vertebra

(vûr'tə-brə)
n., pl., -brae (-brā', -brē'), or -bras.
Any of the bones or cartilaginous segments forming the spinal column.

[Middle English, from Latin, from vertere, to turn.]

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means 'a segment of the backbone'; in the plural vertebrae (pronounced ver-ti-bree) it refers to the backbone as a whole.

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The basic unit of the vertebral column. Collectively, the vertebrae surround and protect the spinal cord and provide some type of axial support for the body. The stresses that the vertebral column must meet change somewhat from one end of the animal to the other, and also differ greatly between aquatic and terrestrial vertebrates because the problems of support and locomotion in these media are quite different. Accordingly, vertebral structure varies widely; yet all vertebrae have many features in common.

Lateral view of a human thoracic vertebra. Anterior is toward the right.

A vertebra from the thoracic region of a mammal illustrates the basic morphology well (see illustration). The ventral portion consists of a disc-shaped mass of bone known as the body or centrum. An arch of bone, the neural arch, extends dorsally from the centrum and encompasses a space, the vertebral canal, in which the spinal cord lies. The bases, or roots, of the arch are narrower than other parts so that clefts, the intervertebral foramina, lie between the arch bases of successive vertebrae. Spinal nerves pass through these foramina.

Certain muscles and ligaments attach onto the spinous process, which extends dorsally from the top of the arch, and onto a pair of transverse processes, which extend laterally from the arch. One pair of articular processes, or zygapophyses, extends forward from the neural arch, and another pair extends posteriorly. Articular processes of successive vertebrae overlap and help to hold the vertebrae together. The centra of adjacent vertebrae are also joined together by invertebral discs of fibrocartilage. Numerous ligaments interlace the vertebrae.

Ribs articulate onto the thoracic vertebrae. Typically, each mammalian rib has two articular surfaces—a terminal head and a tubercle situated a short distance distal to the head. The tubercle articulates with a facet located on the end of the transverse process; the head usually articulates intervertebrally onto the intervertebral disc and adjacent parts of the bordering centra.

In mammals different parts of the column are clearly specialized to subserve certain functions in addition to their general supportive role.

The head moves independently of the trunk, and a distinct neck region, consisting of cervical vertebrae, is present. With few exceptions all mammals from a shrew to a giraffe have seven cervical vertebrae.

Well-developed ribs, which play an important role in respiratory movements, articulate with the anterior trunk or thoracic vertebrae of mammals. The number of thoracic vertebrae varies between species but is on the order of 11 (bat) to 18 or 20 (horse). Humans have 12.

Lumbar vertebrae occupy the posterior part of the mammal trunk region. They are characterized by relatively large transverse processes to which certain of the powerful back muscles attach. Again the number of lumbar vertebrae vary between species but is on the order of 5 (bat) to 8 (whale). Humans have 5.

Correlated with the greater efficiency of terrestrial locomotion and the need for strong support for the powerful hindlegs, the number of sacral vertebrae increases during evolution from the single one of amphibians. Reptiles usually have two, and most mammals have three which are fused together, along with their embryonic rib rudiments, into a solid complex of bone called the sacrum. Humans, which are bipeds, have 5, and certain of the powerful hoofed mammals, for example, the horse, also have 5. Birds, whose hindlegs act as shock absorbers upon landing, have between 10 and 23 vertebrae fused together in their synsacrum.

The tail and caudal musculature no longer play an important role in the locomotion of most mammals (the Cetacea being a conspicuous exception), and the tail is greatly reduced in size. The spinal cord of mammals ends within the lumbar region, and only a few spinal nerves continue through the vertebrae canal into the tail. Caudal vertebrae are small and become progressively incomplete as one moves distally along the tail until only centra are left. Tail length, and hence the number of caudal vertebrae, vary widely. Some opossums have as many as 35, and humans, in which the tail is absent as an external structure, have only 3 to 5 caudal vertebrae. These form an internal coccyx to which certain anal muscles attach.

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One of the 33 bones that collectively form the vertebral column. A typical vertebra consists of a bony mass that forms the main weight-bearing component (the body or centrum), a hollow ring known as the neural or vertebral arch, and several bony processes (the transverse processes and, in some vertebrae, the neural spine, a spinous posterior extension of the neural arch). The neural arches and posterior surfaces of the vertebral bodies and intervertebral discs form a passageway for the spinal cord and blood vessels (the spinal or vertebral canal). The bony processes serve as attachment points for muscles, improving the mechanical advantage of the muscles.

