular Tissue

  • Producing body movements
  • Stabilizing body positions
  • Storing and moving substances within the body
  • Generating heat
• Muscular tissue


  • Electrical excitability
  • Contractility
  • Extensibility
  • Elasticity
• Skeletal muscle tissue is striated and works mainly in a voluntary manner

  
• Cardiac muscle tissue is striated and its action is involuntary
• Smooth muscle tissue is located in the walls of hollow internal structures, lacks striations, and its action is usually involuntary

  
• Connective tissue surrounds and protects muscular tissue
• Connective tissue layers surrounding skeletal muscle

  • Epimysium
  • Perimysium
  • Endomysium

  
• The epimysium, perimysium, and endomysium are all continuous with the connective tissue that attaches skeletal muscle to other structures

  
• Skeletal muscle is composed of hundreds to thousands of muscle fibers (cells)

  
• Sarcoplasm


  The cytoplasm of a muscle fiber, containing glycogen and myoglobin

  
• Mitochondria lie in rows throughout the muscle fiber, strategically close to the contractile muscle proteins

  
• Skeletal muscle fiber


  • Diameter ranges from 10 to 100 μm
  • Typical length is about 10 cm, some up to 30 cm
  • Has hundreds of nuclei due to fusion of myoblasts during development
  • Loses ability to undergo cell division after fusion
• Sarcolemma


  Plasma membrane of a muscle cell
• Transverse (T) tubules


  Tiny invaginations of the sarcolemma that tunnel in from the surface toward the center of each muscle fiber

  
• Sarcoplasm


  Cytoplasm of a muscle fiber, contains glycogen, myoglobin, and mitochondria

  
• Myofibrils


  Contractile organelles of skeletal muscle, about 2 μm in diameter and extend the entire length of a muscle fiber

  
• Sarcoplasmic reticulum (SR)


  Fluid-filled system of membranous sacs that encircles each myofibril
• Terminal cisterns


  Dilated end sacs of the sarcoplasmic reticulum that butt against the transverse tubules
• Triad


  A transverse tubule and the two terminal cisterns on either side of it
• Sarcomere


  The basic functional unit of a myofibril, extends from one Z disc to the next
• Components of a sarcomere

  • Z disc
  • A band
  • I band
  • H zone
  • M line
• Thick filaments


  16 nm in diameter, 1-2 μm long, composed of the protein myosin
• Thin filaments


  8 nm in diameter, 1-2 μm long, composed of the protein actin
• Myosin


  The main component of thick filaments, functions as a motor protein
• Actin


  The main component of thin filaments
• There are two thin filaments for every thick filament in the regions of filament overlap
• Calcium ions (Ca2+) are released from the terminal cisterns of the sarcoplasmic reticulum to trigger muscle contraction
• Muscular hypertrophy is the enlargement of existing muscle fibers due to increased production of myofibrils, mitochondria, and sarcoplasmic reticulum

  
• Muscular atrophy is a decrease in size of individual muscle fibers due to progressive loss of myofibrils
• H zone


  Narrow region in center of each A band that contains thick filaments but no thin filaments
• A band


  Dark, middle part of sarcomere that extends entire length of thick filaments and includes those parts of thin filaments that overlap thick filaments
• Zone of overlap


  Region where thin and thick filaments overlap
• I band


  Lighter, less dense area of sarcomere that contains remainder of thin filaments but no thick filaments
• Z disc


  Narrow, plate-shaped regions of dense material that separate one sarcomere from the next