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La columna vertebral, també anomenada espinada o espina (dorsal) (i popularment rosari de l'esquena)^[1] o raquis és el recobriment ossi de la medul·la espinal d'alguns animals, constituït per vèrtebres i que fa de suport de la resta dels ossos de l'esquelet. Els animals que la posseeixen es denominen vertebrats.

La columna vertebral està formada per 33 vèrtebres en total: set vèrtebres cervicals, dotze toràciques, cinc lumbars, cinc sacres (que habitualment estan soldades) i quatre coccigeals que formen el còccix. Aquestes vèrtebres s'articulen entre si a través de les caretes articulars i dels discos intervertebrals.

-> The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate, in which the notochord (a flexible rod of uniform composition) found in all chordates has been replaced by a segmented series of bones—vertebrae separated by intervertebral discs.^[2] The vertebral column houses the spinal canal, a cavity that encloses and protects the spinal cord.

There are about 50,000 species of animals that have a vertebral column.^[3] The human vertebral column is one of the most-studied examples.

Structure

In the human vertebral column there are normally thirty-three vertebrae;^[4] the upper twenty-four are articulating and separated from each other by intervertebral discs, and the lower nine are fused in adults, five in the sacrum and four in the coccyx or tailbone. The articulating vertebrae are named according to their region of the spine. There are seven cervical vertebrae, twelve thoracic vertebrae and five lumbar vertebrae. The number of vertebrae in a region can vary but overall the number remains the same. The number of those in the cervical region however is only rarely changed.^[5]

There are ligaments extending the length of the column at the front and the back, and in between the vertebrae joining the spinous processes, the transverse processes and the vertebral laminae.

Vertebrae

Plantilla:Main article

The vertebrae in the human vertebral column are divided into different regions, which correspond to the curves of the spinal column. The articulating vertebrae are named according to their region of the spine. Vertebrae in these regions are essentially alike, with minor variation. These regions are called the cervical spine, thoracic spine, lumbar spine, sacrum and coccyx. There are seven cervical vertebrae, twelve thoracic vertebrae and five lumbar vertebrae. The number of vertebrae in a region can vary but overall the number remains the same. The number of those in the cervical region however is only rarely changed.^[5] The vertebrae of the cervical, thoracic and lumbar spines are independent bones, and generally quite similar. The vertebrae of the sacrum and coccyx are usually fused and unable to move independently. Two special vertebrae are the atlas and axis, on which the head rests.

A typical vertebra consists of two parts: the vertebral body and the vertebral arch. The vertebral arch is posterior, meaning it faces the back of a person. Together, these enclose the vertebral foramen, which contains the spinal cord. Because the spinal cord ends in the lumbar spine, and the sacrum and coccyx are fused, they do not contain a central foramen. The vertebral arch is formed by a pair of pedicles and a pair of laminae, and supports seven processes, four articular, two transverse, and one spinous, the latter also being known as the neural spine. Two transverse processes and one spinous process are posterior to (behind) the vertebral body. The spinous process comes out the back, one transverse process comes out 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 are joints called facet joints. These restrict the range of movement possible, and are joined by a thin portion of the neural arch called the pars interarticularis. In between each pair of vertebrae are two small holes called intervertebral foramina. The spinal nerves leave the spinal cord through these holes.

Individual vertebrae are named according to their region and position. From top to bottom, the vertebrae are:

Cervical spine: 7 vertebrae (C1–C7)
Thoracic spine: 12 vertebrae (T1–T12)
Lumbar spine: 5 vertebrae (L1–L5)
Sacrum: 5 (fused) vertebrae (S1–S5)
Coccyx: 4 (3–5) (fused) vertebrae (Tailbone)

Shape

The upper cervical spine has a curve, convex forward, that begins at the axis (second cervical vertebra) at the apex of the odontoid process or dens, and ends at the middle of the second thoracic vertebra; it is the least marked of all the curves. This inward curve is known as a lordotic curve.

The thoracic curve, concave forward, begins at the middle of the second and ends at the middle of the twelfth thoracic vertebra. Its most prominent point behind corresponds to the spinous process of the seventh thoracic vertebra. This curve is known as a kyphotic curve.

The lumbar curve is more marked in the female than in the male; it begins at the middle of the last thoracic vertebra, and ends at the sacrovertebral angle. It is convex anteriorly, the convexity of the lower three vertebrae being much greater than that of the upper two. This curve is described as a lordotic curve.

The sacral curve begins at the sacrovertebral articulation, and ends at the point of the coccyx; its concavity is directed downward and forward as a kyphotic curve.

The thoracic and sacral kyphotic curves are termed primary curves, because they are present in the fetus. The cervical and lumbar curves are compensatory or secondary, and are developed after birth. The cervical curve forms when the infant is able to hold up its head (at three or four months) and to sit upright (at nine months). The lumbar curve forms later from twelve to eighteen months, when the child begins to walk.

Surfaces

Anterior surface

When viewed from in front, the width of the bodies of the vertebrae is seen to increase from the second cervical to the first thoracic; there is then a slight diminution in the next three vertebrae; below this there is again a gradual and progressive increase in width as low as the sacrovertebral angle. From this point there is a rapid diminution, to the apex of the coccyx.^[6]

Posterior surface

From behind, the vertebral column presents in the median line the spinous processes. In the cervical region (with the exception of the second and seventh vertebrae) these are short, horizontal and bifid. In the upper part of the thoracic region they are directed obliquely downward; in the middle they are almost vertical, and in the lower part they are nearly horizontal. In the lumbar region they are nearly horizontal. The spinous processes are separated by considerable intervals in the lumbar region, by narrower intervals in the neck, and are closely approximated in the middle of the thoracic region. Occasionally one of these processes deviates a little from the median line — which can sometimes be indicative of a fracture or a displacement of the spine. On either side of the spinous processes is the vertebral groove formed by the laminae in the cervical and lumbar regions, where it is shallow, and by the laminae and transverse processes in the thoracic region, where it is deep and broad; these grooves lodge the deep muscles of the back. Lateral to the spinous processes are the articular processes, and still more laterally the transverse processes. In the thoracic region, the transverse processes stand backward, on a plane considerably behind that of the same processes in the cervical and lumbar regions. In the cervical region, the transverse processes are placed in front of the articular processes, lateral to the pedicles and between the intervertebral foramina. In the thoracic region they are posterior to the pedicles, intervertebral foramina, and articular processes. In the lumbar region they are in front of the articular processes, but behind the intervertebral foramina.^[6]

Lateral surfaces

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 bodies of the vertebrae are marked in the back by the facets for articulation with the heads of the ribs. More posteriorly are the intervertebral foramina, formed by the juxtaposition of the vertebral notches, oval in shape, smallest in the cervical and upper part of the thoracic regions, and gradually increasing in size to the last lumbar. They transmit the special spinal nerves and are situated between the transverse processes in the cervical region, and in front of them in the thoracic and lumbar regions.^[6]

Ligaments

There are different ligaments involved in the holding together of the vertebrae in the column, and in the column's movement. The anterior and posterior longitudinal ligaments extend the length of the vertebral column along the front and back of the vertebral bodies.^[7] The interspinous ligaments connect the adjoining spinous processes of the vertebrae.^[8] The supraspinous ligament extends the length of the spine running along the back of the spinous processes, from the sacrum to the seventh cervical vertebra.^[9] From there it is continuous with the nuchal ligament.

