Muscles Pairs

• • 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
• The two muscles work together by pulling in opposite directions

  A) tendons

  B) contracts

  C) raise

  D) relaxes

  
• • 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