Cuantos huesos tiene la columna vertebral yahoo dating
The dorsal vertebrae range from the bottom of the neck to the top of the pelvis. Kyphosis is an exaggerated kyphotic concave curvature in the thoracic region, also called hyperkyphosis. Dorsal vertebrae attached to the ribs are called thoracic vertebrae, while those without ribs are called lumbar vertebrae. Amphicoelous vertebra have centra with both ends concave. Sometimes the spinal meninges and also the spinal cord can protrude through this, and this is called Spina bifida cystica.
When multiple sacral vertebrae are fused into a single structure, it is called the sacrum. Sometimes all of the vertebral arches may remain incomplete. Pain at the coccyx tailbone is known as coccydynia. Even these patterns are only generalisations, however, and there may be variation in form of the vertebrae along the length of the spine even within a single species.
Cervical vertebrae are those in the neck area. In the tail, these are attached to chevron-shaped bones called haemal arches, which attach below the base of the spine, and help to support the musculature. Centra with flat ends are acoelous, like those in mammals.
Procoelous vertebrae are anteriorly concave and posteriorly convex. Hagfishes lack a true vertebral column, and are therefore not properly considered vertebrates, but a few tiny neural arches are present in the tail. Caudal vertebrae compose the tail, and the final few can be fused into the pygostyle in birds, or into the coccygeal or tail bone in chimpanzees and humans. The thoracic vertebrae are partially fused, providing a solid brace for the wings during flight. Both of these structures are embedded within a single cylindrical mass of cartilage.
The shape of the vertebral body does, however, vary somewhat between different groups. The centrum of the vertebra can be classified based on the fusion of its elements.
Heterocoelous vertebrae have saddle -shaped articular surfaces. Where the condition does not involve this protrusion it is known as Spina bifida occulta. The presence of three or more sacral vertebrae, in association with the hip bones, is one of the defining characteristics of dinosaurs. They are found in salamanders, and in some non-avian dinosaurs. Fused elements, however, classify a vertebra as having holospondyly.
The synsacrum is a similar fused structure found in birds that is composed of the sacral, lumbar, and some of the thoracic and caudal vertebra, as well as the pelvic girdle. It is more common among females and may result from unequal growth of the two sides of one or more vertebrae, so that they do not fuse properly. These flat ends of the centra are especially good at supporting and distributing compressive forces. The vertebral processes can either give the structure rigidity, help them articulate with ribs, or serve as muscle attachment points.
The sacral vertebrae are those in the pelvic region, and range from one in amphibians, to two in most birds and modern reptiles, or up to three to five in mammals. There are generally three to five vertebrae with the sacrum, and anything up to fifty caudal vertebrae. The lower tube surrounds the notochord, and has a complex structure, often including multiple layers of calcification. Common types are transverse process, diapophyses, parapophyses, and zygapophyses both the cranial zygapophyses and the caudal zygapophyses. The occipital condyle is a structure on the posterior part of a dinosaur's skull which articulates with the first cervical vertebra.
In many hadrosaur and theropod dinosaurs, the caudal vertebrae were reinforced by ossified tendons. Spinal stenosis is a narrowing of the spinal canal which can occur in any region of the spine though less commonly in the thoracic region. The vertebral arch surrounds the spinal cord, and is of broadly similar form to that found in most other vertebrates. Amphicoelous centra often are integrated with a full notochord. Temporary lordosis is common during pregnancy.
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