vertebral columns, also known as spine or spine , are part of the axial frame. The vertebral column is a defining characteristic of vertebrates, where the notochord (flexible rod of uniform composition) found in all chordates has been replaced by a series of segmented bones - the spine is separated by intervertebral discs. The vertebral column accommodates the spinal canal, the cavity that encloses and protects the spinal cord.
There are about 50,000 animal species that have vertebral columns. The human vertebral column is one of the most studied examples.
Video Vertebral column
Structure
In the human vertebral column there are usually thirty-three vertebrae; the twenty-four above articulate and separate from each other with intervertebral discs, and the lower nine converge in adults, five in the sacrum and four in the tail bone or the tail bone. Articulated vertebrae are named according to their spinal region. There are seven cervical vertebrae, twelve thoracic vertebrae and five lumbar vertebrae. The number of vertebrae in a region may vary but the overall number remains the same. Their numbers are in the cervical area but rarely change.
There are ligaments that extend the length of the columns in front and back, and between the vertebrae joining the spinous processes, the transverse processes and the vertebral lamina.
Vertebra
The vertebrae of the human vertebral column is divided into different regions, which are related to the curve of the spine. Articulated vertebrae are named according to their spinal region. The vertebrae in this region are essentially the same, with little variation. These areas are called the cervical spine, the thoracic spine, the lumbar spine, the sacrum and the coccyx. There are seven cervical vertebrae, twelve thoracic vertebrae and five lumbar vertebrae. The number of vertebrae in a region may vary but the overall number remains the same. Their numbers are in the cervical area but rarely change. The cervical vertebral vertebrae, thorax and lumbar are independent bones, and are generally quite similar. The vertebrae of sacrum and coccyx are usually fused and can not move independently. Two special vertebra are the atlas and the axis, where the head rests.
The typical vertebra consists of two parts: the vertebral body and the vertebral arch. The vertebral lump is posterior, which means the back face of a person. Together, these attach the vertebral foramen, which contains the spinal cord. Because the spinal cord ends up in the lumbar spine, and the sacrum and tail bones are fused, they do not contain central foramen. The vertebral lump is formed by a pair of pedicles and a pair of lamina, and supports seven processes, four articular, two transverse, and one spinous, the latter also known as the spinal nerve. Two transverse processes and one spinous process are posterior to the (back) of the vertebral body. The spinous process comes out of the back, a process runs out from the left, and one on the right. The spinous processes of the cervical and lumbar regions can be felt through the skin.
Above and below each vertebra is a joint called the facet joint. This limits the range of possible movements, and joins the thin part of the neural arch called pars interarticularis . Among each pair of vertebrae are two small holes called intervertebral foramina. The spinal cord leaves the spinal cord through these holes.
The individual's vertebrae are named according to the region and position. From top to bottom, the vertebra is:
- Cervical spine: 7 vertebrae (C1-C7)
- Thoracic spine: 12 vertebrae (T1-T12)
- Lumbar spine: 5 vertebrae (L1-L5)
- Sacrum: 5 (united) vertebrae (S1-S5)
- Tail-bone: 4 (3-5) (fused) spine (tailbone)
Shape
The upper cervical spine has a forward, convex curve, which begins on the axis (the second cervical vertebra) at the top of the process or the odontoid nest, and ends in the middle of the second thoracic vertebra; it is the least marked of all indentations. This inner curve is known as the lordotic curve.
The thoracic curve, concave forward, begins in mid-second and ends in the middle of the twelfth thoracic vertebra. The most prominent point behind it relates to the spinous process of the seventh thoracic spine. This curve is known as the kyphotic curve.
The lumbar curve is more marked in women than in men; starting in the middle of the last thoracic spine, and ending at the sacrovertebral angle. Convex in the anterior portion, the convexity of the three lower vertebrae becomes much larger than the two above. This curve is described as a lordotic curve.
The sacrum curve begins at the sacrovertebral articulation, and ends at the coccyx point; the basin is directed downwards and forwards as a kyphotic curve.
