Types of Muscle

  • Smooth
    • Does not require conscious
    • Found in walls of internal organs (excluding heart)
    • g. Intestines, blood vessels
  • Cardiac
    • Does not require conscious
    • Found only in the heart
  • Skeletal (striated/striped/voluntary)
    • Requires conscious
    • Controls mobility
    • g. biceps, triceps

Skeletal Muscle

  • Skeletal muscle is attached to bones via tendons
  • Ligaments attach bones to another bone
  • Pairs of skeletal muscles work antagonistically at the joints
  • The bones act as levers, allowing the muscles to pull against them
  • Skeletal muscle is made up of bundles of muscle fibres
    • Cell membranes of muscle fibre cells is the sarcolemma
  • Transverse Tubules are the folds of the sarcolemma inwards across the muscle fibre and into the sarcoplasm (cytoplasm)
    • Transverse tubules help to spread electrical impulses through the sarcoplasm so all parts of the muscle fibre is reached equally
  • Sarcoplasmic reticulum is a network of internal membranes which through the sarcoplasm
    • Sarcoplasmic reticulum stores and releases Ca2+
  • There is high number of mitochondria to provide adequate ATP
  • Muscle fibres are multinucleate (many nuclei)
  • They have lots of myofibrils
    • Long cylindrical organelles which are made up of proteins which are specialised for muscle contraction


  • Contain bundles of thick and thin myofilaments which can slide past each other
    • Thick myofilament is Myosin (dark band)
    • Thin myofilament is Actin (light band)

A band) some overlapping thick and thin filaments

I band) Only contains (thin) actin filament

H Zone) Only contains myosin filaments

Z line) End of each sarcomere

M line) Middle of the myosin filament

Sliding Filament Theory

  • Muscle contraction occurs due to sliding filaments
  • Myosin and actin filaments slide over one another to make the sarcomere contract
  • Myofilaments do no contract.
  • The larger amount of simultaneous sarcomere contractions results in the muscle fibres and myofibrils contracting
  • Sarcomeres return to original length after on relax