Development

The striking segmented pattern of the spine is established during embryogenesis when somites are rhythmically added to the posterior of the embryo. Somite formation begins around the third week when the embryo begins gastrulation and continues until around 52 somites are formed. The somites are spheres, formed from the paraxial mesoderm that lies at the sides of the neural tube and they contain the precursors of spinal bone, the vertebrae ribs and some of the skull, as well as muscle, ligaments and skin. Somitogenesis and the subsequent distribution of somites is controlled by a clock and wavefront model acting in cells of the paraxial mesoderm. Soon after their formation, sclerotomes, which give rise to some of the bone of the skull, the vertebrae and ribs, migrate, leaving the remainder of the somite now termed a dermamyotome behind. This then splits to give the myotomes which will form the muscles and dermatomes which will form the skin of the back. Sclerotomes become subdivided into an anterior and a posterior compartment. This subdivision plays a key role in the definitive patterning of vertebrae that form when the posterior part of one somite fuses to the anterior part of the consecutive somite during a process termed resegmentation. Disruption of the somitogenesis process in humans results in diseases such as congenital scoliosis. So far, the human homologues of three genes associated to the mouse segmentation clock, (MESP2, DLL3 and LFNG), have been shown to be mutated in cases of congenital scoliosis, suggesting that the mechanisms involved in vertebral segmentation are conserved across vertebrates. In humans the first four somites are incorporated in the base of the occipital bone of the skull and the next 33 somites will form the vertebrae, ribs, muscles, ligaments and skin.^[10] The remaining posterior somites degenerate. During the fourth week of embryogenesis, the sclerotomes shift their position to surround the spinal cord and the notochord. This column of tissue has a segmented appearance, with alternating areas of dense and less dense areas.

As the sclerotome develops, it condenses further eventually developing into the vertebral body. Development of the appropriate shapes of the vertebral bodies is regulated by HOX genes.

The less dense tissue that separates the sclerotome segments develop into the intervertebral discs.

The notochord disappears in the sclerotome (vertebral body) segments, but persists in the region of the intervertebral discs as the nucleus pulposus. The nucleus pulposus and the fibers of the anulus fibrosus make up the intervertebral disc.

The primary curves (thoracic and sacral curvatures) form during fetal development. The secondary curves develop after birth. The cervical curvature forms as a result of lifting the head and the lumbar curvature forms as a result of walking.

Function

Spinal cord

Plantilla:Main article The vertebral column surrounds the spinal cord which travels within the spinal canal, formed from a central hole within each vertebra. The spinal cord is part of the central nervous system that supplies nerves and receives information from the peripheral nervous system within the body. The spinal cord consists of grey and white matter and a central cavity, the central canal. Adjacent to each vertebra emerge spinal nerves. The spinal nerves provide sympathetic nervous supply to the body, with nerves emerging forming the sympathetic trunk and the splanchnic nerves.

The spinal canal follows the different curves of the column; it is large and triangular in those parts of the column which enjoy the greatest freedom of movement, such as the cervical and lumbar regions; and is small and rounded in the thoracic region, where motion is more limited.^{[cal citació]}

The spinal cord terminates in the conus medullaris and cauda equina.

Clinical significance

Disease

Spina bifida is a congenital disorder in which there is a defective closure of the vertebral arch. Sometimes the spinal meninges and also the spinal cord can protrude through this, and this is called Spina bifida cystica. Where the condition does not involve this protrusion it is known as Spina bifida occulta. Sometimes all of the vertebral arches may remain incomplete.^[11] Another, though rare, congenital disease is Klippel-Feil syndrome which is the fusion of any two of the cervical vertebrae.

Spondylolisthesis is the forward displacement of a vertebra and retrolisthesis is a posterior displacement of one vertebral body with respect to the adjacent vertebra to a degree less than a dislocation.

Spinal disc herniation, more commonly called a "slipped disc", is the result of a tear in the outer ring (anulus fibrosus) of the intervertebral disc, which lets some of the soft gel-like material, the nucleus pulposus, bulge out in a hernia.

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 stenosis can constrict the spinal canal giving rise to a neurological deficit.

Pain at the coccyx (tailbone) is known as coccydynia.^[12]

Spinal cord injury is damage to the spinal cord that causes changes in its function, either temporary or permanent.

Curvature

Excessive or abnormal spinal curvature is classed as a spinal disease or dorsopathy and includes the following abnormal curvatures:

Kyphosis is an exaggerated kyphotic (concave) curvature in the thoracic region, also called hyperkyphosis. This produces the so-called "humpback" or "dowager's hump", a condition commonly resulting from osteoporosis.
Lordosis as an exaggerated lordotic (convex) curvature of the lumbar region, is known as lumbar hyperlordosis and also as "swayback". Temporary lordosis is common during pregnancy.
Scoliosis, lateral curvature, is the most common abnormal curvature, occurring in 0.5% of the population. 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. It can also be caused by pulmonary atelectasis (partial or complete deflation of one or more lobes of the lungs) as observed in asthma or pneumothorax.
Kyphoscoliosis, a combination of kyphosis and scoliosis.

Anatomical landmarks

Orientation of vertebral column on surface. T3 is at level of medial part of spine of scapula T7 is at inferior angle of the scapula. L4 is at highest point of iliac crest. S2 is at the level of posterior superior iliac spine. Also C7 is easily localized as a prominence at the lower part of the neck.^[13]

Individual vertebrae of the human vertebral column can be felt and used as surface anatomy, with reference points are taken from the middle of the vertebral body. This provides anatomical landmarks that can be used to guide procedures such as a lumbar puncture and also as vertical reference points to describe the locations of other parts of human anatomy, such as the positions of organs.

Other animals

Variations in vertebrae

The general structure of vertebrae in other animals is largely the same as in humans. Individual vertebrae are composed of a centrum (body), arches protruding from the top and bottom of the centrum, and various processes projecting from the centrum and/or arches. An arch extending from the top of the centrum is called a neural arch, while the haemal arch or chevron is found underneath the centrum in the caudal (tail) vertebrae of fish, most reptiles, some birds, some dinosaurs and some mammals with long tails. The vertebral processes can either give the structure rigidity, help them articulate with ribs, or serve as muscle attachment points. Common types are transverse process, diapophyses, parapophyses, and zygapophyses (both the cranial zygapophyses and the caudal zygapophyses). The centrum of the vertebra can be classified based on the fusion of its elements. In temnospondyls, bones such as the spinous process, the pleurocentrum and the intercentrum are separate ossifications. Fused elements, however, classify a vertebra as having holospondyly.

A vertebra can also be described in terms of the shape of the ends of the centrum. Centra with flat ends are acoelous, like those in mammals. These flat ends of the centra are especially good at supporting and distributing compressive forces. Amphicoelous vertebra have centra with both ends concave. This shape is common in fish, where most motion is limited. Amphicoelous centra often are integrated with a full notochord. Procoelous vertebrae are anteriorly concave and posteriorly convex. They are found in frogs and modern reptiles. Opisthocoelous vertebrae are the opposite, possessing anterior convexity and posterior concavity. They are found in salamanders, and in some non-avian dinosaurs. Heterocoelous vertebrae have saddle-shaped articular surfaces. This type of configuration is seen in turtles that retract their necks, and birds, because it permits extensive lateral and vertical flexion motion without stretching the nerve cord too extensively or wringing it about its long axis.