The thoracal and sacralis kyphotic curves are called the primary curves, because they are present in the fetus. The cervical and lumbar curves are compensated or secondary , and developed after birth. The cervical curve is formed when the baby is able to lift his head (at three or four months) and to sit upright (at nine months). The lumbar curve is formed later from twelve to eighteen months, when the child begins to walk.
Surface
- The outer surface
When viewed from the front, the width of the vertebral body appears to increase from the second cervix to the first thorax; then there is a slight reduction in the next three vertebrae; below there is another gradual and progressive increase in width as low as sacrovertebral angle. From this point there is a rapid reduction, to the peak of coccyx.
- Posterior surface
From behind, the vertebral column appears in the median line of the spinous process. In the cervical area (with the exception of the second and seventh vertebrae) these are short, horizontal and bifid. At the top of the thoracic area they are directed downward sloping; in the center they are almost vertical, and at the bottom they are almost horizontal. In the lumbar area they are almost horizontal. The spinous process is separated by a considerable interval in the lumbar region, with a narrower interval around the neck, and is approached closely in the middle of the thoracic region. Sometimes one of these processes deviates slightly from the median line - which can sometimes be an indication of fracture or spinal displacement. On both sides of the spinous process is a vertebral groove formed by the lamina in the cervical and lumbar regions, where it is shallow, and by the lamina and transverse processes in the thoracic region, where it is deep and wide; these grooves put the inner muscles of the back. Lateral to the spinous process is an articular process, and still more lateral in the transverse process. In the thoracic region, the transverse process stays backward, on the far plane behind it from the same process in the cervical and lumbar regions. In the cervical area, the transverse process is placed in front of the articular, lateral process of the pedicles and between the intervertebral foramina. In thoracic regions they are posterior to the pedicles, intervertebral foramen, and articular processes. In the lumbar region they are in front of the articular process, but behind the intervertebral foramen.
- Lateral surface
The sides of the vertebral column are separated from the posterior surface by the articular processes in the cervical and thoracic regions, and by the transverse processes in the lumbar region. In the thoracic region, the sides of the vertebral body are marked behind by facets for articulation with the rib head. More posterior is the intervertebral forament, formed by the juxtaposition of the vertebral notches, the smallest oval in shape, the cervix and the upper part of the thoracic region, and gradually increasing in size to the last lumbar. They transmit specialized spinal nerves and lie between the transverse processes in the cervical region, and in front of them in the thoracic and lumbar regions.
Ligaments
There are different ligaments involved in holding together from the spine in the column, and in the movement of the column. The anterior and posterior longitudinal ligaments extend the length of the vertebral column along the front and back of the vertebral body. Interspinous ligaments connect the spinous processes adjacent to the vertebrae. Supraspinous ligaments extend the length of the spine that runs along the back of the spinous process, from the sacrum to the seventh cervical vertebra. From there it continues with nuchal ligaments.
Development
A prominent spine segmented pattern is formed during embryogenesis when somit is rhythmically added to the posterior embryo. The formation of the Somite begins around the third week when the embryo begins to gastrulate and continues until about 52 somites are formed. Somit is a sphere, formed from the paraxial mesoderm located on the side of the neural tube and contains the precursors of the spinal bone, the ribs of the vertebra and several skulls, as well as the muscles, ligaments and skin. Somitogenesis and subsequent distributions are controlled by the clock and wavefront models acting in paraxial mesoderm cells. Immediately after their formation, sclerotomes, which give rise to some skull, spinal and rib bones, migrate, leaving the rest of somite which is now called dermamyotome behind. It then breaks out to give myotomes which will form the muscles and dermatomes that will form the skin of the back. The sclerotom becomes divided into anterior and posterior compartments. This subdivision plays a key role in the definitive pattern of the vertebra that forms when the posterior part of a second somit to the anterior part of the somit sequence during a process called resegmentation. The disruption of the process of somitogenesis in humans results in diseases such as congenital scoliosis. So far, the human homologues of the three genes associated with the mouse segmentation clock, (MESP2, DLL3 and LFNG), have been shown to mutate in cases of congenital scoliosis, suggesting that the mechanisms involved in vertebral segmentation are preserved across vertebrates. In humans the first four are joined at the base of the occipital bone of the skull and the next 33 somes will form the spine, ribs, muscles, ligaments and skin. Posterior left posterior poses. During the fourth week of embryogenesis, sclerotomes shift their position to surrounding the spinal cord and notochord. These network columns have a segmented appearance, with solid back and forth areas and less dense areas.
