Joints: Structural and Functional Classifications

• Bones in the skull are connected by fibrous joints called sutures, fibrous joints also connect bones in the lower leg (fibulas and tibias) and teeth in their sockets, these are called gomphoses.
• Structural classification of joints includes three types:
  • Fibrous joints: connect bones with fibrous tissue.
  • Cartilaginous joints: connect bones with cartilage, can be rigid or slightly movable, e.g. synchondrosis and symphysis.
  • Synovial joints: connect bones with dense connective tissue and a fluid-filled joint cavity, allowing for free movement.
• Functional classification of joints based on the amount of movement:
  • Synarthroses: non-moving joints.
  • Amphiarthroses: slightly-moving joints.
  • Diarthroses: freely-moving joints.
• Synovial joints have six special features:
  • Articular cartilage covering opposing bone surfaces.
  • Joint (articular) cavity.
  • Fibrous joint (articular) capsule.
  • Synovial fluid in the cavity acting as a lubricant.
  • Bandlike ligaments for reinforcement.
  • Sensory nerve fibers and blood vessels in the joint capsule and synovial membrane.
• Six types of synovial joints:
  • Gliding: allows for gliding movements when one flat bone surface glides over another. Examples: intercarpal joints in the wrist and intertarsal joints in the ankle.
  • Hinge: only moves in one direction, allows for angular movements like flexion and extension. Examples: elbow and interphalangeal joints in the fingers.
  • Pivot: allows for rotation and twisting movements. Examples: where the humerus meets the radius and ulna at the elbow.
  • Condylar: allows for movements like flexion, extension, abduction, and adduction. Example: in the wrist.
  • Saddle: allows for opposition movements as well as flexion, extension, abduction, and adduction. Example: thumb joints.
  • Ball and socket: allows for a lot of maneuverability and allows for rotational movements, abduction, adduction, flexion, and extension. Examples: shoulder and hip joints.
• Muscles aid in the movement of joints by contracting, they can't move bones directly.
• Muscle contractions have two main types:
  • Isotonic: causes a change in the length of the muscles.
  • Isometric: no change in length.
• Muscles have an insertion, the movable bone during a muscle contraction, and an origin, the bone that moves less or not at all.

Other types of movements at different joints:

• Circumduction: moving a limb in a circle.
• Elevation and depression: lifting and lowering a body part superiorly.
• Protraction and retraction: Ex. Sticking the jaw out and back in.
• Dorsiflexion and plantar flexion: lifting the foot up and down at the ankle.
• Inversion and eversion: turning the foot towards or away from the midline of the body.