Vertebra
Vertebrae (
singular: vertebra) are the individual irregular
bones that make up the
vertebral column (
aka spine) — a flexuous and flexible column.There are 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.
A typical vertebra consists of two essential parts: an
anterior (front) segment, which is the
vertebral body; and a posterior part – the
vertebral or
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.
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 or spinal column), 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 processess 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.
Note: For more detailed information, see Cervical vertebraeThese are generally small and delicate. Their spinous processes are short (with the exception of C7 which has the first palpable spinous process), and often split. Numbered top-to-bottom from C1-C7,
atlas (C1) and
axis (C2), are the vertebrae that allow the
neck so much rotation. Specifically, the atlas allows the
skull to move up and down, while the axis allows the upper neck to twist left and right. The axis also sits upon the first intervertebral disk of the spinal column.
Note: For more detailed information, see Thoracic vertebraeTheir 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.
Note: For more detailed information, see Lumbar vertebraeThese 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.
Note: For more detailed information, see Sacral vertebraeThere are 5 vertebrae (S1-S5). They are fused, with no
intervertebral discs.
Note: For more detailed information, see Coccygeal vertebraeThere are 3-5 vertebrae (Co1-Co5), again fused, with no
intervertebral discs.
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 will persist 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 fewer than normal cervical vertebrae, 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.
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Bone terminology*
Terms for anatomical location*
Clearing the cervical spine*
Gray's Anatomy:
The Vertebral column - The
1917 Gray's Anatomy is available via the
Bartleby project. It is available with full colour diagrams, and provides an excellent starting point in
anatomy, as well as a relatively complete source for
gross anatomy. This article was copied and pasted from the 1917 Gray's Anatomy, which is in the
public domain.
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Smart implant will help broken vertebra - An article from IsraCast
