Notes Ch. 8a Joints of the Skeletal System Anatomy and Physiology

Types of Joints Joints are structures that connect bones. They can be classified by the type of tissue that binds the bones at each junction. The 3 general groups are fibrous joints, cartilaginous joints, and synovial joints. Joints can also be classified by movement. In this case they can be classified as immovable, slightly movable, and freely moveable.

Fibrous Joints Fibrous joints are named so because they have many collagen fibers. These joints are between bones in close contact. There are 3 types of fibrous joints: Syndesmosis - bones are bound by a sheet or bundle of dense connective tissue. The joints is flexible. An example of this joint is between the tibia and fibula.

2. Sutures - are only between flat bones of the skull, where broad margins of adjacent bones grow together and will form a layer of dense connective tissue, called a sutural ligament.

3. Gomphosis - a joint formed by the union of a cone-shaped bony process and a bony socket. Where a tooth is fastened to the mandible is this type of joint.

Cartilaginous Joints Cartilaginous joints are when hyaline cartilage or fibrocartilage connects bones. There are 2 types: Synchondrosis - Bones of hyaline cartilage unite the bones. Many of these joints are temporary and disappear during growth. An example would be the part of an immature long bone where a band of hyaline cartilage connects the ends.

2. Symphysis cover the surface of the bone that is covered by a thin layer of hyaline cartilage. Limited movement happens at this joint. An example is the pubic symphysis between the pubic bones of the pelvis.

Synovial Joints Most of the joints found in the skeletal system are synovial joints. They allow free movement. They are made of articular cartilage, a joint capsule, and a synovial membrane (which secretes synovial fluid).

General Structure of a Synovial Joint The ends of bones in a synovial joint are covered with a thin layer of hyaline cartilage. This layer, the articular cartilage, resists wear and minimizes friction when it is compressed as the joint moves. A joint capsule holds together the bones of the joint. The outer layer is made of dense connective tissue. This area is flexible to allow movement and strong enough to help prevent the bones from being pulled apart.

Ligaments, bundles of strong, tough collagen fibers reinforce the joint capsule and help bind the end of the bones. These ligaments helps prevent excess movement at the joint. The ligament will tighten when the joint is stressed. The inner layer of the joint capsule is made of a synovial membrane. This secretes synovial fluid. The synovial membrane sometimes stores adipose tissue, it can reabsorb fluid. The fluid is very important for lubricating the joint. It also gives nutrients to the joint.

Some synovial joints are partially or completely divided into 2 compartments by discs of fibrocartilage called menisci. The knee has a meniscus that helps distribute body weight. Bursae are fluid-filled sacs found in certain synovial joints. They are usually located between the skin and the underlying body part. Bursae cushion and aid the movement of tendons that glide over bondy parts or other tendons.