Lesson 3 Chapter 8 – Skeletal System

Lesson 3 Chapter 8 – Skeletal System [Articulations] Unit 3 Study Guide Excluded from your studies: The joints of the hand – page 227 – 228 Articulations A joint is a point of articulation between two or more bones, especially such a connection that allows motion.  Point of contact  between 2 bones  between cartilage and bone  between teeth and bones Classifications of Joints  Fibrous joints  Cartilaginous joints  Synovial joints Fibrous Joints These joints are also called "fixed" or "immoveable" joints, because they do not move. These joints have no joint cavity and are connected via fibrous connective tissue. The skull bones are connected by fibrous joints. Cartilaginous Joints These joints also have no joint cavity and the bones are connected tightly to each other with cartilage. These joints only allow a small amount of movement, so are also called "partly" or "slightly moveable" joints. The vertebrae are examples of cartilaginous joints. Synovial Joints Most of the joints in the body are synovial joints. These joints are "freely moveable" and are characterised by being surrounded by an articular capsule which contains the synovial fluid. Synovial fluid lubricates the joints, supplies nutrients to the cartilage and it contains cells that remove microbes and debris within the joint cavity. Because of the larger range of movements of these joints, there is an increased risk of injury eg. dislocations. Synovial joints are located predominantly in limbs. Many synovial joints also have ligaments either inside or outside the capsule. 1 Lesson 3 Chapter 8 – Skeletal System [Articulations] The range of movement provided by these joints is determined by:   The closeness of the bones at the point of contact. Closer bones make stronger joints, but movements are more restricted. The looser the fit, the greater the range of movement. However, looser joints are more prone to dislocation. The flexibility of the connective tissue and the position of the ligaments, muscles and tendons. Different Types of Synovial Joints There are six different types of synovial joints: gliding, hinged, pivot, condyloid, saddle, and ball and socket. They are the most common forms of joint in the body. All are free moving, have a wide range of motion and are surrounded by a substance known as synovial fluid. 2 Lesson 3 Chapter 8 – Skeletal System [Articulations] 3 Gliding Gliding joints have the most simplistic range of motion of all synovial joints. They function to allow side-to-side and back-and-forth motions. An example of a gliding joint would be the vertebrae, which allow the spine to bend or lean to the side. Bones adjoining with gliding joints are typically flat but may have a slightly curved, concave, or convex appearance. Hinged Hinged joints permit a back-and-forth motion, allowing parts of the body to extend and flex. With this particular joint, one bone must be concave and the other convex to allow the most extensive range of motion. An example of a hinged joint would be the knee. The knee joint permits the shin and foot to swing inward and outward, allowing the motions used in running, walking, and swimming. Pivot A pivot joint is limited to circular motions. Its joint is composed of a depressed bone and another cone-shaped bone that provide the ability to twist or rotate. Examples include the radius and ulna (primary bones in the forearm). These allow the forearm to turn, providing the motions necessary for pronation and supination. Condyloid Like gliding joints, condyloid joints provide a similar side-to-side and up-and-down motion. Condyloid joints contain one concave bone and another oval-shaped bone. They are also known as biaxial joints, which means they maintain two separate axes (left to right, up and down). An example of a condyloid joint would be the radiocarpal joint of the wrist. Saddle Saddle joints are similar to condyloid joints in that they contain a concave and convex bone that fit snugly together. However, saddle joints provide a much wider range of motion. The carpometacarpal joint at the base of the the thumb is a good example. This allows the thumb to be opposable, providing additional motions that other fingers do not have. Ball and Socket Ball and socket joints provide the greatest range of motion for the body. They are composed of one rounded or convex bone that fits into a cupped depression or hole in another bone. An example of a ball and socket joint would be the shoulder. Lesson 3 Chapter 8 – Skeletal System [Articulations] 4 Note: Ligaments connect bone to bone - ligament - tough regularly arranged connective tissue, slightly elastic. Tendons connect muscle to bone - tendon - non-elastic, flexible, connective tissue which allows the muscle to pull on the bone to create a movement. The tendon at the none-moving end of a muscle is called the tendon of origin, at the moving end of a muscle it is called the tendon of insertion.