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Information about Vertebra

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A diagram of a thoracic vertebra. Notice the articulations for the ribs
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Different regions of the vertebral column




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The Vertebral Column (singular: vertebra) are the individual irregular bones that make up the spinal column (aka ischis) — a flexuous and flexible column. There are normally thirty-three (33) vertebrae in humans, including the five that are fused to form the sacrum (the others are separated by intervertebral discs) and the four coccygeal bones which form the tailbone. The upper three regions comprise the remaining 24, and are grouped under the names cervical (7 vertebrae), thoracic (12 vertebrae) and lumbar (5 vertebrae), according to the regions they occupy. This number is sometimes increased by an additional vertebra in one region, or it may be diminished in one region, the deficiency often being supplied by an additional vertebra in another. The number of cervical vertebrae is, however, very rarely increased or diminished.

With the exception of the first and second cervical, the true or movable vertebrae (the upper three regions) present certain common characteristics which are best studied by examining one from the middle of the thoracic region.

General structure

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Oblique view of cervical vertebrae
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), while 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.

Regions

Cervical

Note: For more detailed information, see Cervical vertebrae

These are generally small and delicate. Their spinous processes are short (with the exception of C2 and C7, which have palpable spinous processes), and often split. Numbered top-to-bottom from C1-C7, atlas (C1) and axis (C2), are the vertebrae that allow the neck and head so much movement. For the most part, 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.

Thoracic

Note: For more detailed information, see Thoracic vertebrae

Their spinous 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.

Lumbar

Note: For more detailed information, see Lumbar vertebrae

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

Sacral

Note: For more detailed information, see Sacral vertebrae

There are 5 vertebrae (S1-S5). They are fused in maturity, with no intervertebral discs.

Coccygeal

Note: For more detailed information, see Coccygeal vertebrae

There are 3-5 vertebrae (Co1-Co5), again fused, with no intervertebral discs. Many animals have a greater number of 'tail vertebrae' and, in animals, they are more commonly known as caudal vertebrae. Pain at the coccyx (tailbone) is known as coccydynia.

Development

During the fourth week of embryonic development, the sclerotomes shift their position to surround the spinal cord and the notochord. The sclerotome is made of mesoderm and originates from the ventromedial part of the somites. 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 annulus 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.

There are various defects associated with vertebral development. Scoliosis can result from improper fusion of the vertebrae. In Klippel-Feil anomaly patients have two or more cervical vertebrae that are fused together, along with other associated birth defects. One of the most serious defects is failure of the vertebral arches to fuse. This results in a condition called spina bifida. There are several variations of spina bifida that reflect the severity of the defect.

Footnotes

1. ^ Anatomy Compendium (Godfried Roomans and Anca Dragomir)

References

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Vertebral column and spinal cord
Vertebrae cervical: C1 (Atlas) • C2 (Axis) • C3 • C4 • C5 • C6 • C7 (Vertebra prominens) thoracic: T1 • T2 • T3 • T4 • T5 • T6 • T7 • T8 • T9 • T10 • T11 • T12 lumbar: L1 • L2 • L3 • L4 • L5 sacral: S1 • S2 • S3 • S4 • S5 coccygeal: Co1 • Co2 • Co3 • (Co4) • (Co5)
Spinal nerves cervical: C1 • C2 • C3 • C4 • C5 • C6 • C7 • C8 thoracic: T1 • T2 • T3 • T4 • T5 • T6 • T7 • T8 • T9 • T10 • T11 • T12 lumbar: L1 • L2 • L3 • L4 • L5 sacral: S1 • S2 • S3 • S4 • S5 coccygeal: Co






The irregular bones are such as, from their peculiar form, cannot be grouped as long bone, short bone, flat bone or sesamoid bone. Irregular bones serve some unique purpose in the body of combining: (1) protection of nervous tissue (such as the vertebrae protect the spinal cord),
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The sacrum is a large, triangular bone at the base of the spine and at the upper and back part of the pelvic cavity, where it is inserted like a wedge between the two hip bones.
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Intervertebral discs (or intervertebral fibrocartilage) lie between adjacent vertebrae in the spine. Each disc forms a cartilaginous joint to allow slight movement of the vertebrae, and acts as a ligament to hold the vertebrae together.
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The coccyx (pronounced kok-siks) (Latin: os coccygis), commonly referred to as the tailbone, is the final segment of the human vertebral column, of four fused vertebrae (the coccygeal vertebrae) below the sacrum.
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Bones are rigid organs that form part of the endoskeleton of vertebrates. They function to move, support, and protect the various organs of the body, produce red and white blood cells and store minerals.
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The body is the largest part of a vertebra, and is more or less cylindrical in shape.