In horses, the Arabian (breed) can have one less vertebrae and pair of ribs. This anomaly disappears in foals that are the product of an Arabian and another breed of horse.^[14]

Regional vertebrae

Vertebrae are defined by the regions of the vertebral column that they occur in, as in humans. Cervical vertebrae are those in the neck area. With the exception of the two sloth genera (Choloepus and Bradypus) and the manatee genus, (Trichechus),^[15] all mammals have seven cervical vertebrae.^[16] In other vertebrates, the number of cervical vertebrae can range from a single vertebra in amphibians, to as many as 25 in swans or 76 in the extinct plesiosaur Elasmosaurus. The dorsal vertebrae range from the bottom of the neck to the top of the pelvis. Dorsal vertebrae attached to the ribs are called thoracic vertebrae, while those without ribs are called lumbar vertebrae. 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. When multiple sacral vertebrae are fused into a single structure, it is called the sacrum. 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. 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).

Fish and amphibians

The vertebrae of lobe-finned fishes consist of three discrete bony elements. The vertebral arch surrounds the spinal cord, and is of broadly similar form to that found in most other vertebrates. Just beneath the arch lies a small plate-like pleurocentrum, which protects the upper surface of the notochord, and below that, a larger arch-shaped intercentrum to protect the lower border. Both of these structures are embedded within a single cylindrical mass of cartilage. A similar arrangement was found in the primitive Labyrinthodonts, but in the evolutionary line that led to reptiles (and hence, also to mammals and birds), the intercentrum became partially or wholly replaced by an enlarged pleurocentrum, which in turn became the bony vertebral body.^[17] In most ray-finned fishes, including all teleosts, these two structures are fused with, and embedded within, a solid piece of bone superficially resembling the vertebral body of mammals. In living amphibians, there is simply a cylindrical piece of bone below the vertebral arch, with no trace of the separate elements present in the early tetrapods.^[17]

In cartilaginous fish, such as sharks, the vertebrae consist of two cartilaginous tubes. The upper tube is formed from the vertebral arches, but also includes additional cartilaginous structures filling in the gaps between the vertebrae, and so enclosing the spinal cord in an essentially continuous sheath. The lower tube surrounds the notochord, and has a complex structure, often including multiple layers of calcification.^[17]

Lampreys have vertebral arches, but nothing resembling the vertebral bodies found in all higher vertebrates. Even the arches are discontinuous, consisting of separate pieces of arch-shaped cartilage around the spinal cord in most parts of the body, changing to long strips of cartilage above and below in the tail region. Hagfishes lack a true vertebral column, and are therefore not properly considered vertebrates, but a few tiny neural arches are present in the tail.^[17]

Other vertebrates

The general structure of human vertebrae is fairly typical of that found in mammals, reptiles, and birds. The shape of the vertebral body does, however, vary somewhat between different groups. In mammals, such as humans, it typically has flat upper and lower surfaces, while in reptiles the anterior surface commonly has a concave socket into which the expanded convex face of the next vertebral body fits. 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. Some unusual variations include the saddle-shaped sockets between the cervical vertebrae of birds and the presence of a narrow hollow canal running down the centre of the vertebral bodies of geckos and tuataras, containing a remnant of the notochord.^[17]

Reptiles often retain the primitive intercentra, which are present as small crescent-shaped bony elements lying between the bodies of adjacent vertebrae; similar structures are often found in the caudal vertebrae of mammals. 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. These latter bones are probably homologous with the ventral ribs of fish. The number of vertebrae in the spines of reptiles is highly variable, and may be several hundred in some species of snake.^[17]

In birds, there is a variable number of cervical vertebrae, which often form the only truly flexible part of the spine. The thoracic vertebrae are partially fused, providing a solid brace for the wings during flight. The sacral vertebrae are fused with the lumbar vertebrae, and some thoracic and caudal vertebrae, to form a single structure, the synsacrum, which is thus of greater relative length than the sacrum of mammals. In living birds, the remaining caudal vertebrae are fused into a further bone, the pygostyle, for attachment of the tail feathers.^[17]

Aside from the tail, the number of vertebrae in mammals is generally fairly constant. There are almost always seven cervical vertebrae (sloths and manatees are among the few exceptions), followed by around twenty or so further vertebrae, divided between the thoracic and lumbar forms, depending on the number of ribs. There are generally three to five vertebrae with the sacrum, and anything up to fifty caudal vertebrae.^[17]

Dinosaurs

The vertebral column in dinosaurs consists of the cervical (neck), dorsal (back), sacral (hips), and caudal (tail) vertebrae. Dinosaur vertebrae possess features known as pleurocoels, which are hollow depressions on the lateral portions of the vertebrae, which served to decrease the weight of these bones without sacrificing strength. Many researchers think that these pleurocoels were filled with air sacs, which would have further decreased weight. In sauropod dinosaurs, the largest known land vertebrates, pleurocoels may have reduced the animal's weight by over a ton in some instances, a handy evolutionary adaption in animals that grew to over 30 metres in length. In many hadrosaur and theropod dinosaurs, the caudal vertebrae were reinforced by ossified tendons. The presence of three or more sacral vertebrae, in association with the hip bones, is one of the defining characteristics of dinosaurs. The occipital condyle is a structure on the posterior part of a dinosaur's skull which articulates with the first cervical vertebra.^[18]

References

A Wikimedia Commons hi ha contingut multimèdia relatiu a: Columna vertebral

↑ Rosari, en diccionari.cat
↑ Liem, Karel F.. Functional anatomy of the vertebrates: an evolutionary perspective. Harcourt College Publishers, 2001, p. 277. ISBN 978-0-03-022369-3.
↑ David Krogh (2010), Biology: A Guide to the Natural World, Benjamin-Cummings Publishing Company, p. 333, ISBN 978-0-321-61655-5, <https://books.google.com/books?id=Ph7NSAAACAAJ>
↑ Drake, Richard L. Gray's anatomy for students. Philadelphia: Elsevier/Churchill Livingstone, 2005, p. 17. ISBN 978-0-8089-2306-0.
↑ ^5,0 ^5,1 Gray, Henry. Gray's Anatomy. New York: Crown Publishers, Inc., 1977, p. 34.
↑ ^6,0 ^6,1 ^6,2 Gray's Anatomy (1918)
↑ Nigel Palastanga. Churchill Livingstone. Anatomy and Human Movement: Structure and Function., 2012.
↑ «interspinal ligament». Merriam-Webster. [Consulta: 29 gener 2016].
↑ Drake, Richard L.; Vogl, Wayne; Tibbitts, Adam W.M. Mitchell ; illustrations by Richard [et al.].. Gray's anatomy for students. Pbk.. Philadelphia: Elsevier/Churchill Livingstone, 2005, p. 45. ISBN 978-0-443-06612-2.
↑ Somites, Spinal Ganglia, and Centra Arxivat July 15, 2016, a Wayback Machine.
↑ Dorland's. Dorland's Illustrated Medical Dictionary. 32nd. Elsevier Saunders, 2012, p. 1748. ISBN 978-1-4160-6257-8.
↑ Patel, R; Appannagari, A; Whang, P.G. «Coccydynia». Current Reviews in Musculoskeletal Medicine, vol. 1, 3-4, May 2008, pàg. 223–226. DOI: 10.1007/s12178-008-9028-1. PMID: 19468909.
↑ Anatomy Compendium (Godfried Roomans and Anca Dragomir)
↑ Edwards, The Arabian, pp. 27–28
↑ «Sticking Their Necks out for Evolution: Why Sloths and Manatees Have Unusually Long (or Short) Necks». May 6th 2011. Science Daily. [Consulta: 25 juliol 2013].
↑ Frietson Galis «Why do almost all mammals have seven cervical vertebrae? Developmental constraints, Hox genes and Cancer». Journal of experimental zoology, vol. 285, 1, 1999, pàg. 19–26. DOI: 10.1002/(SICI)1097-010X(19990415)285:1<19::AID-JEZ3>3.0.CO;2-Z. PMID: 10327647.
↑ ^17,0 ^17,1 ^17,2 ^17,3 ^17,4 ^17,5 ^17,6 ^17,7 Romer, Alfred Sherwood. The Vertebrate Body. Philadelphia, PA: Holt-Saunders International, 1977, p. 161–170. ISBN 0-03-910284-X.
↑ Martin, A.J. (2006). Introduction to the Study of Dinosaurs. Second Edition. Oxford, Blackwell Publishing. pg. 299-300. ISBN 1-4051-3413-5.

