Human vertebral column

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This article is about features specific to the human vertebral column. For information about the vertebral column, see Vertebral column. For other uses, see Vertebra (anatomy).
Vertebral column
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The human vertebral column
Latin Columnar vertebralis
Anatomical terminology

The human vertebral column (Latin: columna vertebralis) is the backbone or spine, consisting of twenty-four articulating vertebrae, and nine fused vertebrae in the sacrum and the coccyx.[1] The vertebrae in the column are separated from each other by intervertebral discs. It houses and protects the spinal cord in its spinal canal.

There are normally thirty-three vertebrae; the upper twenty-four are articulating and separated from each other by intervertebral discs, and the lower nine are fused, 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.[2]

All the articulating vertebrae are essentially alike but there are some variations between those in different regions.

Regions[edit]

Numbering order of the vertebrae of the human spinal column

There are a total of 33 vertebrae in the vertebral column, if assuming 4 coccygeal vertebrae.

The individual vertebrae, named according to region and position, from superior to inferior, are:

  • Cervical: 7 vertebrae (C1–C7)
  • Thoracic: 12 vertebrae (T1–T12)
  • Lumbar: 5 vertebrae (L1–L5)
  • Sacral: 5 (fused) vertebrae (S1–S5)
  • Coccygeal: 4 (3–5) (fused) vertebrae (Tailbone)

Cervical[edit]

Main article: Cervical vertebrae

There are seven cervical bones (but eight cervical spinal nerves) and these bones are, in general, small and delicate. Their spinous processes are short (with the exception of C2 and C7, which have palpable spinous processes). Numbered top-to-bottom from C1-C7, atlas (C1) and axis (C2), are the vertebrae that allow the neck and head so much movement. The atlanto-occipital joint allows the skull to move up and down, while the atlanto-axial joint allows the upper neck to twist left and right. The axis also sits upon the first intervertebral disk of the spinal column. All mammals except manatees and sloths have seven cervical vertebrae, whatever the length of the neck.[3] This includes seemingly unlikely animals such as the giraffe, the camel, and the blue whale, for example.

Cervical vertebrae possess transverse foramina to allow for the vertebral arteries to pass through on their way to the foramen magnum to end in the circle of Willis. These are the smallest, lightest vertebrae and the vertebral foramina are triangular in shape. The spinous processes are short and often bifurcated (the spinous process of C7, however, is not bifurcated, and is substantially longer than that of the other cervical spinous processes).

The term cervicothoracic is often used to refer to the cervical and thoracic vertebrae together, and sometimes also their surrounding areas.

Thoracic[edit]

Main article: Thoracic vertebrae

The twelve thoracic bones and their transverse processes have surfaces that articulate with the ribs. Some rotation can occur between the thoracic vertebrae, but their connection with the rib cage prevents much flexion or other excursion. They may also be known as 'dorsal vertebrae', in the human context.

The vertebral bodies are roughly heart-shaped and are about as wide anterio-posterioly as they are in the transverse dimension. Vertebral foramina are roughly circular in shape.

The term thoracolumbar is sometimes used to refer to the thoracic and lumbar vertebrae together, and sometimes also their surrounding areas.

Lumbar[edit]

Main article: Lumbar vertebrae

These five vertebrae are very robust in construction, as they must support more weight than other vertebrae. They allow significant flexion, extension and moderate lateral flexion (sidebending). The discs between these vertebrae create a lumbar lordosis (curvature that is concave posteriorly) in the human spine.[citation needed]

The term lumbosacral is often used to refer to the lumbar and sacral vertebrae together, and sometimes also their surrounding areas.

Sacral[edit]

Main article: Sacrum

There are five vertebrae (S1-S5) which are fused in maturity, into one large bone the sacrum with no intervertebral discs.[4]

Coccygeal[edit]

Main article: Coccyx

There are three to five, but usually four coccygeal vertebrae (Co1-Co5) which make up the tailbone. There are no intervertebral discs.

Structure[edit]

Main article: Vertebra (anatomy)
Vertebral anatomy
Vertebral joint

A typical vertebra consists of two essential parts: an anterior (front) segment, which is the vertebral body; and a posterior part – the vertebral (neural) arch – which encloses the vertebral 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.

When the vertebrae are articulated with each other, the bodies form a strong pillar for the support of the head and trunk, and the vertebral foramina constitute a canal for the protection of the medulla spinalis (spinal cord). In between every pair of vertebrae are two apertures, the intervertebral foramina, one on either side, for the transmission of the spinal nerves and vessels.

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.

Superior and inferior articular facets on each vertebra act to restrict the range of movement possible. These facets are joined by a thin portion of the neural arch called the pars interarticularis.

Curves[edit]

Curves of spine
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. Furthermore, C7 is easily localized as a prominence at the lower part of the neck.[5]

Viewed laterally the vertebral column presents several curves, which correspond to the different regions of the column, and are called cervical, thoracic, lumbar, and sacral.

The cervical curve, convex forward, begins at the second cervical vertebra the axis at the apex of the odontoid process known as the dens, and ends at the middle of the second thoracic vertebra; it is the least marked of all the curves.

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.

The thoracic and sacral 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 at twelve or eighteen months, when the child begins to walk.

Surfaces[edit]

Anterior surface[edit]

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.

Posterior surface[edit]

The posterior surface of 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 vertebral grooves 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.

Lateral surfaces[edit]

The lateral surfaces are separated from the posterior surface by the articular processes in the cervical and lumbar regions, and by the transverse processes in the thoracic region. They present, in back, the sides of the bodies of the vertebrae, marked in the thoracic region 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.

Spinal canal[edit]

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]

Development[edit]

The vertebrae may be used as vertical reference points to describe the locations of the organs of the trunk, such as with the transpyloric line (seen at body of L1). If not else specified, it is usually the middle of the vertebral body that is used as reference, although the palpable spinous processes may be located considerably lower.

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 (including some of the skull, vertebrae and ribs) muscle and skin. Somatogenesis 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 subvidided 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.[6] 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.

Clinical significance[edit]

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.[7] 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.

Pain at the coccyx (tailbone) is known as coccydynia.[8]

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.

Additional images[edit]

See also[edit]

This article uses anatomical terminology; for an overview, see anatomical terminology.

References[edit]

  1. ^ Dorland's (2012). Dorland's Illustrated Medical Dctionary (32nd ed.). Elsevier Saunders. p. 2050. ISBN 978-1-4160-6257-8. 
  2. ^ Gray, Henry (1977). Gray's Anatomy. New York: Crown Publishers, Inc. p. 34. 
  3. ^ books.google.com
  4. ^ Drake et al, Gray's Anatomy for Students, Churchill Livingstone/Elsevier (2010), 2nd edition, chapter 2
  5. ^ Anatomy Compendium (Godfried Roomans and Anca Dragomir)
  6. ^ Somites, Spinal Ganglia, and Centra
  7. ^ Dorland's (2012). Dorland's Illustrated Medical Dctionary (32nd ed.). Elsevier Saunders. p. 1748. ISBN 978-1-4160-6257-8. 
  8. ^ Patel, R; Appannagari, A; Whang, P.G. (May 2008). "Coccydynia". Current Reviews in Musculoskeletal Medicine 1 (3-4): 223–226. doi:10.1007/s12178-008-9028-1. PMID 19468909. 

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