Thoracic vertebrae
Overview
 
In human anatomy, twelve thoracic vertebrae compose the middle segment of the vertebral column
Vertebral column
In human anatomy, the vertebral column is a column usually consisting of 24 articulating vertebrae, and 9 fused vertebrae in the sacrum and the coccyx. It is situated in the dorsal aspect of the torso, separated by intervertebral discs...

, between the cervical vertebrae
Cervical vertebrae
In vertebrates, cervical vertebrae are those vertebrae immediately inferior to the skull.Thoracic vertebrae in all mammalian species are defined as those vertebrae that also carry a pair of ribs, and lie caudal to the cervical vertebrae. Further caudally follow the lumbar vertebrae, which also...

 and the lumbar vertebrae
Lumbar vertebrae
The lumbar vertebrae are the largest segments of the movable part of the vertebral column, and are characterized by the absence of the foramen transversarium within the transverse process, and by the absence of facets on the sides of the body...

. They are intermediate in size between those of the cervical and lumbar regions; they increase in size as one proceeds down the spine, the upper vertebrae being much smaller than those in the lower part of the region. They are distinguished by the presence of facets on the sides of the bodies for articulation with the heads of the ribs, and facets on the transverse processes of all, except the eleventh and twelfth, for articulation with the tubercles of the rib
Rib
In vertebrate anatomy, ribs are the long curved bones which form the rib cage. In most vertebrates, ribs surround the chest, enabling the lungs to expand and thus facilitate breathing by expanding the chest cavity. They serve to protect the lungs, heart, and other internal organs of the thorax...

s.
Encyclopedia
In human anatomy, twelve thoracic vertebrae compose the middle segment of the vertebral column
Vertebral column
In human anatomy, the vertebral column is a column usually consisting of 24 articulating vertebrae, and 9 fused vertebrae in the sacrum and the coccyx. It is situated in the dorsal aspect of the torso, separated by intervertebral discs...

, between the cervical vertebrae
Cervical vertebrae
In vertebrates, cervical vertebrae are those vertebrae immediately inferior to the skull.Thoracic vertebrae in all mammalian species are defined as those vertebrae that also carry a pair of ribs, and lie caudal to the cervical vertebrae. Further caudally follow the lumbar vertebrae, which also...

 and the lumbar vertebrae
Lumbar vertebrae
The lumbar vertebrae are the largest segments of the movable part of the vertebral column, and are characterized by the absence of the foramen transversarium within the transverse process, and by the absence of facets on the sides of the body...

. They are intermediate in size between those of the cervical and lumbar regions; they increase in size as one proceeds down the spine, the upper vertebrae being much smaller than those in the lower part of the region. They are distinguished by the presence of facets on the sides of the bodies for articulation with the heads of the ribs, and facets on the transverse processes of all, except the eleventh and twelfth, for articulation with the tubercles of the rib
Rib
In vertebrate anatomy, ribs are the long curved bones which form the rib cage. In most vertebrates, ribs surround the chest, enabling the lungs to expand and thus facilitate breathing by expanding the chest cavity. They serve to protect the lungs, heart, and other internal organs of the thorax...

s. The cervical vertebrae runs into the cranium.

By convention, the human thoracic vertebrae are numbered, with the first one (T1) located closest to the skull and higher numbered vertebrae (T2-T12) proceeding away from the skull and down the spine.

General characteristics

These are the general characteristics of the second through eighth thoracic vertebrae.
The first and ninth through twelfth vertebrae contain certain peculiarities, and are detailed below.

The bodies
Body of vertebra
The body is the largest part of a vertebra, and is more or less cylindrical in shape. For vertebrates other than humans, this structure is usually called a centrum....

in the middle of the thoracic region are heart-shaped, and as broad in the antero-posterior as in the transverse direction. At the ends of the thoracic region they resemble respectively those of the cervical and lumbar vertebrae. They are slightly thicker behind than in front, flat above and below, convex from side to side in front, deeply concave behind, and slightly constricted laterally and in front. They present, on either side, two costal demi-facets, one above, near the root of the pedicle, the other below, in front of the inferior vertebral notch; these are covered with cartilage in the fresh state, and, when the vertebrae are articulated with one another, form, with the intervening intervertebral fibrocartilages, oval surfaces for the reception of the heads of the ribs.

The pedicles
Pedicle of vertebral arch
The pedicles are two short, thick processes, which project dorsally, one on either side, from the superior part of the vertebral body at the junction of its posterior and lateral surfaces. They connect the body of the spinal vertebra to the arch...

are directed backward and slightly upward, and the inferior vertebral notches are of large size, and deeper than in any other region of the vertebral column.

The laminae
Lamina of the vertebral arch
The laminæ are two broad plates, extending dorsally and medially from the pedicles, fusing to complete the roof of the vertebral arch.Their upper borders and the lower parts of their anterior surfaces are rough for the attachment of the ligamenta flava....

are broad, thick, and imbricated — that is to say, they overlap those of subjacent vertebrae like tiles on a roof.

The vertebral foramen
Vertebral foramen
In a typical vertebra, the vertebral foramen is the foramen formed by the anterior segment , and the posterior part, the vertebral arch....

is small, and of a circular form.

The spinous process
Spinous process
The spinous process of a vertebra is directed backward and downward from the junction of the laminae , 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...

is long, triangular on coronal section, directed obliquely downward, and ends in a tuberculated extremity. These processes overlap from the fifth to the eighth, but are less oblique in direction above and below.

The superior articular processes are thin plates of bone projecting upward from the junctions of the pedicles and laminae; their articular facets are practically flat, and are directed backward and a little lateralward and upward.

