Cervical Vertebrae
In vertebrates, cervical vertebrae
(singular: vertebra) are those vertebrae immediately inferior to the skull. In
humans, cervical vertebrae are the smallest of the true vertebrae, and can be
readily distinguished from those of the thoracic or lumbar regions by the
presence of a foramen (hole) in each transverse process, through which passes the
vertebral artery.
Characteristics
of Cervical Vertebrae
- The body of these three vertebrae is small, and broader from side to side than from front to back.
ü The
anterior and posterior surfaces are flattened and of equal depth; the former is
placed on a lower level than the latter, and
ü its
inferior border is prolonged downward, so as to overlap the upper and forepart
of the vertebra below.
- The upper surface is concave transversely, and presents a projecting lip on either side. the lower surface is concave from front to back, convex from side to side, and presents laterally shallow concavities which receive the corresponding projecting lips of the underlying vertebra.
- The pedicles are directed laterally and backward, and are attached to the body midway between its upper and lower borders, so that the superior vertebral notch is as deep as the inferior, but it is, at the same time, narrower.
- The laminae are narrow, and thinner above than below; the vertebral foramen is large, and of a triangular form.
- The spinous process is short and bifid, the two divisions being often of unequal size.
- The superior and inferior articular processes of cervical vertebrae have fused on either or both sides to form articular pillars, columns of bone that project laterally from the junction of the pedicle and lamina.
- The articular facets are flat and of an oval form:
ü the
superior face backward, upward, and slightly medially.
ü the
inferior face forward, downward, and slightly laterally.
- The transverse processes are each pierced by the foramen transversarium, which, in the upper six vertebrae, gives passage to the vertebral artery and vein, as well as a plexus of sympathetic nerves.
- The anterior portion is the homologue of the rib in the thoracic region, and is therefore named the costal process or costal element. It arises from the side of the body, is directed laterally in front of the foramen, and ends in a tubercle, the anterior tubercle.
- The posterior part, the true transverse process, springs from the vertebral arch behind the foramen, and is directed forward and laterally; it ends in a flattened vertical tubercle, the posterior tubercle.
Thoracic
Vertebrae
In vertebrates, thoracic vertebrae
compose the middle segment of the vertebral column, between the cervical
vertebrae and the lumbar vertebrae.[1] In humans, 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. Humans have 12 thoracic vertebrae.
General
Characteristics
- The bodies 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 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 are broad, thick, and imbricated – that is to say, they overlap those of subjacent vertebrae like tiles on a roof and connect with the pedicles to surround and protect the spinal cord.
- The intervertebral foramen is small, and circular, with two at each intervertebral level, one for the right and one for the left exiting nerve roots.
- The vertebral foramen is the large opening posterior to the vertebral body also known as the "spinal canal". It contains and protects the spinal cord at the thoracic level.
- The spinous process is long, triangular on coronal section, directed obliquely downward, arising from the lamina and ending 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.
Function
Spinous and transverse processes
serve as points of attachment for muscles and ligament.
Lumbar
Vertebrae
In human anatomy, the lumbar
vertebrae are the five vertebrae and are located between the rib cage and the
pelvis. They are also the largest segments of the vertebral column. Within the
transverse process, there are no foramen transversarium and no facets on the
sides of the body. They are designated L1 to L5, starting from the top. The
vertebral body of each lumbar vertebrae is large, wider from side to side than
from front to back and a little thicker in front than back. It is concave
behind, flattened or slightly concave above and below and deeply constricted in
front and at the sides.
General Characteristics
- The pedicles are are very strong, directed backward from the upper part of the vertebral body. They increase in sagittal width from 9 mm to 18 mm at L5.The pedicle is sometimes used as a portal of entrance into the vertebral body for fixation.
- The laminae are short, broad and strong. They form the posterior portion of the vertebral arch. The lamina are taller than wide in the upper lumbar region and it is wider than tall in the lower lumbar vertebra. The lamina also connect the spinous process to the pedicles.
- The vertebral foramen within the arch is triangular, larger than in the thoracic vertebrae, but smaller than in the cervical vertebrae.
- Spinous process-posterior projection from the junction of two laminae. It is thick, broad and quadrilateral shaped serves as an attachment point for stabilizing back muscles.
