Edexcel A (SNAB) A Level Biology:复习笔记7.1.1 Movement of the Skeleton

• 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