As the sclerotome develops, it further condenses eventually evolves into the vertebral body. The development of the exact shape of the vertebral body is governed by the HOX gene .
The less dense tissue that separates the sclerotome segments develops into intervertebral discs.
The notochord disappears in the sclerotome segment (vertebral body), but remains in the intervertebral disc region as the nucleus pulposus. The nucleus pulposus and fibers of the annulus fibrosus form the intervertebral disc.
The primary curve (thoracic and sacral arch) is formed during the development of the fetus. The secondary curve develops after birth. The cervical curvature forms as a result of the raised head and lumbar form of curvature as a result of walking.
Maps Vertebral column
Function
Spinal cord
The vertebral column surrounds the spinal cord that runs inside the spinal canal, formed from the central hole within each vertebra. The spinal cord is part of the central nervous system that supplies the nerves and receives information from the peripheral nervous system in the body. The spinal cord consists of gray and white matter and central cavity, the central canal. Adjacent to each spinal cord appears spinal. The spinal cord provides the supply of sympathetic nerves to the body, with nerves emerging to form sympathetic stems and splanknik nerves.
The spinal canal follows a different curve from the column; it's large and triangular in parts of the column that enjoys the greatest freedom of movement, such as the cervical and lumbar regions; and small and round in the thoracic region, where movement is more limited.
The spinal cord ends up in the conus medullaris and cauda equina.
Clinical interests
Disease
Spina bifida is a congenital aberration in which there is a broken vertebral arch ligation closure. Sometimes the spine meninges and also the spinal cord can extend through this, and this is called Spina bifida cystica . Where the condition does not involve this bulge is known as Spina bifida occulta. Sometimes all vertebral arches may remain incomplete. Another, though rare, congenital disease is the Klippel-Feil syndrome which is a combination of two of the cervical vertebrae.
Spondylolisthesis is a forward shift of the vertebra and retrolistesis is the posterior displacement of one vertebral body with respect to the adjacent vertebra to a level less than dislocation.
Spinal disc hernias, more commonly called "skipping disks," are the result of a tear in the outer ring (annulus fibrosus) of the intervertebral disc, allowing some substance such as a soft gel, nucleus pulposus, protruding out of the hernia.
Spinal stenosis is a narrowing of the spinal canal that can occur in every spinal region although it is less common in the thoracic region. Stenosis can constrict the spinal canal causing neurological deficits.
Pain in coccyx (coccyx) is known as coccydynia.
Spinal cord injury is damage to the spinal cord that causes changes in function, either temporarily or permanently.
Curvature
Excessive or abnormal spinal curvature is classified as a spinal or dorsopathic disease and includes the following abnormal curvature:
- Kyphosis is an excessive kyphotic curvature in the thoracic region, also called hyperkyphosis. This results in what is called a "humpback" or "dowager's hump", a condition commonly produced from osteoporosis.
- Lordosis as an exaggerated lordotic curvature in the lumbar region, known as lumbar hyperlordosis and also as a "swayback". Temporary lordosis is common during pregnancy.
- Scoliosis, lateral curvature, is the most common abnormal curvature, occurring in 0.5% of the population. This is more common among women and may result from unequal growth of two sides of one or more vertebrae, so they do not blend in properly. This can also be caused by pulmonary atelectasis (partial or complete deflection of one or more lobe lobes) as observed in asthma or pneumothorax.
- Kyphoscoliosis, a combination of kyphosis and scoliosis.
