Skeletal System

  • it consist of three main types of tissues;
  • muscles
  • bones
  • cartilage

Functions of the skeletal system

  • protection
  • Support
  • Muscle attachment
  • movement
  • storage of calcium
  • blood cells formation

Main types of skeletal system;

  • exoskeleton in insects
  • its functions include support, attachment of muscle for movement, protection and prevent water loss
  • endoskeletons in vertebrates(eg humans)
  • its functions include support, protection and movement


Skeleton of Humans

  • it is divided into three parts:
  • Axial skeleton-skull, back bone and ribs
  • Appendicular skeleton-limbs
  • Girdles-hip and shoulder girder


Pectoral girdle- shoulder


  • Shoulder
  • a triangular, flat bone witha shallow cavity on narrower end. It joins the arm tto the axial skeleton.
  • The collar bone
  • it prevents the shoulder from bending inward.
  • Arm – upper and lower arm
  • Ulna and radius
  • ulna is longer and thicker than radius
  • has cavity where part of humorous fitted to make a hinge joint
  • ulna has an extended bone
  • Humorous
  • A long bone with a rounded head-epiphysis and a long central shaft-endophysis
  • Shallow cavity
  • lose attachment oof the shoulder bone with the back side of ribs



Is a connection between two or more joints. They provide articulation between bones making movement possible.

Types of joints

Gliding joint

  • e.g joints which occur between the vertebrate wrists and ankles
  • the ends of the bones that make the joint are covered with cartilage
  • they are held together by tough ligaments


Synovial joint

  • it is enclosed by fibrous capsule lined by synovial membrane which secretes synovial fluid into the synovial cavity
  • the synovial fluid lubricates the joint
  • they include hinge and ball and socket joints


Hinge joint

  • eg knee joint
  • it allows movement in one plane, ball and socket joint
  • eg hip joint;
  • it allows rotation in all directions


Role of muscles in movement of human arm

Muscles that bring about movement are antagonistic i.e when one set contracts the other relaxes

  • Movement of the hinge joint of an arm
  • moving arm upwards(biceps flexor) muscle contract whilst triceps muscle relax
  • straightening the arm, biceps muscle relaxes whilst the triceps(extensor) muscle contract


Antagonistic muscle of human forelimb


  • the biceps muscles of the forelimb act as flexors while the triceps muscle act as extensors
  • the biceps has its points of origin on the scapula and the point of insertion on the radius
  • the triceps has its point of origin on the scapula and humorous and is inserted on the ulna
  • when the muscles contract, the limb act as a lever with the pivot at the joint
  • contraction of biceps muscles bends the arms while contractions of triceps extend the arm

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