Vertebra

Pl. vertebrae [L.] any of the separate segments comprising the spine (vertebral column). See also spine, vertebral.
The vertebrae support the body and provide the protective bony corridor through which the spinal cord passes. The number of bones in the vertebral column varies with the animal species and even within each species. Average numbers are given in Table 10.
The compression-resisting portion of a typical vertebra is the vertebral body, the most ventral portion. This is a cylindrical structure that is separated from the vertebral bodies in front and behind by disks of cartilage and fibrous tissue. These intervertebral disks act as cushions to spread and absorb the mechanical shock during body movements. See also slipped disk.
A semicircular arch of bone protrudes from the dorsum of each vertebral body, surrounding the spinal cord. Directly in its midline a bony projection, the spinous process, grows upward from the arch. Three pairs of outgrowths project from the arch. One of these protrudes horizontally on each side and in the thorax connects with the ribs. The remaining two form joints with the vertebrae in front and behind. The joints permit the spine to bend flexibly. The vertebrae are held firmly in place by a series of strong ligaments.

• anticlinal v. — 1. the vertebra whose spinous process is directed vertically at which point the backward slope of the cranial vertebrae changes to a forward inclination. Is usually the sixteenth thoracic vertebra in the horse.
— 2. (improperly) the diaphragmatic vertebra.
• block v. — anomalous development in which two or more vertebrae are fused.
• butterfly v. — anomalous development of a vertebra that is nearly divided in half by a longitudinal defect; caused by the persistence of the sagittal membrane remnant of the notochord. The vertebral body resembles a butterfly on ventrodorsal radiographs.
• caudal v. — coccygeal vertebrae.
• cranial v. — the segments of the skull and facial bones, regarded by some as modified vertebrae.
• v. dentata — the second cervical vertebra, or axis.
• diaphragmatic v. — the vertebra which marks the transition between those located cranially with a thoracic type of articular facet to those located caudally with a lumbar type. It is often the same vertebra as the anticlinal vertebra (above).
• false v. — those vertebrae which normally fuse with adjoining segments such as the sacral vertebrae or the human coccygeal vertebrae.
• v. magnum — the sacrum.
• odontoid v. — the second cervical vertebra, or axis.
• opisthocoelus v. — a vertebra with a concave caudal surface to the body.
• v. plana — a condition of spondylitis in which the body of the vertebra is reduced to a sclerotic disk.
• transitional v. — see transitional vertebra.
• true v. — those segments of the vertebral column that normally remain unfused throughout life: the cervical, thoracic, lumbar and coccygeal vertebrae.
• wedge-shaped v. — hemivertebra.

n

Any one of the 33 bones of the spinal or vertebral column that comprises the 7 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 4 coccygeal vertebrae.

For a list of words related to vertebra, see:

• Skeleton - vertebra: hollow bone with large central mass and fingerlike pieces of bone standing out from core

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See words rhyming with "vertebra."

  See crossword solutions for the clue Vertebra.

Dansk (Danish)
n. - ryghvirvel, rygsøjle

Nederlands (Dutch)
wervel, (mv) ruggengraat

Français (French)
n. - vertèbre

Deutsch (German)
n. - Wirbel, Wirbelsäule

Ελληνική (Greek)
n. - (ανατ.) σπόνδυλος, ραχοκόκκαλο

Italiano (Italian)
vertebra

Português (Portuguese)
n. - vértebra (f) (Anat.)

Русский (Russian)
позвонок, позвоночник

Español (Spanish)
n. - vértebra

Svenska (Swedish)
n. - ryggkota

中文（简体）(Chinese (Simplified))
脊椎骨, 椎骨

中文（繁體）(Chinese (Traditional))
n. - 脊椎骨, 椎骨

한국어 (Korean)
n. - 척추골, 척추

日本語 (Japanese)
n. - 脊椎骨, 脊柱

العربيه (Arabic)
‏(الاسم) فقرة‏

עברית (Hebrew)
n. - ‮חוליה‬

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