Vertebra

Source: Wikipedia, the free encyclopedia.
For other uses, see Vertebra (disambiguation).
Vertebra
Spinal column
Identifiers
Latinvertebra
TA98A02.2.01.001
TA21011
FMA9914
Anatomical terms of bone]

Each vertebra (pl.: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal segment and the particular species.

The basic configuration of a vertebra varies; the bone is the body, and the central part of the body is the centrum. The upper and lower surfaces of the vertebra body give attachment to the

articulate. These foramina are the entry and exit conduits for the spinal nerves. The body of the vertebra and the vertebral arch form the vertebral foramen, the larger, central opening that accommodates the spinal canal, which encloses and protects the spinal cord
.

Vertebrae articulate with each other to give strength and flexibility to the spinal column, and the shape at their back and front aspects determines the range of movement. Structurally, vertebrae are essentially alike across the vertebrate species, with the greatest difference seen between an aquatic animal and other vertebrate animals. As such, vertebrates take their name from the vertebrae that compose the vertebral column.

Structure

In the human vertebral column, the size of the vertebrae varies according to placement in the vertebral column, spinal loading, posture and pathology. Along the length of the spine, the vertebrae change to accommodate different needs related to stress and mobility.[1] Each vertebra is an irregular bone.

Side view of vertebrae

A typical vertebra has a body (vertebral body), which consists of a large anterior middle portion called the centrum (vertebral centrum, plural centra) and a posterior vertebral arch,

collagen fibers of the disc. They also act as a semi-permeable interface for the exchange of water and solutes.[5]

Anatomy of a vertebra

The vertebral arch is formed by pedicles and laminae. Two pedicles extend from the sides of the vertebral body to join the body to the arch. The pedicles are short thick processes that extend, one from each side, posteriorly, from the junctions of the posteriolateral surfaces of the centrum, on its upper surface. From each pedicle a broad plate, a lamina, projects backward and medially to join and complete the vertebral arch and form the posterior border of the vertebral foramen, which completes the triangle of the vertebral foramen.

intervertebral foramina
. The foramina allow the entry and exit of the spinal nerves from each vertebra, together with associated blood vessels. The articulating vertebrae provide a strong pillar of support for the body.

Processes

There are seven processes projecting from the vertebra:

  • one spinous process
  • two transverse processes
  • four
    articular processes

A major part of a vertebra is a backward extending spinous process (sometimes called the neural spine) which projects centrally.

caudally from the junction of the laminae.[7] The spinous process serves to attach muscles and ligaments
.

The two transverse processes, one on each side of the vertebral body, project laterally from either side at the point where the lamina joins the

lumbar vertebra is also sometimes called the costal[9][10] or costiform process[11] because it corresponds to a rudimentary rib (costa) which, as opposed to the thorax, is not developed in the lumbar region.[11][12]

There are superior and inferior articular facet joints on each side of the vertebra, which serve to restrict the range of movement possible. These facets are joined by a thin portion of the vertebral arch called the pars interarticularis.

Regional variation

Segments of the vertebrae

Vertebrae take their names from the regions of the vertebral column that they occupy. There are usually thirty-three vertebrae in the human vertebral column — seven

coccygeal vertebrae, forming the coccyx. Excluding rare deviations, the total number of vertebrae ranges from 32 to 35.[13] In about 10% of people, both the total number of pre-sacral vertebrae and the number of vertebrae in individual parts of the spine can vary.[14][15] The most frequent deviations are eleven (rarely thirteen) thoracic vertebrae, four or six lumbar vertebrae and three or five coccygeal vertebrae (rarely up to seven).[15]

The regional vertebrae increase in size as they progress downward but become smaller in the coccyx.

Cervical

Main article: Cervical vertebrae
A typical cervical vertebra

There are seven

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 disc of the spinal column.

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 is not bifurcated, and is substantially longer than that of the other cervical spinous processes).[16]

The atlas differs from the other vertebrae in that it has no body and no spinous process. It has instead a ring-like form, having an anterior and a posterior arch and two lateral masses. At the outside centre points of both arches there is a tubercle, an anterior tubercle and a posterior tubercle, for the attachment of muscles. The front surface of the anterior arch is convex and its anterior tubercle gives attachment to the

skull. On the under surface is a facet for articulation with the dens
of the axis.