Historic Buildings
The individual vertebrae of the human vertebral columns can be felt and used as anatomical surfaces, with reference points drawn from the middle of the vertebral body. It provides anatomical landmarks that can be used to guide procedures such as lumbar puncture and also as a vertical reference point to describe the location of other parts of human anatomy, such as the position of organs.
Other animals
Variations in vertebra
The general structure of vertebra in other animals is mostly the same as in humans. The individual vertebra consists of the centrum, the protruding arches of the upper and lower parts of the centrum, and the various processes projected from the centrum and/or arch. An elongated arch from the top of the centrum is called the nerve arch, while the haemal or chevron arch is found below the centrum in the fish tail vertebra, mostly reptiles, some birds, some dinosaurs and some long-tailed mammals. Vertebral processes can provide structural stiffness, help them articulate with ribs, or serve as a point of muscle attachment. Common types are transversus processes, diapophyses, parapophyses, and zygapophyses (both cranial zigapophyses and caudal zygapophyses). Sentrum vertebra can be classified based on the combination of its elements. In temnospondyls, bone like spinous processes, pleurocentrum and intercentrum are separate ossification. The fused element, however, classifies the vertebra as having holospondyly.
A vertebra can also be described in the form of centrum ends. Centra with flat tip is acoelous , as it is in mammals. The flat edges of the center are excellent for supporting and distributing compressive strength. Amphicoelous The vertebra has a centra with both concave ends. This form is common in fish, where most of the movement is limited. Centra amphascus is often integrated with a full notochord. Procoelous The vertebra is the anterior concave and the posterior convex. They are found in modern frogs and reptiles. Opisthocoelous The vertebra is the opposite, having an anterior convexity and posterior concave. They are found in salamanders, and in some non-avian dinosaurs. Heterocoelous The vertebra has a syrupy articular surface. This type of configuration is seen in turtles pulling back their necks and birds, as it allows extensive vertical and lateral flexion movement without stretching too wide a nerve strand or squeezing its long axis.
On horses, Arabs (breed) can have one fewer bones and a pair of ribs. This weirdness is lost to foals which are products of Arabian and other types of horses.
Regional vertebra
The vertebrae is defined by the region of the vertebral column that occurs, as in humans. The cervical vertebrae are those in the neck region. With the exception of two genera sloth ( choloepus and Bradypus ) and genus manatee, ( trichechus ), all mammals have seven cervical vertebrae. In other vertebrates, the number of cervical vertebrae can range from one vertebra in amphibians, up to 25 on a goose or 76 in the extinct plesiosaur Elasmosaurus . Dorsal vertebral range from the bottom of the neck to the top of the pelvis. The dorsal vertebrae attached to the rib is called the thoracic vertebrae, while the ribless spine is called the lumbar vertebrae. The sacrum vertebra are those in the pelvic region, and range from one in amphibians, two in most modern birds and reptiles, or up to three to five in mammals. When some sacred bones merge into one structure, this is called a sacrum. Synsacrum is a similar fused structure found in birds consisting of sacral, lumbar, and some thoracic and caudal vertebrae, as well as a pelvic girdle. The caudal vertebra forms a tail, and the latter may coalesce into pygostyle in birds, or to coccygeal bone or tail in chimpanzees (and humans).
Fish and amphibians
The lobe finned fish vertebra consists of three discrete bone elements. The vertebral artery surrounds the spinal cord, and has a shape similar to that found in other vertebrates. Just below the curvature lies a small pleurocentrum like a plate, which protects the top surface of the notochord, and beneath it, a larger arch-shaped curvature to protect the lower border. Both of these structures are embedded in a single cylindrical mass of cylinders. Similar arrangements are found in primitive Labyrinthodonts, but in the evolutionary line that causes reptiles (and hence, also for mammals and birds), the intercentrum becomes partially or completely replaced by an enlarged pleurocentrum, which in turn becomes the vertebral bone of the body. In most ray-finned fish, including all teleost, these two structures combine with, and are embedded within, a solid piece of bone that resembles the shallow bodies of the mammalian vertebral. In living amphibians, there is only a cylindrical piece under the vertebral arch, without traces of the separate elements present in the early tetrapods.
