Muscle Pairs (AQA A Level Biology)

Muscle 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

• 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