voluntary and involuntary muscles

• types of muscle:

  • skeletal
  • cardiac
  • involuntary (smooth)
• skeletal muscle - muscles under conscious control, often attached to bone to enable movement
• Cardiac muscle - unique to the heart, cells are myogenic which means they can contract without a nervous impulse
• involuntary/smooth muscle - found in the walls of hollow organs like blood vessels which are controlled by the autonomic system
• Skeletal muscle

  • striated
  • conscious (voluntary)
  • regularly arranged so muscle contracts in one direction
  • rapid contraction speed
  • short length of contraction
  • tubular
  • multi-nucleated
• cardiac muscle

  • striated (fainter than skeletal muscle)
  • involuntary
  • cells branched and interconnected
  • intermediate contraction speed
  • intermediate length of contraction
  • uni-nucleated
  • myogenic
• involuntary/smooth muscle

  • non-striated
  • involuntary
  • no regular arrangement - different cells can contract in different directions
  • slow contraction speed
  • long length of contraction
  • uni-nucleated
• sarcolemma - cell surface membrane of a muscle fibre
• sarcoplasm - cytoplasm of a muscle fibre
• Transverse (T) tubules - extensions of the sarcolemma that transmit electrical signals, to ensure the entire muscle receives the impulse to contract simultaneously.
• sarcoplasmic reticulum - responsible for storing and releasing calcium ions, the folds are called cisternae
• myofibrils - subcellular structures designed for contraction
• myofibrils are made up of repeating units to form a sarcomere
• myofibrils are made up of:

  actin filaments - thinner filaments, consists of two strands twisted around each other

  myosin filaments - thicker filament, consists of long rod shapes with bulbous heads that project to the side
• key sections of the sarcomere:

  A band (Dark) - actin and myosin filaments

  I band (light) - just actin

  H zone - just myosin

  Z line - marks the boundaries of each sarcomere unit

  
• in contraction:

  • A band stays the same length
  • I band gets smaller
  • H zone gets smaller