The inferior articular processes are fused to a considerable extent with the laminae, and project but slightly beyond their lower borders; their facets are directed forward and a little medialward and downward.

The transverse processes arise from the arch behind the superior articular processes and pedicles; they are thick, strong, and of considerable length, directed obliquely backward and lateralward, and each ends in a clubbed extremity, on the front of which is a small, concave surface, for articulation with the tubercle of a rib. *

Individual thoracic vertebrae

First thoracic vertebra

The first thoracic vertebra has, on either side of the body, an entire articular facet for the head of the first rib, and a demi-facet for the upper half of the head of the second rib.

The body is like that of a cervical vertebra, being broad tconcave, and lipped on either side.

The superior articular surfaces are directed upward and backward; the spinous process is thick, long, and almost horizontal.

The transverse processes are long, and the upper vertebral notches are deeper than those of the other thoracic vertebrae.

The thoracic spinal nerve 1
Thoracic spinal nerve 1
The thoracic spinal nerve 1 is a spinal nerve of the thoracic segment..It originates from the spinal column from below the thoracic vertebra 1 ....

 (T1) passes out underneath it.

Fourth thoracic vertebra

The fourth thoracic vertebra, together with the fifth, is at the same level as the sternal angle
Sternal angle
The sternal angle or 'angle of Louis', from the Latin angulus Ludovici is the anterior angle formed by the junction of the manubrium and the body of the sternum in the form of a secondary cartilaginous joint . This is also called the manubriosternal joint or Angle of Louis...

.

The thoracic spinal nerve 4
Thoracic spinal nerve 4
The thoracic spinal nerve 4 is a spinal nerve of the thoracic segment..It originates from the spinal column from below the thoracic vertebra 4 ....

 (T4) passes out underneath it.

Fifth thoracic vertebra

The fifth thoracic vertebra, together with the fourth, is at the same level as the sternal angle
Sternal angle
The sternal angle or 'angle of Louis', from the Latin angulus Ludovici is the anterior angle formed by the junction of the manubrium and the body of the sternum in the form of a secondary cartilaginous joint . This is also called the manubriosternal joint or Angle of Louis...

.

The thoracic spinal nerve 5
Thoracic spinal nerve 5
The thoracic spinal nerve 5 is a spinal nerve of the thoracic segment..It originates from the spinal column from below the thoracic vertebra 5 ....

 (T5) passes out underneath it.

Eighth thoracic vertebra

The eighth thoracic vertebra is, together with the ninth thoracis vertebra, at the same level as the xiphoid process
Xiphoid process
The xiphoid process, or xiphisternum or metasternum, is a small cartilaginous process of the lower part of the sternum which is usually ossified in the adult human. By age 15 to 29, the xiphoid usually fuses to the body of the sternum with a fibrous joint. Unlike the synovial articulation of major...

.

The thoracic spinal nerve 8
Thoracic spinal nerve 8
The thoracic spinal nerve 8 is a spinal nerve of the thoracic segment..It originates from the spinal column from below the thoracic vertebra 8 ....

 (T8) passes out underneath it.

Ninth thoracic vertebra

The ninth thoracic vertebra may have no demi-facets below. In some subjects however, it has two demi-facets on either side; when this occurs the tenth doesn't have facets but demi-facets at the upper part.

The thoracic spinal nerve 9
Thoracic spinal nerve 9
The thoracic spinal nerve 9 is a spinal nerve of the thoracic segment..It originates from the spinal column from below the thoracic vertebra 9 ....

 (T9) passes out underneath it.

The xiphisternum (or xyphoid process of the sternum) is at the same level in the axial plane.

Tenth thoracic vertebra

The tenth thoracic vertebra has (except in the cases just mentioned) an entire articular facet (not demi-facet) on either side, which is placed partly on the lateral surface of the pedicle. It doesn't have any kind of facet below, because the following ribs only have one facet on their heads.

The thoracic spinal nerve 10
Thoracic spinal nerve 10
The thoracic spinal nerve 10 is a spinal nerve of the thoracic segment..It originates from the spinal column from below the thoracic vertebra 10 ....

 (T10) passes out underneath it.

Eleventh thoracic vertebra

In the eleventh thoracic vertebrae the body approaches in its form and size to that of the lumbar vertebrae.

The articular facets for the heads of the ribs are of large size, and placed chiefly on the pedicles, which are thicker and stronger in this and the next vertebrae than in any other part of the thoracic region.

The spinous process is short, and nearly horizontal in direction.

The transverse processes are very short, tuberculated at their extremities, and have no articular facets.

The thoracic spinal nerve 11
Thoracic spinal nerve 11
The thoracic spinal nerve 11 is a spinal nerve of the thoracic segment..It originates from the spinal column from below the thoracic vertebra 11 ....

 (T11) passes out underneath it.

Twelfth thoracic vertebra

The twelfth thoracic vertebra has the same general characteristics as the eleventh, but may be distinguished from it by its inferior articular surfaces being convex and directed lateralward, like those of the lumbar vertebrae; by the general form of the body, laminae, and spinous process, in which it resembles the lumbar vertebrae; and by each transverse process being subdivided into three elevations, the superior, inferior, and lateral tubercles: the superior and inferior correspond to the mammillary and accessory processes of the lumbar vertebrae. Traces of similar elevations are found on the transverse processes of the tenth and eleventh thoracic vertebrae.

The thoracic spinal nerve 12
Thoracic spinal nerve 12
The thoracic spinal nerve 12 is a spinal nerve of the thoracic segment..It originates from the spinal column from below the thoracic vertebra 12 ....

(T12) passes out underneath it.

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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