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

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