Specific to the cervical vertebra is the transverse foramen (also known as foramen transversarium). This is an opening on each of the transverse processes which gives passage to the vertebral artery and vein and a sympathetic nerve plexus. On the cervical vertebrae other than the atlas, the anterior and posterior tubercles are on either side of the transverse foramen on each transverse process. The anterior tubercle on the sixth cervical vertebra is called the carotid tubercle because it separates the carotid artery from the vertebral artery.

There is a hook-shaped uncinate process on the side edges of the top surface of the bodies of the third to the seventh cervical vertebrae and of the first thoracic vertebra. Together with the vertebral disc, this uncinate process prevents a vertebra from sliding backward off the vertebra below it and limits lateral flexion (side-bending). Luschka's joints involve the vertebral uncinate processes.

The spinous process on C7 is distinctively long and gives the name

vertebra prominens to this vertebra. Also a cervical rib can develop from C7 as an anatomical variation
.

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

Thoracic

Main article: Thoracic vertebrae
A typical thoracic vertebra

The twelve thoracic vertebrae 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 movement. 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-posteriorly as they are in the transverse dimension. Vertebral foramina are roughly circular in shape.

The top surface of the first thoracic vertebra has a hook-shaped uncinate process, just like the cervical vertebrae.

The thoracolumbar division refers to the thoracic and lumbar vertebrae together, and sometimes also their surrounding areas.

The thoracic vertebrae attach to ribs and so have articular facets specific to them; these are the superior, transverse and inferior costal facets. As the vertebrae progress down the spine they increase in size to match up with the adjoining lumbar section.

Lumbar

Main article: Lumbar vertebrae
Lumbar vertebra showing mammillary processes
A typical lumbar vertebra

The five lumbar vertebrae are the largest of the vertebrae, their robust construction being necessary for supporting greater weight than the other vertebrae. They allow significant flexion, extension and moderate lateral flexion (side-bending). The discs between these vertebrae create a natural lumbar lordosis (a spinal curvature that is concave posteriorly).[citation needed] This is due to the difference in thickness between the front and back parts of the intervertebral discs.

The lumbar vertebrae are located between the ribcage and the pelvis and are the largest of the vertebrae. The pedicles are strong, as are the laminae, and the spinous process is thick and broad. The vertebral foramen is large and triangular. The transverse processes are long and narrow and three tubercles can be seen on them. These are a lateral costiform process, a mammillary process and an accessory process.[17] The superior, or upper tubercle is the mammillary process which connects with the superior articular process. The multifidus muscle attaches to the mammillary process and this muscle extends through the length of the vertebral column, giving support. The inferior, or lower tubercle is the accessory process and this is found at the back part of the base of the transverse process. The term lumbosacral is often used to refer to the lumbar and sacral vertebrae together, and sometimes includes their surrounding areas.

Sacral

Sacrum
Main article: Sacrum

There are five sacral vertebrae (S1–S5) which are fused in maturity, into one large bone, the

hips
.

Coccygeal

Main article: Coccyx

The last three to five coccygeal vertebrae (but usually four) (Co1–Co5) make up the tailbone or coccyx.[19] There are no intervertebral discs.

Development

Development of vertebrae
Development of vertebrae

vertebral arch. Other cells move distally to the costal processes of thoracic vertebrae to form the ribs.[20]

Function

Functions of vertebrae include:

  1. Support of the vertebrae function in the skeletomuscular system by forming the vertebral column to support the body
  2. Protection. Vertebrae contain a vertebral foramen for the passage of the spinal canal and its enclosed spinal cord and covering meninges. They also afford sturdy protection for the spinal cord. The upper and lower surfaces of the centrum are flattened and rough in order to give attachment to the intervertebral discs.
  3. Movement. The vertebrae also provide the openings, the intervertebral foramina which allow the entry and exit of the
    spinal nerves. Similarly to the surfaces of the centrum, the upper and lower surfaces of the fronts of the laminae are flattened and rough to give attachment to the ligamenta flava
    . Working together in the vertebral column their sections provide controlled movement and flexibility.
  4. Feeding of the intervertebral discs through the reflex (hyaline ligament) plate that separates the cancellous bone of the vertebral body from each disk
  • The spinal cord nested in the vertebral column.
    The spinal cord nested in the vertebral column.
  • Vertebral joint
    Vertebral joint
  • Costovertebral joint
    Costovertebral joint
  • A facet joint between the superior and inferior articular processes (labeled at top and bottom).
    A facet joint between the superior and inferior articular processes (labeled at top and bottom).