External links

Vegeu spine en el Viccionari, el diccionari lliure.

->

Referències

A Wikimedia Commons hi ha contingut multimèdia relatiu a: Columna vertebral

Autòpsia del Raquis. Article d'accés en línia gratuït de la Revista Española de Medicina Legal

[1] Rosari, en diccionari.cat

[2] Liem, Karel F.. Functional anatomy of the vertebrates: an evolutionary perspective. Harcourt College Publishers, 2001, p. 277. ISBN 978-0-03-022369-3.

[Krogh2010-3] David Krogh (2010), Biology: A Guide to the Natural World, Benjamin-Cummings Publishing Company, p. 333, ISBN 978-0-321-61655-5, <https://books.google.com/books?id=Ph7NSAAACAAJ>

[GRAYS2005-4] Drake, Richard L. Gray's anatomy for students. Philadelphia: Elsevier/Churchill Livingstone, 2005, p. 17. ISBN 978-0-8089-2306-0.

[Gray_1977_34-5] 5,0 ^5,1 Gray, Henry. Gray's Anatomy. New York: Crown Publishers, Inc., 1977, p. 34.

[GRAY1918-6] 6,0 ^6,1 ^6,2 Gray's Anatomy (1918)

[7] Nigel Palastanga. Churchill Livingstone. Anatomy and Human Movement: Structure and Function., 2012.

[8] «interspinal ligament». Merriam-Webster. [Consulta: 29 gener 2016].

[9] Drake, Richard L.; Vogl, Wayne; Tibbitts, Adam W.M. Mitchell ; illustrations by Richard [et al.].. Gray's anatomy for students. Pbk.. Philadelphia: Elsevier/Churchill Livingstone, 2005, p. 45. ISBN 978-0-443-06612-2.

[10] Somites, Spinal Ganglia, and Centra Arxivat July 15, 2016, a Wayback Machine.

[11] Dorland's. Dorland's Illustrated Medical Dictionary. 32nd. Elsevier Saunders, 2012, p. 1748. ISBN 978-1-4160-6257-8.

[review-12] Patel, R; Appannagari, A; Whang, P.G. «Coccydynia». Current Reviews in Musculoskeletal Medicine, vol. 1, 3-4, May 2008, pàg. 223–226. DOI: 10.1007/s12178-008-9028-1. PMID: 19468909.

[13] Anatomy Compendium (Godfried Roomans and Anca Dragomir)

[GBE73p27-14] Edwards, The Arabian, pp. 27–28

[15] «Sticking Their Necks out for Evolution: Why Sloths and Manatees Have Unusually Long (or Short) Necks». May 6th 2011. Science Daily. [Consulta: 25 juliol 2013].

[16] Frietson Galis «Why do almost all mammals have seven cervical vertebrae? Developmental constraints, Hox genes and Cancer». Journal of experimental zoology, vol. 285, 1, 1999, pàg. 19–26. DOI: 10.1002/(SICI)1097-010X(19990415)285:1<19::AID-JEZ3>3.0.CO;2-Z. PMID: 10327647.

[VB-17] 17,0 ^17,1 ^17,2 ^17,3 ^17,4 ^17,5 ^17,6 ^17,7 Romer, Alfred Sherwood. The Vertebrate Body. Philadelphia, PA: Holt-Saunders International, 1977, p. 161–170. ISBN 0-03-910284-X.

[18] Martin, A.J. (2006). Introduction to the Study of Dinosaurs. Second Edition. Oxford, Blackwell Publishing. pg. 299-300. ISBN 1-4051-3413-5.

