The Cause of The Contraction Movement

Identify that the cause of the contraction movement is the formation of temporary bonds between the actin and myosin fibres and explain why ATP is consumed in this process

  • The ATP used by the myosin puts the myosin into a higher energy state and causes it to move and bond with the actin. It bonds onto the actin and pulls itself along like a ratchet.
  • When Ca2+ sets off a muscle contraction, actin and myosin bind together via cross-bridges. These cross-bridges form in such a way that the actin filaments are pulled along past the myosin filaments. The actin and myosin filaments slide past each other and overlap each other.
  • The chemical energy of ATP is released as mechanical energy to actively move the actin. The myosin catalyses the breakdown of ATP as it binds to actin.
  • The bonds between the actin and myosin are temporary and are released as the Ca2+ ion concentration decreases and the muscle relaxes again.
  • Upon contraction, the sarcomere decreases in size. Only the lighter bands within the sarcomere decrease in size. Actin and myosin filaments do not change size. They simply slide past one another.