muscle structure

• skeletal muscle 


  • form fibres which are multinucleated
  • movement
  • postural support
  • heat production
  • found all over the body - body contains 400 skeletal muscles
  • voluntary
  • contracts and relaxes
• cardia muscle 


  • long fibres which branch to form cross- bridges between fibres
  • found in the heart - cells joined by intercalated discs - allow diffusion of ions between cells
  • involuntary
  • contracts at steady rate
• smooth muscle


  • tapered and contracts slowly and regularly - controlled by autonomic nervous system
  • tubular structures arranged longitudinally and circularly
  • involuntary
  • walls of hollow organs
• sarcoplasm


  muscle cell cytoplasm
• sarcoplasmic reticulum


  specialised endoplasmic reticulum - storage sites for calcium
• sarcolemma


  membrane that surrounds muscle fibre
• neuromuscular junction


  • site where motor neuron meets muscle fibre - separated by gap called neuromuscular cleft
  • motor end plate
  • pocket formed around motor neuron
• motor unit


  • some motor neurones stimulate single muscle fibres.
  • many motor neurones divide and connect to several muscle fibres
  • all these muscle fibres contract together, providing a stronger contraction
  • variables affecting strength and degree of muscle movement

  1. number of motor units firing
  2. number of muscle cells per motor unit
• • myosin only in H zone
  • centre of an A band is the M line
  • centre of the I band is a Z line
  • I band = where there is only actin it looks lighter
  • A band = where myosin and actin overlap the myofibril looks dark
• • M line = middle
  • H zone = contracts and relaxing
  • thin = actin
  • thick = myosin
  • tropysin = myosin grabs and pulls in