Its upper and lower surfaces are flattened and rough, and give attachment to the intervertebral fibrocartilages, and each presents a rim around its circumference.
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The vertebral arch (or neural arch) is the posterior part of a vertebra.

It consists of a pair of pedicles and a pair of laminae, and supports seven processes:
  • four articular processes
  • two transverse processes
  • one spinous process


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In a typical vertebra, the vertebral foramen is the foramen formed by the anterior segment (the body), and the posterior part, the vertebral arch.

The vertebral foramen begins at cervical vertebrae #1 (atlas) and continues inferior to lumbar vertebrae #5.
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The pedicles (from Latin pediculus, "small foot") are two short, thick processes, which project backward, one on either side, from the upper part of the body, at the junction of its posterior and lateral surfaces.
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The laminæ are two broad plates directed backward and medially from the pedicles.

They fuse in the middle line posteriorly, and so complete the posterior boundary of the vertebral foramen.
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In anatomy, a process (Latin: processus) is a projection or outgrowth of tissue from a larger body.

Examples

Examples of processes include:
  • the mastoid process
  • the xyphoid process

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head of an animal is the rostral part (from anatomical position) that usually comprises the brain, eyes, ears, nose, and mouth (all of which aid in various sensory functions, such as sight, hearing, smell, and taste).
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Trunk may be:
  • Trunk (botany), the main structural member of a tree.
  • Trunk (structural), a chute or conduit, or a watertight shaft connecting two or more decks.
  • Trunk (luggage), a large case.

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spinal chord is a thin, tubular bundle of nerves that is an extension of the central nervous system from the brain and is enclosed in and protected by the bony vertebral column.
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intervertebral foramina (singular: foramen; also called neural foramina). The foramen allows for the passage of the spinal nerve root, dorsal root ganglion, the spinal artery of the segmental artery, communicating veins between the internal and external plexuses,
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The transverse processes of a vertebra, two in number, project one at either side from the point where the lamina joins the pedicle, between the superior and inferior articular processes. They serve for the attachment of muscles and ligaments.
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The spinous process of a vertebra is directed backward and downward from the junction of the laminae (in humans), and serves for the attachment of muscles and ligaments. In animals without an erect stance, the process points upward and may slant forward or backward.
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A zygapophysial joint (zygapophyseal, or facet joint) is a synovial joint between the superior articular process of one (lower) vertebra and the inferior articular process of the adjacent (higher) vertebra. There are two facet joints in each vertebral motion segment.
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The pars interarticularis, sometimes referred to as pars for short, is the part of vertebra located between the inferior and superior articular processes of the facet joint.[1] In the transverse plane, it lies between the lamina and pedicle.
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In vertebrates, cervical vertebrae (singular: vertebra) are those vertebrae immediately behind (caudal to) the skull.

Variation among species

In some species, some parts of the skull may be composed of vertebra-like elements, e.g.
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In anatomy, the atlas (C1) is the topmost (first) cervical vertebra of the spine.

It is named for the Atlas of mythology, because it supports the globe of the head.
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axis (from Latin axis, "axle") or epistropheus.

It forms the pivot upon which the first cervical vertebra (the atlas), which carries the head, rotates.
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The neck is the part of the body on many limbed vertebrates that distinguishes the head from the torso or trunk.

Anatomy of the human neck

Bony anatomy: The cervical spine

The cervical portion of the human spine
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head of an animal is the rostral part (from anatomical position) that usually comprises the brain, eyes, ears, nose, and mouth (all of which aid in various sensory functions, such as sight, hearing, smell, and taste).
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The Atlanto-occipital joint (articulation between the atlas and the occipital bone) consists of a pair of condyloid joints.

Ligaments

The ligaments connecting the bones are:
  • Two Articular capsules
  • Posterior atlantoöccipital membrane

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skull is a bony structure found in many animals which serves as the general framework for the head. The skull supports the structures of the face and protects the head against injury.

The skull can be subdivided into two parts: the cranium and the mandible.
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The Atlanto-axial joint (articulation of the atlas with the axis) is of a complicated nature, comprising no fewer than four distinct joints.

There is a pivot articulation between the odontoid process of the axis and the ring formed by the anterior arch and the
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Mammalia
Linnaeus, 1758

Subclasses & Infraclasses
  • Subclass †Allotheria*
  • Subclass Prototheria
  • Subclass Theria

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worldwide view of the subject.
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Manatee

Antillean Manatee


Scientific classification

Kingdom: Animalia
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Folivora
Delsuc et al, 2001

Families

Megalonychidae
Bradypodidae
†Rathymotheriidae
†Scelidotheriidae
†Mylodontidae
†Orophodontidae
†Megatheriidae

Sloths
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