- Transverse process-thin, long and later posterior near the junction of the pedicle, lamina and superior articular process. It also has the same function as the spinous process.
- Superior articular process-superior projection near the junction of the pedicle and transverse process.
Function
The lumbar vertebrae are very
important in supporting the upper body in an upright position. They have an
increased in body sized compared to the other vertebrae. They also contain a
small portion of the spinal cord and other nervous tissues, thus provide
protection of these.
Sacrum
Vertebrae
There are 5 sacral vertebral bones.
They are represented by the symbols S1 through S5. The sacral vertebrae are
situated in the spinal column just below the lumbar vertebrae and right above
the coccyx, which is the lowest segment of the vertebral column. The sacral
vertebrae are normally found fused together to form the sacrum.
The sacrum articulates (connects)
with the pelvic girdle. In humans it is usually composed of five vertebrae,
which fuse in early adulthood. The top of the first (uppermost) sacral vertebra
articulates with the last (lowest) lumbar vertebra. The transverse processes of
the first three sacral vertebrae are fused to form wide lateral wings, or alae,
and articulate with the centre-back portions of the blades of the ilia to
complete the pelvic girdle. The sacrum is held in place in this joint, which is
called the sacroiliac, by a complex mesh of ligaments. Between the fused
transverse processes of the lower sacral vertebrae, on each side, are a series
of four openings (sacral foramina); the sacral nerves and blood vessels pass
through these openings. A sacral canal running down through the centre of the
sacrum represents the end of the vertebral canal; the functional spinal cord
ends at about the level of the first sacral vertebra, but its continuation, the
flume terminal, can be traced through the sacrum to the first coccygeal
vertebra.
The pelvic girdle differs between
men and woman. In a man, the pelvis is more massive and the iliac crests are
closer together. In a woman, the pelvis is more delicate and the iliac crests
are farther apart. These differences reflect the woman's role in pregnancy and
delivery of children. When a child is born, it must pass through its mother's
pelvis. If the opening is too small, a caesarean section may be necessary.
Functions
The
pelvic girdle serves several important functions in the body. It supports the
weight of the body from the vertebral column. It also protects and supports the
lower organs, including the urinary bladder, the reproductive organs, and the
developing foetus in a pregnant woman.
Coccyx
Vertebrae
The coccyx, commonly referred to as
the tailbone, is the final segment of the vertebral column in tailless primate.
Comprising three to five separate or fused vertebrae ( the coccygeal vertebrae
) below the sacrum, it is attached to the sacrum and the coccyx.
Professor Peter Abrahams has state
in his book entitled How The Body Works (published by Popular UK Pte Ltd WSM
Pinaccle House 17 – 25 Hartfield Road Wimbledon, London) that the coccyx
attached to the base of the sacrum, is the remains of the tail seen in our
primate relatives. It consists of a small pyramid- shaped bone formed from four
fused vertebrae, and allows the attachment of ligaments and muscles, forming
the anal sphincter.
General
Characteristics
- Usually formed of four rudimentary vertebrae (sometimes three or five). It articulates superiorly with the sacrum.
- In each of the first three segment may be traced a rudimentary body and particular and transverse processes, the last piece is a mere nodule bone.
- The transverse processes are most prominent and noticeable on the first coccygeal segment. All the segment are destitute of pedicles, laminae and spinous processes.
- The first is the largest , it resembles the lowest sacral vertebra, and often exists as a separate piece, the last three diminish in size from above downward.
- Most anatomy books wrongly state that the coccyx is normally fused in adult. In fact it has been shown that the coccyx may consist of up to five separate bone segments, the most common configuration being two or three segments.
Function
In humans and other tailless
primates, the coccyx is the remnant of a vestigial tail, but still not entirely
useless, it is an important attachment for various muscles, tendons and
ligament – which makes it necessary for physicians and patients to pay special
attention to these attachments when considering surgical removal the coccyx.
Additionally it is also a part or the weight- bearing tripod structure which
act as a support for a sitting person. When a person sits leaning forward, the
Ishium tuberosities and inferior rami of the ischium take most of the weight,
but as the sitting persons leans backward, more weight is transferred to the
coccyx.