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@@ Línia 1: / Línia 1: @@
+{{inacabat|jaumellecha}}
 [[File:Spinal column curvature ca.svg|thumb|Diferents parts de la columna vertebral]]
 La '''columna vertebral''', també anomenada '''espinada''' o '''espina''' (dorsal) (i popularment '''rosari de l'esquena''')<ref>[http://www.diccionari.cat/lexicx.jsp?GECART=0119962 Rosari], en diccionari.cat</ref> o '''raquis''' és el recobriment [[os]]si de la [[medul·la espinal]] d'alguns animals, constituït per [[vèrtebres]] i que fa de suport de la resta dels ossos de l'esquelet. Els animals que la posseeixen es denominen [[vertebrats]].
@@ Línia 5: / Línia 7: @@
 Aquestes vèrtebres s'articulen entre si a través de les caretes articulars i dels [[Disc intervertebral|discos intervertebrals]].
+->
+The '''vertebral column''', also known as the '''backbone''' or '''spine''', is part of the [[axial skeleton]]. The vertebral column is the defining characteristic of a [[vertebrate]], in which the [[notochord]] (a flexible rod of uniform composition) found in all [[Chordata|chordates]] has been replaced by a segmented series of [[bone]]s—[[vertebra]]e separated by [[intervertebral disc]]s.<ref>{{cite book|title=Functional anatomy of the vertebrates: an evolutionary perspective|year=2001|publisher=Harcourt College Publishers|isbn=978-0-03-022369-3|author=Liem, Karel F.|author2=Warren Franklin Walker|page=277}}</ref> The vertebral column houses the [[spinal canal]], a cavity that encloses and protects the [[spinal cord]].
+There are about 50,000 species of animals that have a vertebral column.<ref name="Krogh2010">{{citation|author=David Krogh|title=Biology: A Guide to the Natural World|url=https://books.google.com/books?id=Ph7NSAAACAAJ|date=2010|publisher=Benjamin-Cummings Publishing Company|isbn=978-0-321-61655-5|page=333}}</ref> The human vertebral column is one of the most-studied examples.
+==Structure==
+In the human vertebral column there are normally thirty-three vertebrae;<ref name=GRAYS2005>{{cite book|last=Drake|first=Richard L.|title=Gray's anatomy for students|year=2005|publisher=Elsevier/Churchill Livingstone|location=Philadelphia|isbn=978-0-8089-2306-0|author2=Vogl, Wayne |author3=Tibbitts, Adam W.M. Mitchell  |author4=illustrations by Richard |author5= Richardson, Paul |page=17}}</ref> the upper twenty-four are articulating and separated from each other by [[intervertebral disc]]s, and the lower nine are fused in adults, five in the [[sacrum]] and four in the [[coccyx]] or ''tailbone''.
+The articulating vertebrae are named according to their region of the spine. There are seven [[cervical vertebrae]], twelve [[thoracic vertebrae]] and five [[lumbar vertebrae]].
+The number of vertebrae in a region can vary but overall the number remains the same. The number of those in the cervical region however is only rarely changed.<ref name="Gray 1977 34">{{cite book|last=Gray|first=Henry|title=Gray's Anatomy|year=1977|publisher=Crown Publishers, Inc.|location=New York|pages=34}}</ref>
+There are [[ligament]]s extending the length of the column at the front and the back, and in between the vertebrae joining the [[spinous process]]es, the [[transverse process]]es and the vertebral laminae.
+===Vertebrae===
+{{Main article|Vertebra}}
+[[File:Gray 111 - Vertebral column-coloured.png|thumb|left|150px|Numbering order of the vertebrae of the human spinal column]]
+The vertebrae in the human vertebral column are divided into different regions, which correspond to the curves of the spinal column. The articulating vertebrae are named according to their region of the spine.  Vertebrae in these regions are essentially alike, with minor variation. These regions are called the [[Cervical vertebrae|cervical spine]], [[Thoracic vertebrae|thoracic spine]], [[Lumbar vertebrae|lumbar spine]], [[sacrum]] and [[coccyx]].
+There are seven cervical vertebrae, twelve thoracic vertebrae and five lumbar vertebrae. The number of vertebrae in a region can vary but overall the number remains the same. The number of those in the cervical region however is only rarely changed.<ref name="Gray 1977 34"/> The vertebrae of the cervical, thoracic and lumbar spines are independent bones, and generally quite similar. The vertebrae of the sacrum and coccyx are usually fused and unable to move independently. Two special vertebrae are the [[atlas (anatomy)|atlas]] and [[axis (anatomy)|axis]], on which the head rests.
+[[File:718 Vertebra-en.svg|500px|thumb|Anatomy of a vertebra]]
+A typical vertebra consists of two parts: the [[vertebral body]] and the [[vertebral arch]]. The vertebral arch is [[posterior (anatomy)|posterior]], meaning it faces the back of a person. Together, these enclose the [[vertebral foramen]], which contains the [[spinal cord]]. Because the spinal cord ends in the lumbar spine, and the sacrum and coccyx are fused, they do not contain a central foramen. The vertebral arch is formed by a pair of [[Pedicle of vertebral arch|pedicles]] and a pair of [[lamina of the vertebral arch|laminae]], and supports seven [[Process (anatomy)|processes]], four articular, two transverse, and one spinous, the latter also being known as the neural spine. Two [[transverse process]]es and one [[spinous process]] are posterior to (behind) the vertebral body. The spinous process comes out the back, one transverse process comes out 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 are joints called [[facet joint]]s. These restrict the range of movement possible, and are joined by a thin portion of the neural arch called the ''[[pars interarticularis]]''. In between each pair of vertebrae are two small holes called [[intervertebral foramina]]. The [[spinal nerve]]s leave the [[spinal cord]] through these holes.
+Individual vertebrae are named according to their region and position. From top to bottom, the vertebrae are:
+*[[Cervical vertebrae|Cervical spine]]: 7 vertebrae (C1–C7)
+*[[Thoracic vertebrae|Thoracic spine]]: 12 vertebrae (T1–T12)
+*[[Lumbar vertebrae|Lumbar spine]]: 5 vertebrae (L1–L5)
+*[[Sacral vertebrae|Sacrum]]: 5 (fused) vertebrae (S1–S5)
+*[[Coccygeal vertebrae|Coccyx]]: 4 (3–5) (fused) vertebrae (Tailbone)
+{{Clear}}
+===Shape===
+The upper cervical spine has a curve, convex forward, that begins at the [[axis (anatomy)|axis]] (second cervical vertebra) at the apex of the odontoid process or [[axis (anatomy)#Dens|dens]], and ends at the middle of the second thoracic vertebra; it is the least marked of all the curves. This inward curve is known as a [[lordosis|lordotic]] curve.
+The thoracic curve, concave forward, begins at the middle of the second and ends at the middle of the twelfth thoracic vertebra. Its most prominent point behind corresponds to the spinous process of the seventh thoracic vertebra. This curve is known as a [[kyphosis|kyphotic]] curve.
+The lumbar curve is more marked in the [[female]] than in the [[male]]; it begins at the middle of the last thoracic vertebra, and ends at the sacrovertebral angle. It is convex anteriorly, the convexity of the lower three vertebrae being much greater than that of the upper two. This curve is described as a [[lordosis|lordotic]] curve.
+The sacral curve begins at the sacrovertebral articulation, and ends at the point of the [[coccyx]]; its concavity is directed downward and forward as a kyphotic curve.
+The thoracic and sacral kyphotic curves are termed primary curves, because they are present in the [[fetus]]. The cervical and lumbar curves are ''compensatory'' or ''secondary'', and are developed after [[childbirth|birth]]. The cervical curve forms when the infant is able to hold up its head (at three or four months) and to sit upright (at nine months). The lumbar curve forms later from twelve to eighteen months, when the child begins to walk.
+===Surfaces===
+;Anterior surface
+When viewed from in front, the width of the bodies of the vertebrae is seen to increase from the second cervical to the first thoracic; there is then a slight diminution in the next three vertebrae; below this there is again a gradual and progressive increase in width as low as the sacrovertebral angle. From this point there is a rapid diminution, to the apex of the coccyx.<ref name=GRAY1918>Gray's Anatomy (1918)</ref>
