The Musculoskeletal System (Edexcel International A Level Biology)

Revision Note






The Musculoskeletal System

  • 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)

Muscle pair

Antagonistic muscle action: the two muscles work together by pulling in opposite directions

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Author: Marlene

Marlene graduated from Stellenbosch University, South Africa, in 2002 with a degree in Biodiversity and Ecology. After completing a PGCE (Postgraduate certificate in education) in 2003 she taught high school Biology for over 10 years at various schools across South Africa before returning to Stellenbosch University in 2014 to obtain an Honours degree in Biological Sciences. With over 16 years of teaching experience, of which the past 3 years were spent teaching IGCSE and A level Biology, Marlene is passionate about Biology and making it more approachable to her students.