Bursae reduce friction by separating the adjacent structures, preventing them from rubbing directly against each other. A tendon sheath is similar in structure to a bursa, but smaller.
It is a connective tissue sac that surrounds a muscle tendon at places where the tendon crosses a joint. It contains a lubricating fluid that allows for smooth motions of the tendon during muscle contraction and joint movements. Synovial joints are subdivided based on the shapes of the articulating surfaces of the bones that form each joint. The six types of synovial joints are pivot, hinge, condyloid, saddle, plane, and ball-and socket-joints Figure 6.
At a pivot joint , a rounded portion of a bone is enclosed within a ring formed partially by the articulation with another bone and partially by a ligament see Figure 6. The bone rotates within this ring. Since the rotation is around a single axis, pivot joints are functionally classified as a uniaxial diarthrosis type of joint. An example of a pivot joint is the atlantoaxial joint, found between the C1 atlas and C2 axis vertebrae.
Here, the upward projecting dens of the axis articulates with the inner aspect of the atlas, where it is held in place by a ligament. Rotation at this joint allows you to turn your head from side to side. A second pivot joint is found at the proximal radioulnar joint. Here, the head of the radius is largely encircled by a ligament that holds it in place as it articulates with the radial notch of the ulna. Rotation of the radius allows for forearm movements. In a hinge joint , the convex end of one bone articulates with the concave end of the adjoining bone see Figure 6.
This type of joint allows only for bending and straightening motions along a single axis, and thus hinge joints are functionally classified as uniaxial joints. A good example is the elbow joint, with the articulation between the trochlea of the humerus and the trochlear notch of the ulna. Other hinge joints of the body include the knee, ankle, and interphalangeal joints between the phalanx bones of the fingers and toes.
At a condyloid joint ellipsoid joint , the shallow depression at the end of one bone articulates with a rounded structure from an adjacent bone or bones see Figure 6. The knuckle metacarpophalangeal joints of the hand between the distal end of a metacarpal bone and the proximal phalanx bone are condyloid joints.
Another example is the radiocarpal joint of the wrist, between the shallow depression at the distal end of the radius bone and the rounded scaphoid, lunate, and triquetrum carpal bones. In this case, the articulation area has a more oval elliptical shape.
Functionally, condyloid joints are biaxial joints that allow for two planes of movement. One movement involves the bending and straightening of the fingers or the anterior-posterior movements of the hand. The second movement is a side-to-side movement, which allows you to spread your fingers apart and bring them together, or to move your hand in a medial-going or lateral-going direction.
At a saddle joint , both of the articulating surfaces for the bones have a saddle shape, which is concave in one direction and convex in the other see Figure 6. This allows the two bones to fit together like a rider sitting on a saddle.
Saddle joints are functionally classified as biaxial joints. The primary example is the first carpometacarpal joint, between the trapezium a carpal bone and the first metacarpal bone at the base of the thumb.
This joint provides the thumb the ability to move away from the palm of the hand along two planes. Thus, the thumb can move within the same plane as the palm of the hand, or it can jut out anteriorly, perpendicular to the palm. The sternoclavicular joint is also classified as a saddle joint. At a plane joint gliding joint , the articulating surfaces of the bones are flat or slightly curved and of approximately the same size, which allows the bones to slide against each other see Figure 6.
The motion at this type of joint is usually small and tightly constrained by surrounding ligaments. Based only on their shape, plane joints can allow multiple movements, including rotation. Thus plane joints can be functionally classified as a multiaxial joint. However, not all of these movements are available to every plane joint due to limitations placed on it by ligaments or neighboring bones.
Thus, depending upon the specific joint of the body, a plane joint may exhibit only a single type of movement or several movements. Plane joints are found between the carpal bones intercarpal joints of the wrist or tarsal bones intertarsal joints of the foot, between the clavicle and acromion of the scapula acromioclavicular joint , and between the superior and inferior articular processes of adjacent vertebrae zygapophysial joints.
The joint with the greatest range of motion is the ball-and-socket joint. At these joints, the rounded head of one bone the ball fits into the concave articulation the socket of the adjacent bone see Figure 6. The hip joint and the glenohumeral shoulder joint are the only ball-and-socket joints of the body.
At the hip joint, the head of the femur articulates with the acetabulum of the hip bone, and at the shoulder joint, the head of the humerus articulates with the glenoid cavity of the scapula. Ball-and-socket joints are classified functionally as multiaxial joints.
The femur and the humerus are able to move in both anterior-posterior and medial-lateral directions and they can also rotate around their long axis. The shallow socket formed by the glenoid cavity allows the shoulder joint an extensive range of motion. In contrast, the deep socket of the acetabulum and the strong supporting ligaments of the hip joint serve to constrain movements of the femur, reflecting the need for stability and weight-bearing ability at the hip.
