The
spinal column (or vertebral column) extends from the skull to
the pelvis and is made up of 33 individual bones termed vertebrae.
The vertebrae are stacked on top of each other group into four
regions:
Term
#
of Vertebrae
Body
Area
Abbreviation
Cervical
7
Neck
C1
– C7
Thoracic
12
Chest
T1
– T12
Lumbar
5
or 6
Low
Back
L1
– L5
Sacrum
5
(fused)
Pelvis
S1
– S5
Coccyx
3
Tailbone
None
The
cervical spine is further divided into two parts; the upper
cervical region (C1 and C2), and the lower cervical region (C3
through C7). C1 is termed the Atlas and C2 the Axis. The Occiput
(CO), also known as the Occipital Bone, is a flat bone that
forms the back of the head.
Atlas (C1)
The Atlas is the first cervical vertebra and therefore abbreviated
C1. This vertebra supports the skull. Its appearance is different
from the other spinal vertebrae. The atlas is a ring of bone
made up of two lateral masses joined at the front and back by
the anterior arch and the posterior arch.
The
Axis is the second cervical vertebra or C2. It is a blunt tooth–like
process that projects upward. It is also referred to as the
‘dens’ (Latin for ‘tooth’) or odontoid
process. The dens provides a type of pivot and collar allowing
the head and atlas to rotate around the dens.
Thoracic Vertebrae (T1 – T12)
The thoracic vertebrae increase in size from T1 through T12.
They are characterized by small pedicles, long spinous processes,
and relatively large intervertebral foramen (neural passageways),
which result in less incidence of nerve compression.
The
rib cage is joined to the thoracic vertebrae. At T11 and T12,
the ribs do not attach and are so are called "floating ribs."
The thoracic spine's range of motion is limited due to the
many rib/vertebrae connections and the long spinous processes.
Lumbar
Vertebrae (L1 – L5)
The lumbar vertebrae graduate in size from L1 through L5. These
vertebrae bear much of the body's weight and related biomechanical
stress. The pedicles are longer and wider than those in the
thoracic spine. The spinous processes are horizontal and more
squared in shape. The intervertebral foramen (neural passageways)
are relatively large but nerve root compression is more common
than in the thoracic spine.
Purpose
of the Vertebrae
Although vertebrae range in size; cervical the smallest, lumbar
the largest, vertebral bodies are the weight bearing structures
of the spinal column. Upper body weight is distributed through
the spine to the sacrum and pelvis. The natural curves in the
spine, kyphotic and lordotic, provide resistance and elasticity
in distributing body weight and axial loads sustained during
movement.
The vertebrae are composed of many elements that are critical
to the overall function of the spine, which include the intervertebral
discs and facet joints.
Functions
of the Vertebral or Spinal Column Include:
