The cranial bones are connected by fibrous joints called sutures. The neurocranium consists of the frontal, the ethmoid, the sphenoid, the occipital, and the paired temporal and parietal bones. Similarly, in the leg, the shafts of the tibia and fibula are also united by an interosseous membrane.The human skull consists of approximately 30 bones, which can be anatomically divided into the cranial bones ( neurocranium) and the facial bones ( viscerocranium). In the forearm, the wide gap between the shaft portions of the radius and ulna bones are strongly united by an interosseous membrane (see Figure 1b). The gap between the bones may be narrow, with the bones joined by ligaments, or the gap may be wide and filled in by a broad sheet of connective tissue called an interosseous membrane. Late in life, the sagittal, coronal, and lambdoid sutures of the skull will begin to ossify and fuse, causing the suture line to gradually disappear.Ī syndesmosis (“fastened with a band”) is a type of fibrous joint in which two parallel bones are united to each other by fibrous connective tissue. At the time of birth, the frontal and maxillary bones consist of right and left halves joined together by sutures, which disappear by the eighth year as the halves fuse together to form a single bone. Examples of synostosis fusions between cranial bones are found both early and late in life. This fusion between bones is called a synostosis (“joined by bone”). At some sutures, the connective tissue will ossify and be converted into bone, causing the adjacent bones to fuse to each other. When the connective tissue between the adjacent bones is reduced to a narrow layer, these fibrous joints are now called sutures. The fontanelles greatly decrease in width during the first year after birth as the skull bones enlarge. After birth, these expanded regions of connective tissue allow for rapid growth of the skull and enlargement of the brain. These broad areas of connective tissue are called fontanelles (Figure 2).ĭuring birth, the fontanelles provide flexibility to the skull, allowing the bones to push closer together or to overlap slightly, thus aiding movement of the infant’s head through the birth canal. In newborns and infants, the areas of connective tissue between the bones are much wider, especially in those areas on the top and sides of the skull that will become the sagittal, coronal, squamous, and lambdoid sutures. The fontanelles of a newborn’s skull are broad areas of fibrous connective tissue that form fibrous joints between the bones of the skull. (See Figure 1a.) Thus, skull sutures are functionally classified as a synarthrosis, although some sutures may allow for slight movements between the cranial bones. The suture is frequently convoluted, forming a tight union that prevents most movement between the bones. In adults, the skull bones are closely opposed and fibrous connective tissue fills the narrow gap between the bones. The fibrous connective tissue found at a suture (“to bind or sew”) strongly unites the adjacent skull bones and thus helps to protect the brain and form the face. (c) A gomphosis is a specialized fibrous joint that anchors a tooth to its socket in the jaw.Īll the bones of the skull, except for the mandible, are joined to each other by a fibrous joint called a suture. (b) An interosseous membrane forms a syndesmosis between the radius and ulna bones of the forearm. (a) Sutures join most bones of the skull. Fibrous joints form strong connections between bones. Lastly, a gomphosis is the narrow fibrous joint between the roots of a tooth and the bony socket in the jaw into which the tooth fits. This type of fibrous joint is found between the shaft regions of the long bones in the forearm and in the leg. At a syndesmosis joint, the bones are more widely separated but are held together by a narrow band of fibrous connective tissue called a ligament or a wide sheet of connective tissue called an interosseous membrane. A suture is the narrow fibrous joint found between most bones of the skull. The gap between the bones may be narrow or wide. Give an example of each type of fibrous jointĪt a fibrous joint, the adjacent bones are directly connected to each other by fibrous connective tissue, and thus the bones do not have a joint cavity between them (Figure 1).Distinguish between a suture, syndesmosis, and gomphosis.Describe the structural features of fibrous joints.
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