Watch this video to see an animation of synovial joints in action. Synovial joints are places where bones articulate with each other inside of a joint cavity. The different types of synovial joints are the ball-and-socket joint shoulder joint , hinge joint knee , pivot joint atlantoaxial joint, between C1 and C2 vertebrae of the neck , condyloid joint radiocarpal joint of the wrist , saddle joint first carpometacarpal joint, between the trapezium carpal bone and the first metacarpal bone, at the base of the thumb , and plane joint facet joints of vertebral column, between superior and inferior articular processes.
Which type of synovial joint allows for the widest range of motion? Arthritis is a common disorder of synovial joints that involves inflammation of the joint. This often results in significant joint pain, along with swelling, stiffness, and reduced joint mobility. There are more than different forms of arthritis. Arthritis may arise from aging, damage to the articular cartilage, autoimmune diseases, bacterial or viral infections, or unknown probably genetic causes. Risk factors that may lead to osteoarthritis later in life include injury to a joint; jobs that involve physical labor; sports with running, twisting, or throwing actions; and being overweight.
These factors put stress on the articular cartilage that covers the surfaces of bones at synovial joints, causing the cartilage to gradually become thinner. As the articular cartilage layer wears down, more pressure is placed on the bones.
The joint responds by increasing production of the lubricating synovial fluid, but this can lead to swelling of the joint cavity, causing pain and joint stiffness as the articular capsule is stretched. The bone tissue underlying the damaged articular cartilage also responds by thickening, producing irregularities and causing the articulating surface of the bone to become rough or bumpy. Joint movement then results in pain and inflammation.
As with all synovial joints, each bony surface is covered by a layer of smooth articular cartilage. The space between the cartilages is filled with lubricating synovial fluid. The fluid is contained within a fibrous joint capsule, which permits movement.
The fibrous joints formed by the disks permit only a little movement between the regular cervical vertebrae. In the intervals between the occiput, the atlas, and the axis, where so much movement occurs there are no disks, only synovial joints.
Avatar icon Avatar icon Sign In. Already a Subscriber? Required Required. Forgot Password? A multiaxial joint, such as the shoulder or hip joint, allows for three planes of motions. The joint between adjacent vertebrae that includes an invertebral disc is classified as which type of joint?
Define how joints are classified based on function. Describe and give an example for each functional type of joint. Functional classification of joints is based on the degree of mobility exhibited by the joint. A synarthrosis is an immobile or nearly immobile joint. An example is the manubriosternal joint or the joints between the skull bones surrounding the brain.
An amphiarthrosis is a slightly moveable joint, such as the pubic symphysis or an intervertebral cartilaginous joint. A diarthrosis is a freely moveable joint. These are subdivided into three categories. A uniaxial diarthrosis allows movement within a single anatomical plane or axis of motion. The elbow joint is an example. A biaxial diarthrosis, such as the metacarpophalangeal joint, allows for movement along two planes or axes. The hip and shoulder joints are examples of a multiaxial diarthrosis.
These allow movements along three planes or axes. The functional needs of joints vary and thus joints differ in their degree of mobility. A synarthrosis, which is an immobile joint, serves to strongly connect bones thus protecting internal organs such as the heart or brain.
A slightly moveable amphiarthrosis provides for small movements, which in the vertebral column can add together to yield a much larger overall movement. The freedom of movement provided by a diarthrosis can allow for large movements, such as is seen with most joints of the limbs. Skip to content Joints. Learning Objectives By the end of this section, you will be able to: Distinguish between the functional and structural classifications for joints Describe the three functional types of joints and give an example of each List the three types of diarthrodial joints.
Structural Classification of Joints The structural classification of joints is based on whether the articulating surfaces of the adjacent bones are directly connected by fibrous connective tissue or cartilage, or whether the articulating surfaces contact each other within a fluid-filled joint cavity.
Functional Classification of Joints The functional classification of joints is determined by the amount of mobility found between the adjacent bones. Synarthrosis An immobile or nearly immobile joint is called a synarthrosis. Suture Joints of Skull. The suture joints of the skull are an example of a synarthrosis, an immobile or essentially immobile joint. Intervertebral Disc. An intervertebral disc unites the bodies of adjacent vertebrae within the vertebral column.
Each disc allows for limited movement between the vertebrae and thus functionally forms an amphiarthrosis type of joint. Intervertebral discs are made of fibrocartilage and thereby structurally form a symphysis type of cartilaginous joint.
Multiaxial Joint. A multiaxial joint, such as the hip joint, allows for three types of movement: anterior-posterior, medial-lateral, and rotational. Review Questions The joint between adjacent vertebrae that includes an invertebral disc is classified as which type of joint? Which of these joints is classified as a synarthrosis?
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