+;Posterior surface
+From behind, the vertebral column presents in the median line the spinous processes. In the cervical region (with the exception of the second and seventh vertebrae) these are short, horizontal and bifid. In the upper part of the thoracic region they are directed obliquely downward; in the middle they are almost vertical, and in the lower part they are nearly horizontal. In the lumbar region they are nearly horizontal. The spinous processes are separated by considerable intervals in the lumbar region, by narrower intervals in the neck, and are closely approximated in the middle of the thoracic region. Occasionally one of these processes deviates a little from the median line &mdash; which can sometimes be indicative of a fracture or a displacement of the spine. On either side of the spinous processes is the vertebral groove formed by the laminae in the cervical and lumbar regions, where it is shallow, and by the laminae and transverse processes in the thoracic region, where it is deep and broad; these grooves lodge the deep muscles of the back. Lateral to the spinous processes are the articular processes, and still more laterally the transverse processes. In the thoracic region, the transverse processes stand backward, on a plane considerably behind that of the same processes in the cervical and lumbar regions. In the cervical region, the transverse processes are placed in front of the articular processes, lateral to the pedicles and between the intervertebral foramina. In the thoracic region they are posterior to the pedicles, intervertebral foramina, and articular processes. In the lumbar region they are in front of the articular processes, but behind the intervertebral foramina.<ref name=GRAY1918/>
+;Lateral surfaces
+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 bodies of the vertebrae are marked in the back by the facets for articulation with the heads of the ribs. More posteriorly are the intervertebral foramina, formed by the juxtaposition of the vertebral notches, oval in shape, smallest in the cervical and upper part of the thoracic regions, and gradually increasing in size to the last lumbar. They transmit the special spinal nerves and are situated between the transverse processes in the cervical region, and in front of them in the thoracic and lumbar regions.<ref name=GRAY1918/>
+===Ligaments===
+There are different ligaments involved in the holding together of the vertebrae in the column, and in the column's movement. The [[anterior longitudinal ligament|anterior]] and [[posterior longitudinal ligament]]s extend the length of the vertebral column along the front and back of the vertebral bodies.<ref>{{cite book | author= Nigel Palastanga|author2=Roger W. Soames  | title= Anatomy and Human Movement: Structure and Function. | editor= Churchill Livingstone| edition=  | year= 2012| isbn= }}</ref> The [[interspinous ligament]]s connect the adjoining spinous processes of the vertebrae.<ref>{{Cite web|url=http://www.merriam-webster.com/medical/interspinal%20ligament|publisher=Merriam-Webster|title=interspinal ligament|accessdate=29 January 2016}}</ref> The [[supraspinous ligament]] extends the length of the spine running along the back of the spinous processes, from the sacrum to the [[vertebra prominens|seventh]] [[cervical vertebra]].<ref>{{cite book|last1=Drake|first1=Richard L.|last2=Vogl|first2=Wayne|last3=Tibbitts|first3=Adam W.M. Mitchell ; illustrations by Richard|last4=Richardson|first4=Paul|title=Gray's anatomy for students|date=2005|publisher=Elsevier/Churchill Livingstone|location=Philadelphia|isbn=978-0-443-06612-2|page=45|edition=Pbk.}}</ref> From there it is continuous with the [[nuchal ligament]].
+===Development===
+The striking [[segmentation (biology)|segmented]] pattern of the spine is established during [[human embryogenesis|embryogenesis]] when [[somites]] are rhythmically added to the posterior of the embryo. Somite formation begins around the third week when the embryo begins [[gastrulation]] and continues until around 52 somites are formed. The somites are spheres, formed from the [[paraxial mesoderm]] that lies at the sides of the neural tube and they contain the precursors of spinal bone, the vertebrae ribs and some of the skull, as well as muscle, ligaments and skin. [[Somitogenesis]] and the subsequent distribution of somites is controlled by a [[clock and wavefront model]] acting in cells of the paraxial mesoderm. Soon after their formation, [[sclerotome]]s, which give rise to some of the bone of the skull, the vertebrae and ribs, migrate, leaving the remainder of the somite now termed a dermamyotome behind. This then splits to give the [[myotome (embryology)|myotomes]] which will form the muscles and [[dermatome (embryology)|dermatome]]s which will form the skin of the back.  Sclerotomes become subdivided into an anterior and a posterior compartment. This subdivision plays a key role in the definitive patterning of vertebrae that form when the posterior part of one somite fuses to the anterior part of the consecutive somite during a process termed resegmentation. Disruption of the somitogenesis process in humans results in diseases such as congenital scoliosis. So  far, the human homologues of three genes associated to the mouse segmentation clock, (MESP2, DLL3 and LFNG), have been shown to be mutated in cases of congenital scoliosis, suggesting that the mechanisms involved in vertebral segmentation are conserved across vertebrates. In humans the first four somites are incorporated in the base of the [[occipital bone]] of the skull and the next 33 somites will form the vertebrae, ribs, muscles, ligaments and skin.<ref>[http://content.karger.com/ProdukteDB/produkte.asp?Aktion=ShowFulltext&ArtikelNr=68948&Ausgabe=228995&ProduktNr=224197 Somites, Spinal Ganglia, and Centra<!-- Bot generated title -->] {{webarchive |url=https://web.archive.org/web/20160715114832/http://content.karger.com/ProdukteDB/produkte.asp?Aktion=ShowFulltext&ArtikelNr=68948&Ausgabe=228995&ProduktNr=224197 |date=July 15, 2016 }}</ref> The remaining posterior somites degenerate. During the fourth week of [[human embryogenesis|embryogenesis]], the [[sclerotome]]s shift their position to surround the [[spinal cord]] and the [[notochord]]. This column of tissue has a segmented appearance, with alternating areas of dense and less dense areas.
+As the sclerotome develops, it condenses further eventually developing into the [[vertebral body]]. Development of the appropriate shapes of the vertebral bodies is regulated by ''[[HOX gene]]s''.
+The less dense tissue that separates the sclerotome segments develop into the [[intervertebral disc]]s.
+The notochord disappears in the sclerotome (vertebral body) segments, but persists in the region of the intervertebral discs as the [[nucleus pulposus]]. The nucleus pulposus and the fibers of the [[anulus fibrosus disci intervertebralis|anulus fibrosus]] make up the intervertebral disc.
+The primary curves (thoracic and sacral curvatures) form during fetal development. The secondary curves develop after birth. The cervical curvature forms as a result of lifting the head and the lumbar curvature forms as a result of walking.
+==Function==
+===Spinal cord===
+[[File:Spinal cord direv.svg|thumbnail|The [[spinal cord]] nested in the vertebral column.]]
+{{Main article|Spinal cord}}
+The vertebral column surrounds the spinal cord which travels within the [[spinal canal]], formed from a central hole within each [[spinal vertebrae|vertebra]]. The spinal cord is part of the [[central nervous system]] that supplies nerves and receives information from the [[peripheral nervous system]] within the body. The spinal cord consists of [[grey matter|grey]] and [[white matter]] and a central cavity, the [[central canal of spinal cord|central canal]]. Adjacent to each vertebra emerge [[spinal nerve]]s. The spinal nerves provide [[Sympathetic nervous system|sympathetic nervous supply]] to the body, with nerves emerging forming the [[sympathetic trunk]] and the [[splanchnic nerve]]s.
