The Ball-and-Socket Joint
January 10, 2011
Dr. Mike Liang
THE BALL-AND-SOCKET JOINT 2 The Ball-and-Socket Joint
Joints are essential in allowing movement of the human body. They are located at the intersection of bones, and their structures determine the type of movement that will occur at that location. Each joint contains components of the skeletal and muscular systems and connective tissues that function together to allow movement to occur. A ball-and-socket joint is one example of a synovial joint. In a ball-and-socket joint, the round head of one bone rests within a cup-shaped depression in another bone (Martini and Bartholomew, 2010). This joint is found in the shoulder and hip of the body, and allows the arm and leg to move in a 360 degree angle. This paper will closely examine the ball-and-socket joint in relations to the components from the skeletal system, muscular system, and connective tissues that enable the joint to function. The Skeletal System
The skeletal system contains 206 bones organized into an internal framework called the endoskeleton. The main functions of the skeletal system are to provide support for muscle and organs, give shape and structure to the body, and to protect soft tissues and organs. Bones in the skeleton also store minerals and energy reserves and manufacture blood cells (Martini & Barthelomew, 2010). The skeleton is composed of two main parts: the axial skeleton, which consists of 80 bones such as the ribs, spine, and cranium, and the appendicular skeleton, made up of 126 bones, such as the arms, legs, pelvis, and shoulder (Patts, 2001). Bones contain a tough outer membrane called a periosteum. This membrane is made up of a network of blood vessels that supply bone cells with oxygen and nutrients and remove carbon dioxide. Under the periosteum is compact bone. Compact bone is a hard material composed of mineral crystals and protein fibers. Inside the compact bone is a network of connective tissues called spongy bone. Bone marrow is soft tissue found in the centers and ends of long bones where blood cells are produced. Bones contain both red and yellow marrow. Red marrow is made of blood vessels, THE BALL-AND-SOCKET JOINT 3 fibers, and cells that manufacture erythrocytes and white blood cells. Yellow marrow consists mostly of fat cells that serve as energy (Farabee, 2001). Besides bones, the skeletal system is made up of cartilages, joints, ligaments, and other connective tissue that stabilizes or connects them. The place where two bones meet is a called a joint. Joints hold bones together and allow the skeleton to move. Joints also contain cartilage, to protect the surface of the bone; ligaments to stabilize the joint; tendons to connect the muscle to bone, and bursa, which are fluid-filled sacs found between ligaments and bone that help to decrease friction. Joints contain synovial fluid that lubricates them. Synovial fluid helps to protect a joint and it allows for stress-free movement. The most mobile joint in the body is the ball-and-socket joint. Ball-and-socket joints move in three planes and produce movements such as flexion, extension, internal and external rotation, abduction, adduction, and circumduction. Examples of ball-and-socket joints are found in the hip and shoulders. “Also called spheroidal joints, the ball and socket joints are formed by the rounded or "ball-shaped" head of one bone fitting into the cup-like cavity of another bone. The articulating bone fits into the cavity and allows the distal bone to move around” (Enotes Inc., 2011). The Muscular System
Approximately 600 muscles are in the human body. Muscle contains three types’ of tissue; skeletal muscle, cardiac muscle,...