Clinical significance

There are a number of

Block vertebrae where some vertebrae have become fused can cause problems. Spina bifida
can result from the incomplete formation of the vertebral arch.

Spondylolysis is a defect in the pars interarticularis of the vertebral arch. In most cases this occurs in the lowest of the lumbar vertebrae (L5), but may also occur in the other lumbar vertebrae, as well as in the thoracic vertebrae.

minimally-invasive endoscopic procedure called Tessys method
.

A laminectomy is a surgical operation to remove the laminae in order to access the spinal canal.[21] The removal of just part of a lamina is called a laminotomy.

A

pinched nerve caused by pressure from a disc, vertebra or scar tissue might be remedied by a foraminotomy to broaden the intervertebral foramina and relieve pressure. It can also be caused by a foramina stenosis, a narrowing of the nerve opening, as a result of arthritis
.

Another condition is spondylolisthesis when one vertebra slips forward onto another. The reverse of this condition is retrolisthesis where one vertebra slips backward onto another.

The vertebral pedicle is often used as a radiographic marker and entry point in

kyphoplasty, and spinal fusion
procedures.

The arcuate foramen is a common anatomical variation more frequently seen in females. It is a bony bridge found on the first cervical vertebra, the atlas where it covers the groove for the vertebral artery.[22]

Degenerative disc disease is a condition usually associated with ageing in which one or more discs degenerate. This can often be a painfree condition but can also be very painful.

Non-humans

Regions of vertebrae in the goat

In other animals, the vertebrae take the same regional names except for the coccygeal – in animals with tails, the separate vertebrae are usually called the caudal vertebrae.

extinct Dimetrodon and Spinosaurus
, where they form a sailback or finback.

Vertebrae with saddle-shaped articular surfaces on their bodies, called "heterocoelous", allow vertebrae to flex both vertically and horizontally while preventing twisting motions. Such vertebrae are found in the necks of birds and some turtles.[23]

An example of procoelous vertebrae dissected from a rattlesnake.

"Procoelous" vertebrae feature a spherical protrusion extending from the caudal end of the centrum of one vertebra that fits into a concave socket on the cranial end of the centrum of an adjacent vertebra.

anterior vertebra acts as the ball to the socket of a caudal vertebra.[25] This type of connection permits a wide range of motion in most directions, while still protecting the underlying nerve cord. The central point of rotation is located at the midline of each centrum, and therefore flexion of the muscle surrounding the vertebral column does not lead to an opening between vertebrae.[27]

In many species, though not in mammals, the cervical vertebrae bear ribs. In many groups, such as

amniotes. In the whale, the cervical vertebrae are typically fused, an adaptation trading flexibility for stability during swimming.[28][29] All mammals except manatees and sloths have seven cervical vertebrae, whatever the length of the neck.[30] This includes seemingly unlikely animals such as the giraffe, the camel, and the blue whale, for example. Birds
usually have more cervical vertebrae with most having a highly flexible neck consisting of 13–25 vertebrae.

In all mammals, the thoracic vertebrae are connected to

cetacean.[33]

There are fewer lumbar vertebrae in chimpanzees and gorillas, which have three in contrast to the five in the genus Homo. This reduction in number gives an inability of the lumbar spine to lordose but gives an anatomy that favours vertical climbing, and hanging ability more suited to feeding locations in high-canopied regions.[34] The bonobo differs by having four lumbar vertebrae.

Caudal vertebrae are the bones that make up the tails of vertebrates.[35]
They range in number from a few to fifty, depending on the length of the animal's tail. In humans and other tailless
coccygeal vertebrae, number from three to five and are fused into the coccyx.[36]

Additional images

  • Vertebral arches of three thoracic vertebrae
    Vertebral arches of three thoracic vertebrae
  • Costovertebral joints seen from the front
    Costovertebral joints seen from the front
  • Lower thoracic and upper lumbar vertebrae seen from the side
    Lower thoracic and upper lumbar vertebrae seen from the side
  • Cervical vertebrae seen from the back
    Cervical vertebrae seen from the back
  • Vertebrae anatomy

See also

References

Public domain This article incorporates text in the public domain from page 96 of the 20th edition of Gray's Anatomy (1918)

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  10. ^ Latin costa refers to either a "rib" or "side" of the body. (Diab (1999), p 76)
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  12. ^ Heinz Feneis, Wolfgang Dauber (2000) Pocket Atlas of Human Anatomy: Based on the International Nomenclature p. 2
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