In cartilaginous fish, such as sharks, the spine consists of two cartilage tubes. The upper tube is formed from the vertebral arch, but also includes an additional cartilaginous structure filling the gap between the spine, and enclosing the spinal cord in its continuous casing. The lower tube surrounds the notochord, and has a complex structure, often including several layers of calcification.
Lamprey has a vertebral arch, but nothing resembles the vertebral body found in all higher vertebrates. Even the archs are intermittent, consisting of separate pieces of arch-shaped cartilage around the spinal cord in most of the body, transformed into long strips of cartilage above and below in the tail area. Hagfish has no actual vertebral column, and is therefore not considered vertebrates, but some small nerve arches are present in the tail.
Other vertebrates
The general structure of the human vertebra is quite common in mammals, reptiles, and birds. The vertebral body shape, however, is somewhat different between different groups. In mammals, like humans, it usually has an upper and lower flat surface, whereas in anterior reptiles the surface usually has a concave socket in which the convex face extended from the next vertebral body fits. Even these patterns are only generalizations, and there may be variations in the form of vertebrae along the length of the spine even in one species. Some unusual variations include saddle-shaped sockets between the cervical vertebra of birds and the presence of narrow hollow channels that flow in the middle of the gecko's and tuatara's vertebral bodies, containing the remainder of the notochord.
Reptiles often retain a primitive intercentra, which is present as a small crescent-shaped element located between adjacent vertebral bodies; Similar structures are often found in mammalian tail vertebrae. On the tail, it is attached to a chevron-shaped bone called the curve haemal , which is attached beneath the base of the spine, and helps to support the muscles. These last bones may be homologous with the fish's ribs. The number of vertebrae in the reptile spine varies greatly, and possibly several hundred in some species of snake.
In birds, there are a number of variables of cervical vertebrae, which often form the only highly flexible spinal part. The thoracic vertebrae is partly fused, providing a solid buffer for the wings during flight. The sacral vertebrae coalesce with the lumbar vertebrae, and some thoracic and caudal vertebrae, to form a single structure, synsacrum , which thus has a relatively greater length than the mammalian sacrum. In live birds, the remaining caudal vertebrae combine to become a further bone, pygostyle, for the fitting of the tail feathers.
Aside from the tail, the number of vertebrae in a mammal is generally fairly constant. Almost always there are seven cervical vertebrae (sloth and manate are some exceptions), followed by about twenty or more vertebrae, divided between the thoracic and lumbar forms, depending on the number of ribs. There are usually three to five vertebrae with sacrum, and anything up to fifty caudal vertebrae.
Dinosaur
The vertebral column of the dinosaur consists of the cervix (neck), back (back), sacral (hip), and tail vertebrae (tail). The Saurischian dinosaur vertebra sometimes has a feature known as pleurocoels, which is a hollowed hollow in the lateral part of the vertebrae, perforated to create an entrance to the air space inside the spine, which serves to reduce the weight of these bones without sacrificing strength. These pleurocoels are filled with an air sac, which will lose weight. In sauropod dinosaurs, land vertebrates, pleurocoels, and largest known air sacs may have reduced the weight of the animal by more than a ton in some instances, a useful evolutionary adaptation in animals that grow to more than 30 meters in length. In many hadrosaurs and theropod dinosaurs, the caudal vertebra is reinforced by a tortuous tendon. The presence of three or more sacral vertebrae, in relation to the hip bone, is one of the characteristics of dinosaurs. The occipital condyle is the structure of the posterior skull of the dinosaur that articulates with the first cervical vertebra.
See also
- Lower back pain
- Neuromechanical idiopathic scoliosis
- Neutral spine
References
External links
- Vertical column basics
- Term Spinal Terms
- VIRTUAL Spine - online learning resource
Source of the article : Wikipedia
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