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The vertebral column is a unique structure that extends from the base
of the skull to the pelvis. The column consists of 34 individual bones
called vertebrae (singular, vertebra).
The vertebral column also includes the spinal cord and nerves, tendons,
muscles, ligaments, intervertebral discs, and blood supply. This intricate
system works together to keep the body active.
Purpose and Function
The vertebral column protects the spinal cord and many internal organs,
serves as a base of attachment for tendons and ligaments, provides structural
support, connects the upper and lower body, and enables a wide range of
body movement. The bones in the vertebral column also store minerals and
produce red blood cells.
Regions of the Vertebral Column
The vertebral column is divided into regions: Cervical (neck), Thoracic
(chest), Lumbar (low back), Sacrum (pelvis) and Coccyx (tailbone). Most
people have 34 vertebrae, divided between the regions as shown in Table
1.
Table 1
| Region |
Body Area |
Number of Vertebrae |
| Cervical |
Neck |
7 (C1 through C7) |
| Thoracic |
Chest |
12 (T1 through T12) |
| Lumbar |
Low back |
5 (L1 through L5) |
| Sacrum |
Pelvis |
5 fused bones |
| Coccyx |
Tailbone |
5 fused bones |
Vertebrae
Although vertebrae at each level have physical differences, there are
common elements. The front (anterior) portion of the vertebra is called
the body. The body is round (when viewed from above), thick, dense and
contains most of the vertebra's mass. The outer layer of bone, called
cortical bone, is compact and surrounds the interior matrix of cancellous
or spongy bone. Within this area, new blood cells and other tissues are
formed.
The back (posterior) portion of the vertebra has several finger-like
projections called processes. The processes provide a place of attachment
for tendons and ligaments.
Linking the posterior and anterior portions of the vertebrae are pedicles.
These are short, round processes made of thick, strong bone.
Between the front and back portions of the vertebra is the spinal canal.
The spinal cord travels through the bony, tube-like spinal canal, thus
receiving some protection from external forces.
Intervertebral Discs
Separating the vertebrae from each other are the intervertebral
discs. These "cushions" absorb the stress and shock that the
body incurs during movement. They also enable multiplanar motion in the
spinal column.
Spinal Cord and Nerves
The spinal cord is part of the central nervous system. It is
located immediately below the brain stem, and extends to the L1 vertebra.
The cord relays information between the brain and the skin, muscles, ligaments,
organs and joints.
Muscles and Ligaments
Ligaments are bands of tough fibrous tissue that connect two
or more structures such as bones or cartilage. In the spine they are anchored
to the cortical bone of the vertebrae. Ligaments protect joints from becoming
hyper extended or hyper flexed.
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Muscles of the Posterior Cervical and Upper Thoracic Spine
1 Semispinalis Capitus (head rotation/pulls backward)
2 Iliocostalis Cervicis (extends cervical vertebrae)
3 Longissimus Cervicus (extends cervical vertebrae)
4 Longissimus Capitus (head rotation/pulls backward)
5 Longissimus Thoracis (extension/lateral flexion vertebral column, rib rotation)
6 Iliocostalis Thoracis (extension/lateral flexion vertebral column, rib rotation)
7 Semispinalis Thoracis (extends/rotates vertebral column) |
Muscles are attached to bones by tendons. Muscles in the spine enable
people to stand erect and to move.
Natural Curvature of the Vertebral Column
There are two types of natural curves: kyphotic and lordotic.
Kyphotic curves are anteriorly concave ('hump back") and lordotic
curves are anteriorly convex ("sway back). Viewing the vertebral
column from the side (lateral) the spine resembles the letter "s".
Table 2
| Spinal Region |
Type Curve |
Normal Curvature |
| Cervical |
Lordosis (Lordotic) |
20 to 40 degrees |
| Thoracic |
Kyphosis (Kyphotic) |
20 to 40 degrees |
| Lumbar |
Lordosis |
40 to 60 degrees |
| Sacrum |
Kyphosis |
Fused |
These natural spinal curves help the spinal column to absorb and distribute
stress incurred during movement. They also add to the body's flexibility
and balance.
Conclusion
The vertebral column consists of complex anatomic elements that enable
us to lead active lives. Patients with a good understanding of the spine's
anatomy and function are the most able to maintain a healthy back.
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