Joints

• Functions of joints:

  • Supports the body
  • Permits/ decreases bone movement
  • Facilitates growth
• Hinge joints: The convex surface of one bone fits into the concave surface of another.

  • Allow for movement in one plane only
  • E.g elbow and knee
• Ball and socket joints: The spherical head of one bone fits into a cup cavity of another.

  • 360 degree range of motion called 'circumduction'
  • E.g shoulder and hip
• Gliding joints: Usually occurs at flat bones.

  • Any direction in a side to side motion or a back and forth motion
  • E.g carpals and tarsals
• Pivot joints: Formed when the rounded, pointed, or conical end of one bone articulates with a ring, formed partly by bone and partly by ligament.

  • Twisting motion
  • E.g first vertebrae on which the head is balanced
• Saddle joints: One bone is concaved and the other bone is convexed. They fit together like a saddle.

  • Side to side motion or a back and forth motion
  • E.g where the thumb joins the palm of the hand
• Condyloid joints: One surface is slightly convex which fits into a slightly concaved depression of another.

  • Up and down movement and side to side movement
  • E.g between metatarsal bones and phalange of toes
• Structure of synovial joints:

  • Synovial Cavity: The space between articulating bones in a synovial joint
  • Articular Capsule: The sac like envelope enclosing the cavity of a synovial joint
  • Synovial Fluid: The fluid that fills the cavity of a synovial joint. It removes debris, absorbs shock, and reduces friction
  • Articular Cartilage: Covers the articulating surfaces of bones at a joint. It allows for smooth movement
  • Bursae: Little sacs of fluid that prevent friction in a moveable joint
  • Accessory Ligaments: Ligaments that hold bones together and prevent dislocation
• Fibrous/ fixed joint examples:

  • Skull
  • Joints between teeth and jaw
• Cartilaginous joint examples:

  • Discs in between vertebrae
  • Ribs and sternum joints