Introduction[edit | edit source] Show
The three joints in the body (Histologically) are fibrous, cartilaginous, and synovial. Synovial joints are the most common type of joint in the body (see image 1). These joints are termed diarthroses, meaning they are freely mobile.[1] A key structural characteristic for a synovial joint that is not seen at fibrous or cartilaginous joints is the presence of a joint cavity. The joint cavity contains synovial fluid, secreted by the synovial membrane (synovium), which lines the articular capsule. This fluid-filled space is the site at which the articulating surfaces of the bones contact each other. Hyaline cartilage forms the articular cartilage, covering the entire articulating surface of each bone. The articular cartilage and the synovial membrane are continuous. A few synovial joints of the body have a fibrocartilage structure located between the articulating bones. This is called an articular disc, which is generally small and oval-shaped, or a meniscus, which is larger and C-shaped.[2][3]. Synovial joints are often further classified by the type of movements they permit. There are six such classifications: hinge (elbow), saddle (carpometacarpal joint), planar (acromioclavicular joint), pivot (atlantoaxial joint), condyloid (metacarpophalangeal joint), and ball and socket (hip joint).[2] Features of all Synovial Joints[edit | edit source]
Additional features within some Synovial Joints[edit | edit source]
Image 2: Knee joint. In a Synovial joint, the ends of bones are encased in smooth cartilage. Together, they are protected by a joint capsule lined with a synovial membrane that produces synovial fluid. The capsule and fluid protect the cartilage, muscles, and connective tissues. [4] Additional features surrounding some Synovial Joints[edit | edit source]
Additional Support[edit | edit source]At many synovial joints, additional support is provided by the muscles and their tendons that act across the joint.
Types of Synovial Joints[edit | edit source]Image 4: Types of Synovial Joints: The six types of synovial joints allow the body to move in a variety of ways. (a) Pivot joints allow for rotation around an axis, such as between the first and second cervical vertebrae, which allows for side-to-side rotation of the head. (b) The hinge joint of the elbow works like a door hinge. (c) The articulation between the trapezium carpal bone and the first metacarpal bone at the base of the thumb is a saddle joint. (d) Plane joints, such as those between the tarsal bones of the foot, allow for limited gliding movements between bones. (e) The radiocarpal joint of the wrist is a condyloid joint. (f) The hip and shoulder joints are the only ball-and-socket joints of the body. The six types of synovial joints are:
Nerve Supply[edit | edit source]Sensory and autonomic fibers innervate synovial joints:
Two general principles apply to synovial joint innervation:
Blood Supply[edit | edit source]Synovial joints receive vascular supply through a rich anastomosis of arteries extending from either side of the joint ie the periarticular plexus. Some vessels penetrate the fibrous capsule to form a rich plexus deeper in the synovial membrane. The articular cartilage, which is avascular hyaline cartilage, is nourished by the synovial fluid. Lymphatic vessels for every joint follow the lymph drainage of the surrounding tissue—some joints house lymph nodes, like the popliteal lymph nodes in the popliteal fossa of the knee[1]. [edit | edit source]Typically seen in patients with osteoarthritis, rheumatoid arthritis, and other arthritic conditions. Joints contain sensory nerves called baro-receptors which respond to changes in atmospheric pressure. These receptors especially react when there is low barometric pressure, meaning the atmosphere has gone from dry to moist, like when it is going to rain. When pressure in the environment changes, we know that the amount of fluid in the joint or the pressure inside the joint fluctuates with it. Individuals with arthritic joints feel these changes much more because they have less cartilage to provide cushioning.[5] References[edit | edit source]
Which are parts of a joint capsule quizlet?a joint capsule or articular capsule is an envelope surrounding a synovial joint. Each joint capsule has two parts: an outer fibrous layer or membrane, and an inner synovial layer or membrane.
What fluid is in the joint capsule?Synovial fluid, also known as joint fluid, is a thick liquid located between your joints. The fluid cushions the ends of bones and reduces friction when you move your joints.
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