+The [[spinal canal]] follows the different curves of the column; it is large and triangular in those parts of the column which enjoy the greatest freedom of movement, such as the cervical and lumbar regions; and is small and rounded in the thoracic region, where motion is more limited.{{citation needed|date=January 2011}}
+The spinal cord terminates in the [[conus medullaris]] and [[cauda equina]].
+==Clinical significance==
+===Disease===
+[[Spina bifida]] is a [[congenital vertebral anomaly|congenital disorder]] in which there is a defective closure of the vertebral arch. Sometimes the spinal [[meninges]] and also the spinal cord can protrude through this, and this is called ''Spina bifida cystica''. Where the condition does not involve this protrusion it is known as ''Spina bifida occulta''. Sometimes all of the vertebral arches may remain incomplete.<ref>{{cite book|last1=Dorland's|title=Dorland's Illustrated Medical Dictionary|date=2012|publisher=Elsevier Saunders|isbn=978-1-4160-6257-8|page=1748|edition=32nd}}</ref>
+Another, though rare, congenital disease is [[Klippel-Feil syndrome]] which is the fusion of any two of the cervical vertebrae.
+[[Spondylolisthesis]] is the forward displacement of a vertebra and [[retrolisthesis]] is a posterior displacement of one [[vertebral body]] with respect to the adjacent vertebra to a degree less than a dislocation.
+[[Spinal disc herniation]], more commonly called a "slipped disc", is the result of a tear in the outer ring ([[Anulus fibrosus disci intervertebralis|anulus  fibrosus]]) of the [[intervertebral disc]], which lets some of the soft gel-like material, the [[nucleus pulposus]], bulge out in a [[hernia]].
+[[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 stenosis can constrict the spinal canal giving rise to a [[functional neurological deficit|neurological deficit]].
+Pain at the [[coccyx]] (tailbone) is known as [[coccydynia]].<ref name="review">{{cite journal|last1=Patel|first1=R|last2=Appannagari|first2=A|last3=Whang|first3=P.G.|title=Coccydynia|journal=Current Reviews in Musculoskeletal Medicine|date=May 2008|volume=1|issue=3-4|pages=223–226|doi= 10.1007/s12178-008-9028-1|pmid=19468909}}</ref>
+[[Spinal cord injury]] is damage to the [[spinal cord]] that causes changes in its function, either temporary or permanent.
+===Curvature===
+Excessive or abnormal spinal curvature is classed as a [[spinal disease]] or dorsopathy and includes the following abnormal curvatures:
+* [[Kyphosis]] is an exaggerated kyphotic (concave) curvature in the thoracic region, also called hyperkyphosis. This produces the so-called "humpback" or "dowager's hump", a condition commonly resulting from [[osteoporosis]].
+* [[Lordosis]] as an exaggerated lordotic (convex) curvature of the lumbar region, is known as [[lumbar hyperlordosis]] and also as "swayback". Temporary lordosis is common during [[Maternal physiological changes in pregnancy#Musculoskeletal|pregnancy]].
+* [[Scoliosis]], lateral curvature, is the most common abnormal curvature, occurring in 0.5% of the population. It is more common among [[female]]s and may result from unequal growth of the two sides of one or more vertebrae, so that they do not fuse properly.  It can also be caused by pulmonary [[atelectasis]] (partial or complete deflation of one or more lobes of the lungs) as observed in [[asthma]] or [[pneumothorax]].
+* [[Kyphoscoliosis]], a combination of kyphosis and scoliosis.
+===Anatomical landmarks===
+[[Image:Orientation.PNG|thumb|Orientation of vertebral column on surface. T3 is at level of medial part of [[spine of scapula]] T7 is at [[inferior angle of the scapula]]. L4 is at highest point of [[iliac crest]]. S2 is at the level of [[posterior superior iliac spine]]. Also C7 is easily localized as a prominence at the lower part of the neck.<ref>Anatomy Compendium (Godfried Roomans and Anca Dragomir)</ref>]]
+[[File:Surface projections of the organs of the trunk.png|thumb|240px|Surface projections of organs of the [[torso]]. The [[transpyloric line]] is seen at [[lumbar vertebra 1|L1]]]]
+Individual vertebrae of the human vertebral column can be felt and used as [[surface anatomy]], with reference points are taken from the middle of the vertebral body. This provides [[anatomical landmark]]s that can be used to guide procedures such as a [[lumbar puncture]] and also as vertical reference points to describe the locations of other parts of human anatomy, such as the positions of [[organ (anatomy)|organs]].
+==Other animals==
+===Variations in vertebrae===
+The general structure of vertebrae in other animals is largely the same as in humans. Individual vertebrae are composed of a centrum (body), arches protruding from the top and bottom of the centrum, and various processes projecting from the centrum and/or arches. An arch extending from the top of the centrum is called a neural arch, while the [[haemal arch]] or [[Chevron (anatomy)|chevron]] is found underneath the centrum in the caudal (tail) vertebrae of [[fish]], most [[reptile]]s, some birds, some dinosaurs and some [[mammal]]s with long tails. The vertebral processes can either give the structure rigidity, help them articulate with ribs, or serve as muscle attachment points. Common types are transverse process, diapophyses, parapophyses, and zygapophyses (both the cranial zygapophyses and the caudal zygapophyses). The centrum of the vertebra can be classified based on the fusion of its elements. In [[temnospondyli|temnospondyls]], bones such as the [[spinous process]], the pleurocentrum and the intercentrum are separate ossifications. Fused elements, however, classify a vertebra as having holospondyly.
+A vertebra can also be described in terms of the shape of the ends of the centrum. Centra with flat ends are ''acoelous'', like those in mammals. These flat ends of the centra are especially good at supporting and distributing compressive forces. ''Amphicoelous'' vertebra have centra with both ends concave. This shape is common in fish, where most motion is limited. Amphicoelous centra often are integrated with a full [[notochord]]. ''Procoelous'' vertebrae are anteriorly concave and posteriorly convex. They are found in frogs and modern reptiles. ''Opisthocoelous'' vertebrae are the opposite, possessing anterior convexity and posterior concavity. They are found in salamanders, and in some non-avian dinosaurs. ''Heterocoelous'' vertebrae have [[saddle]]-shaped articular surfaces. This type of configuration is seen in turtles that retract their necks, and birds, because it permits extensive lateral and vertical flexion motion without stretching the nerve cord too extensively or wringing it about its long axis.
+In horses, the [[Arabian horse|Arabian]] (breed) can have one less vertebrae and pair of ribs.  This anomaly disappears in foals that are the product of an Arabian and another breed of horse.<ref name=GBE73p27>Edwards, ''The Arabian'', pp. 27–28</ref>
+===Regional vertebrae===
+Vertebrae are defined by the regions of the vertebral column that they occur in, as in humans. Cervical vertebrae are those in the [[neck]] area. With the exception of the two [[sloth]] genera (''[[Choloepus]]'' and ''[[Bradypus]]'') and the [[manatee]] genus, (''[[Trichechus]]''),<ref>{{cite web|title=Sticking Their Necks out for Evolution: Why Sloths and Manatees Have Unusually Long (or Short) Necks|url=http://www.sciencedaily.com/releases/2011/05/110505212314.htm|work=May 6th 2011|publisher=Science Daily|accessdate=25 July 2013}}</ref> all mammals have seven cervical vertebrae.<ref>{{cite journal|pmid=10327647 |author=Frietson Galis |year=1999 |title=Why do almost all mammals have seven cervical vertebrae? Developmental constraints, Hox genes and Cancer |journal=Journal of experimental zoology |url=http://wwworm.biology.uh.edu/evodevo/lecture11/galis99.pdf|volume=285|issue=1|pages=19–26|doi=10.1002/(SICI)1097-010X(19990415)285:1<19::AID-JEZ3>3.0.CO;2-Z }}</ref> In other vertebrates, the number of cervical vertebrae can range from a single vertebra in [[amphibian]]s, to as many as 25 in [[swan]]s or 76 in the [[extinct]] [[plesiosaur]] ''[[Elasmosaurus]]''. The dorsal vertebrae range from the bottom of the neck to the top of the [[pelvis]]. Dorsal vertebrae attached to the [[rib]]s are called thoracic vertebrae, while those without ribs are called lumbar vertebrae. 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. When multiple sacral vertebrae are fused into a single structure, it is called the sacrum. 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]]. 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 [[chimpanzee]]s (and [[human]]s).
