• The?effective movement?of the human body requires both?muscle?and an?incompressible skeleton
  • This is because muscles will only produce effective movement if they?pull on a structure?that does not shorten or bend - bone
• There are over 600 skeletal muscles in the human body
• Muscles are?effectors, stimulated by nerve impulses from motor neurones
• The muscular system is complex, with multiple muscles crossing over each other in multiple directions
• Lengths of?strong connective tissue?called?tendons, connect muscles to bones
  • They are flexible but do not stretch when a muscle is contracting and pulling on a bone
  • There are a few muscles with very long tendons and also a few that are directly attached to the bone
• Ligaments?are also lengths of?strong connective tissue?but they?connect bones to other bones, which keep the skeleton intact

Antagonistic muscle action

• Muscles are only capable of?contracting?or?pulling,?they?cannot push
• As a result of this limitation muscles generally operate in?pairs
• A muscle pulls in one direction?at a joint?and the other muscle?pulls in the opposite direction
  • This is described as?antagonistic?muscle action
• An example of this can be seen in the biceps and triceps of the arm
• To raise the lower arm
  • The?bicep contracts?and the?tricep relaxes
  • As the bone can't be stretched the arm?flexes around the joint
  • A muscle that bends a joint during contraction is known as a?flexor?(the bicep in this case)
  • This brings the tricep into its full length so that it can contract again
• To lower the lower arm
  • The?tricep contracts?and?bicep relaxes
  • As the bone can't be stretched the arm?flexes around the joint
  • A muscle that straightens a joint during contraction is known as an?extensor?(the tricep in this case)

Antagonistic muscle action: the two muscles work together by pulling in opposite directions