Navigation Links
Joint


This article is about a joint in zootomical anatomy. For other meanings of the word "joint", see Joint (disambiguation).


A joint is the location at which two bones make contact. Structurally, the joints are classified as:

  • fibrous - bones are connected by fibrous connective tissue.
  • cartilaginous - bones are connected by cartilage.
  • synovial - there is a space (synovial cavity) between the articulating bones.

Functionally, they can be classified as:

  • synarthrosis - permit no movement.
  • amphiarthrosis - permit little movement.
  • diarthrosis - permit a variety of movements (e.g. flexion , adduction, pronation). Only synovial joints are diarthrosis.


Contents

Synarthrosis joints

Synarthroses are joints with very little (if any) mobility. They can can be categorised by how the two bones are joined together:

  • Syndesmoses are joints where the two bones are joined by one of more ligaments.
  • Synchondroses are joints where the two bones are joined by a piece of cartilage.
  • Synostoses are the fusion of two bones, to the point that they are practically one bone. In humans, the plates of the cranium, initially separate, fuse together as the child approaches adulthood. Children whose craniums fuse too early may suffer deformities and brain damage, as the skull does not expand properly to accommodate the growing brain - a condition known as craniostenosis.
  • Amphiarthroses are slightly moveable joints where the two bone surfaces at the joint - both covered in hyalin cartilage - are joined by strands of fibrocartilage.

Diarthrosis joints

Diarthroses (sometimes called synovial joints) are the most common and most moveable type of joint in the body.

The whole of a diarthrosis is contained by a ligamentous sac called the articluar capsule.

The surfaces of the two bones at the joint are covered in cartilage. The thickness of the cartilage varies with each joint, and sometimes may be of uneven thickness. Articular cartilage is multi-layered. A thin superficial layer provide a smooth surface for the two bones to slide against each other. Of all the layers, it has a the highest concentration of collagen and the lowest concentration of proteoglycans , making it very resistant to shear stresses. Deeper than that is an intermediate layer, which is mechanically designed to absorb shocks and distribute the load efficiently. The deepest layer is highly calcified, and anchors the articular cartilage to the bone.

In joints where the two surfaces do not fit snugly together, a meniscus or multiple folds of fibro-cartilage within the joint correct the fit, ensuring stability and the optimal distribution of load forces.

The synovium is a membrane that covers all the non-cartilaginous surfaces within the articular capsule. It secretes synovial fluid into the joint, which nourishes and lubricates the articular cartilage. The synovium is separated from the capsule by a layer of celluar tissue that contains blood vessels and nerves.

Synovial joints can be further grouped by their shape, which controls the movement they allow:

  • Gliding joints, such as in the carpals of the wrist. These joints allow a wide variety of movement, but not much distance.
  • Hinge joints, such as the elbow (between the humerus and the ulna). These joints act like a door hinge, allowing flexion and extension in just one plane.
  • Pivot joints, such as the elbow (between the radius and the ulna). This is where one bone rotates about another.
  • Condyloid (ellipsoid) joints, such as the knee. When the knee is extended there is no rotation, when it is flexed some rotation is possible. A condyloid joint is where two bones fit together with an odd shape (e.g. an ellipse), and one bone is concave, the other convex. Some classifications make a distinction between condyloid and ellipsoid joints.
  • Saddle joints, such as at the thumb (between the metacarpal and carpal). Saddle joints, which resemble a saddle, permit the same movements as the condyloid joints.
  • Ball and socket joints, such as the hip joint. These allow a wide arrange of movement.

Cartilaginous joints

In cartilaginous joints (also known as synchondroses) bones are connected entirely by cartilage. In comparison to synovial joints, cartilaginous joints allow only slight movement. Examples of cartilaginous joints are the pubic symphysis, the joints between the ribs and the sternum, and the cartilage connecting the growth regions of immature long bones.

Fibrous joints

In fibrous joints bones are joined by tight and inflexible layers of dense connective tissue, consisting mainly of collagen fibers. In adults, these are not designed to allow any movement; however, in children, fibrous joints have not solidified and are movable. Examples of fibrous joints are:

  • Cranial sutures, joining the bones of the cranium.
  • Gomphoses, the joints between the roots of the teeth and their sockets (or alveoli) in maxilla and mandible.

See also: condyloprotector , arthritis.


'"/>


(Date:7/25/2014)... colonial era, 100,000s of people lived on the land ... fire to control the availability of plants they used ... to use fire to maintain desired habitat and natural ... Forest Service,s Pacific Southwest Station, will lead a ... Refuge during the Ecological Society of America,s 99th Annual ...
(Date:7/25/2014)... raging this summer and some of the smoke from those ... image collected by the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard ... smoke has descended over the Great Lakes region of the ... image from July 23, 2014 (first image feature highlighted below) ... off southeastward. In the image, it is over Manitoba ...
(Date:7/25/2014)... online in the International Journal of Cancer ... cervical cancer based on findings showing successful reduction in ... discrete population of cells in the cervix. , ... squamocolumnar junction cells, or SCJ cells. These cells reside ... the origins of cervical cancer. A research team co-led ...
Breaking Biology News(10 mins):Fire ecology manipulation by California native cultures 2Fire ecology manipulation by California native cultures 3Clearing cells to prevent cervical cancer 2
... FARMINGTON, Conn., April 23, 2012 /PRNewswire-iReach/  -- Global ... Early Bird discounted registration for three important Boston healthcare ... Pioneers from across the rapidly maturing kinase ... of what lies ahead at the Next-Gen Kinase ...
... annual losses of millions of dollars and pose serious challenges ... difficult and expensive. According to T. D. Schowalter, author ... Integrated Pest Management called " Ecology and Management of ... ) in Southern Pine Forests ," preventative measures are most ...
... Biology 2012, Dr. Blake Rasmussen and colleagues presented a ... vs. Whey Protein Ingestion on Muscle Protein Synthesis Following ... that a protein blend (combination of soy, whey and ... muscle. Specifically, the blend of proteins in this study ...
Cached Biology News:Attendees Save Up To $800 on Boston-area Pharmaceutical and Healthcare Conferences, Early Bird Discounts Expiring April 27 2Attendees Save Up To $800 on Boston-area Pharmaceutical and Healthcare Conferences, Early Bird Discounts Expiring April 27 3New study finds a protein combination is best to consume post-workout for building muscle 2
Other biology definitionOther Tags