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