+===Fish and amphibians===
+[[File:Vertebre pesce 20130806 04.jpg|thumb|left|A vertebra (diameter 5 mm) of a small [[Actinopterygii|ray-finned fish]]]]
+{{see also|Fish anatomy#Vertebrae}}
+The vertebrae of [[Sarcopterygii|lobe-finned fishes]] consist of three discrete bony elements. The vertebral arch surrounds the spinal cord, and is of broadly similar form to that found in most other vertebrates. Just beneath the arch lies a small plate-like pleurocentrum, which protects the upper surface of the [[notochord]], and below that, a larger arch-shaped intercentrum to protect the lower border. Both of these structures are embedded within a single cylindrical mass of cartilage. A similar arrangement was found in the primitive [[Labyrinthodontia|Labyrinthodonts]], but in the evolutionary line that led to reptiles (and hence, also to mammals and birds), the intercentrum became partially or wholly replaced by an enlarged pleurocentrum, which in turn became the bony vertebral body.<ref name=VB/>
+In most [[Actinopterygii|ray-finned fishes]], including all [[teleost]]s, these two structures are fused with, and embedded within, a solid piece of bone superficially resembling the vertebral body of mammals. In living [[amphibian]]s, there is simply a cylindrical piece of bone below the vertebral arch, with no trace of the separate elements present in the early tetrapods.<ref name=VB/>
+In [[Chondrichthyes|cartilaginous fish]], such as [[shark]]s, the vertebrae consist of two cartilaginous tubes. The upper tube is formed from the vertebral arches, but also includes additional cartilaginous structures filling in the gaps between the vertebrae, and so enclosing the spinal cord in an essentially continuous sheath. The lower tube surrounds the notochord, and has a complex structure, often including multiple layers of [[calcification]].<ref name=VB/>
+[[Lamprey]]s have vertebral arches, but nothing resembling the vertebral bodies found in all [[higher vertebrates]]. Even the arches are discontinuous, consisting of separate pieces of arch-shaped cartilage around the spinal cord in most parts of the body, changing to long strips of cartilage above and below in the tail region. [[Hagfish]]es lack a true vertebral column, and are therefore not properly considered vertebrates, but a few tiny neural arches are present in the tail.<ref name=VB/>
+===Other vertebrates===
+[[File:718 Vertebra-en.svg|500px|thumb|Vertebral anatomy of a human spine]]
+The general structure of human vertebrae is fairly typical of that found in [[mammal]]s, [[reptile]]s, and [[bird]]s. The shape of the vertebral body does, however, vary somewhat between different groups. In mammals, such as humans, it typically has flat upper and lower surfaces, while in reptiles the anterior surface commonly has a concave socket into which the expanded convex face of the next vertebral body fits. 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. Some unusual variations include the saddle-shaped sockets between the cervical vertebrae of birds and the presence of a narrow hollow canal running down the centre of the vertebral bodies of [[gecko]]s and [[tuatara]]s, containing a remnant of the notochord.<ref name=VB/>
+Reptiles often retain the primitive intercentra, which are present as small crescent-shaped bony elements lying between the bodies of adjacent vertebrae; similar structures are often found in the caudal vertebrae of mammals. 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. These latter bones are probably [[homology (biology)|homologous]] with the [[Rib#In other animals|ventral rib]]s of fish. The number of vertebrae in the spines of reptiles is highly variable, and may be several hundred in some species of [[snake]].<ref name=VB>{{cite book |author=[[Alfred Romer|Romer, Alfred Sherwood]]|author2=Parsons, Thomas S.|year=1977 |title=The Vertebrate Body |publisher=Holt-Saunders International |location= Philadelphia, PA|pages= 161–170|isbn= 0-03-910284-X}}</ref>
+In birds, there is a variable number of cervical vertebrae, which often form the only truly flexible part of the spine. The thoracic vertebrae are partially fused, providing a solid brace for the wings during flight. The sacral vertebrae are fused with the lumbar vertebrae, and some thoracic and caudal vertebrae, to form a single structure, the '''synsacrum''', which is thus of greater relative length than the sacrum of mammals. In living birds, the remaining caudal vertebrae are fused into a further bone, the [[pygostyle]], for attachment of the tail feathers.<ref name=VB/>
+Aside from the tail, the number of vertebrae in mammals is generally fairly constant. There are almost always seven cervical vertebrae ([[sloth]]s and [[manatee]]s are among the few exceptions), followed by around twenty or so further vertebrae, divided between the thoracic and lumbar forms, depending on the number of ribs. There are generally three to five vertebrae with the sacrum, and anything up to fifty caudal vertebrae.<ref name=VB/>
+===Dinosaurs===
+The vertebral column in [[dinosaur]]s consists of the cervical (neck), dorsal (back), sacral (hips), and caudal (tail) vertebrae. Dinosaur vertebrae possess features known as [[Vertebral column#In dinosaurs|pleurocoels]], which are hollow depressions on the lateral portions of the vertebrae, which served to decrease the weight of these bones without sacrificing strength. Many researchers think that these pleurocoels were filled with air sacs, which would have further decreased weight. In [[sauropod]] dinosaurs, the largest known land vertebrates, pleurocoels may have reduced the animal's weight by over a ton in some instances, a handy evolutionary adaption in animals that grew to over 30 metres in length. In many [[hadrosaur]] and [[theropod]] dinosaurs, the caudal vertebrae were reinforced by ossified tendons. The presence of three or more sacral vertebrae, in association with the hip bones, is one of the defining characteristics of dinosaurs. The [[occipital condyle#In dinosaurs|occipital condyle]] is a structure on the posterior part of a dinosaur's skull which articulates with the first cervical vertebra.<ref>Martin, A.J. (2006). Introduction to the Study of Dinosaurs. Second Edition. Oxford, Blackwell Publishing. pg. 299-300. ISBN 1-4051-3413-5.</ref>
+==See also==
+{{Portal|Anatomy}}
+{{Commons}}
+{{Anatomy-terms}}
+* [[Low back pain]]
+* [[Neuromechanics of idiopathic scoliosis]]
+* [[Neutral spine]]
+==References==
+{{Commons category|Vertebral column}}
+{{reflist}}
+{{Authority control}}
+==External links==
+{{Wiktionary|backbone|spine}}
+* [https://web.archive.org/web/20081120164559/http://www.harms-spinesurgery.com/ZUS01E Vertebral column basics]
+* [http://www.spineuniverse.com/displayarticle.php/article1295.html Spinal Term Glossary]
+* [http://pie.med.utoronto.ca/VSpine/index.htm VIRTUAL Spine - online learning resource]
+->
 == Referències ==
 {{referències}}

Registres d'autoritat	BNF (1) GND (1) LCCN (1) NDL (1) NKC (1)
Bases d'informació	GEC (1)

Parts del cos humà
Cap	Crani o calavera · Front · Ull · Orella · Nas · Boca (Llavi · Llengua · Dent) · Mandíbula · Cara · Galta · Mentó
Coll	Clatell · Gola
Tronc	Espatlla · Esquena · Tòrax · Abdomen · Melic Aparell reproductor masculí (Penis · Escrot · Testicle) · Aparell reproductor femení (Clítoris · Vulva · Vagina) · Engonal · Maluc · Anus · Cul
Extremitat	Braç · Colze · Avantbraç · Canell · Mà · Dit (Polze · Índex · del mig · Anular · Petit) Cama · Cuixa · Genoll · Natja · Panxell · Canyella · Taló · Turmell · Peu (Hàl·lux · Planta)
Pell	Pèl · Cabells

Registres d'autoritat	BNF (1) GND (1) LCCN (1) NDL (1) NKC (1)
Bases d'informació	GEC (1)