• 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

   

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 bicep and tricep 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
  • 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

   

The two muscles work together by pulling in opposite directions

• Muscles?maintain posture?by antagonistic muscles?both contracting at joints?to keep the joint at a certain angle
  • This is known as?isometric contraction?- a muscle contraction without motion

   

• Whenever?lifting heavy objects?the contraction process is more complicated with more muscles involved
  • For example,?multiple muscles are involved?in enabling the hand to grip, allowing the wrist to rotate and stabilising the shoulder
  • This is a?complex process?of coordination involving the?brain